## Core Model Seminar next Tuesday

Carnegie Mellon Logic Seminar

3/29/2023 8:46:32

TUESDAY, April 4, 2023

Core Model Seminar: 1:30 - 3 PM Eastern,

**Online**, Martin Zeman, University of California, Irvine

Join Zoom Meeting:

https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09Meeting ID: 977 4973 3438

Passcode: 457791

TITLE: Distributivity of iterated club shooting and fine structural

models, part 1

ABSTRACT: Iterative adding closed unbounded sets through stationary sets found quite a few applications in set theory. One natural way to do this is adding club sets using posets consisting of initial segments of the desired clubs. In such situations, one important property of such iterations is sufficient amount of distributivity. In fact, establishing distributivity is often the main part of arguments that involve iterated club shooting.

There are two possible situations where one iteratively adds clubs.

First, for a fixed cardinal $\kappa$, one iteratively adds club subsets

of $\kappa^+$. This kind of construction proved to have many applications. Second, one may start with a cardinal $\delta$ and

iteratively add club subsets of cardinals $\kappa^+$ where $\kappa$

ranges over some set above $\delta$. Surprisingly, this kind of construction has not been much studied. In this talk we will focus on this situation.

In order to add a club subset of some stationary set $S$ the set $S$

must be large in a certain sense; such sets are called fat. It is known

that, consistently, iteratively adding club subsets of fat stationary sets

of $\omega_n$ on a tail-end of $n\in\omega$ followed by forming an

inverse limit at the end may collapse $\aleph_n$ to $\omega$. A strong form of fatness is the property of being the complement of a

non-reflecting stationary set. One can prove, using a fairly standard

argument, that if the iteration described above uses complements of

non-reflecting stationary sets instead of just fat sets, then such an

iteration is $(\omega_{n+1},\infty)$-distributive where $\omega_n$ is

the first active step in the iteration. One can also prove in ZFC that

the analogous amount of distributivity holds of longer iterations,

where the first active step is at $\delta$ and inverse limits are used

at singular steps, as long as the singular steps are of cofinality

$<\delta$. Passing through singular steps of cofinality $\ge\delta$

seems to be difficult, and we only know how to do this over a fine

structural model where the non-reflecting stationary sets are carefully

chosen. Even in such a seemingly special case, the method does have applications.

This is a part of a joint work of Foreman-Magidor-Zeman on games with filters.

## Nankai Logic Colloquium

Nankai Logic Colloquium

3/27/2023 11:47:29

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Samuel Coskey from Boise State University. This talk is going to take place this Friday, Mar 31, from 16:00 to 17:00(UTC+8, Beijing time).

Title: Borel classification of conjugacy problems

Abstract: We aim to study the complexity of conjugacy problems for automorphisms of countable graphs G. Since conjugacy is an equivalence relation on Aut(G), we will study complexity using the invariant descriptive set theory, that is, the Borel reducibility hierarchy. After introducing this background setup, we will give a series of examples of locally finite graphs G whose conjugacy problems have a variety of different complexities. We will see conjugacy problems which are smooth (completely classifiable), complete for hyperfinite relations (E0), complete for essentially countable Borel equivalence relations (E_infinity), and intermediate between E0 and E_infinity.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title ： The 22nd Nankai Logic Colloquium --Samuel Coskey

Time ： 16:00pm, Mar. 31, 2023 (Beijing Time)

Zoom Number ： 830 5925 5547

Passcode ： 890764

Link ： https://us02web.zoom.us/j/83059255547?pwd=V29IcGo0bWdyeitRdHc5eUhBSnNrQT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## Cross-Alps Logic Seminar (speaker: Ludovic Patey)

Cross-Alps Logic Seminar

3/27/2023 6:55:25

On Friday 31.03.2023 at 16.00

**Ludovic Patey** (CNRS)

will give a talk on

*Canonical notions of forcing in Reverse Mathematics*

Please refer to the usual webpage

of our LogicGroup for more details and the abstract of the talk. The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

All the best,Vincenzo
## Logic Seminar Wednesday 29 March 2023 17:00 hrs at NUS by Xie Ruofei

NUS Logic Seminar

3/27/2023 4:33:42

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 29 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#05-11
Talk via Zoom:
https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
Meeting ID: 830 4925 8042
Passcode: 1729=x3+y3
Speaker: Xie Ruofei
Title: Majorising the Optimal C.E. Supermartingale
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
In the article "Highness Properties Close to PA-Completeness", Greenberg,
Miller and Nies left the following questions:
(1) Is there a finite collection of functionals {Gamma_i:i

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/26/2023 22:31:00

This Week in Logic at CUNY:

- - - - Monday, Mar 27, 2023 - - - -

Logic and Metaphysics WorkshopDate: Monday, March 27, 4.15-6.15pm (NY time), GC 9206NOTE: Meetings this semester are in person only (no zoom)For meeting information, please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/ Gregory Taylor (CUNY)

Title: First-order logics over fixed domain

Abstract: What we call first-order logic over fixed domain was initiated, in a certain guise, by Peirce around 1885 and championed, albeit in idiosyncratic form, by Zermelo in papers from the 1930s. We characterize such logics model- and proof-theoretically and argue that they constitute exploration of a clearly circumscribed conception of domain-dependent generality. Whereas a logic, or family of such, can be of interest for any of a variety of reasons, we suggest that one of those reasons might be that said logic fosters some clarification regarding just what qualifies as a logical concept, a logical operation, or a logical law.

- - - - Tuesday, Mar 28, 2023 - - - -

- - - - Wednesday, Mar 29, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: ** Jim Otto.**

Date and Time: ** Wednesday March 29, 2023, 7:00 - 8:30 PM. ZOOM TALK**

Title:** P Time, A Bounded Numeric Arrow Category, and Entailments.**

Abstract: We revisit the characterization of the P Time functions from our McGill thesis.

1. We build on work of L. Roman (89) on primitive recursion and of A. Cobham (65) and Bellantoni-Cook(92) on P Time.

2. We use base 2 numbers with the digits 1 & 2. Let N be the set of these numbers. We split the tapes of a multi-tape Turing machine each into 2 stacks of digits 1 & 2. These are (modulo allowing an odd numberof stacks) the multi-stack machines we use to study P Time.

3. Let Num be the category with objects the finite products of N and arrows the functions between these. From its arrow category Num^2 we abstract the doctrine (here a category of small categories with chosen structure) PTime of categories with with finite products, base 2 numbers, 2-comprehensions, flat recursion, & safe recursion. Since PTime is a locally finitely presentable category, it has an initial category I. Our characterization is that the bottom of the image of I in Num^2 consists of the P Time functions.

4. We can use I (thinking of its arrows as programs) to run multi-stack machines long enough to get P Time.This is the completeness of the characterization.

5. We cut down the numeric arrow category Num^2, using Bellantoni-Cook growth & time bounds on the functions, to get a bounded numeric arrow category B. B is in the doctrine PTime. This yields the soundness of the characterization.

6. For example, the doctrine of toposes with base 1 numbers, choice, & precisely 2 truth values (which captures much of ZC set theory) likely lacks an initial category, much as there is an initial ring, but no initial field.

7. On the other hand, the L. Roman doctrine PR of categories with finite products, base 1 numbers, & recursion (that is, product stable natural numbers objects) does have an initial category as it consists of the strong models of a finite set of entailments. And is thus locally finitely presentable. We sketch the signature graph for these entailments. And some of these entailments. Similarly (but with more complexity) there are entaiments for the doctrine PTime.

- - - - Thursday, Mar 30, 2023 - - - -

- - - - Friday, Mar 31, 2023 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 31, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Benjamin Goodman, CUNY

**Σn-correct forcing axioms**

The standard method of producing a model of a forcing axiom from a supercompact cardinal in fact gives a model of an even stronger principle: that for every small name a and every Σ2 formula arphi such that φ(a) is forceable by and preserved under further forcing in our forcing class, there is a filter F which meets a desired collection of dense sets and also interprets a such that φ(aF) already holds. I will show how to generalize this result to formulas of higher complexity by starting with slightly stronger large cardinal assumptions, then discuss the bounded versions of these enhanced forcing axioms, their relationships to other similar principles, and their consequences.

Logic Workshop

CUNY Graduate Center

Friday March 31, 2:00pm-3:30pm, Room 6417

**Corey Switzer**, University of Vienna

**Galois-Tukey reductions and canonical structure in the Cichoń diagram**

Cardinal invariants of the continuum are cardinal numbers which, roughly, measure how 'badly' CH fails in various mathematical contexts such as analysis and topology. For instance the cardinal add(N) is the least κ for which there are κ many Lebesgue measure zero sets of reals whose union is not measure zero. Classical facts imply ℵ1≤add(N)≤2ℵ0 but the precise value is undetermined in ZFC and depends heavily on the axioms of set theory. Other numbers follow a similar pattern of 'the least size of a set of reals (Borel sets, etc) lacking a classical smallness property'.

The Cichoń diagram displays cardinal invariants related to Lebesgue measure (the null ideal), Baire category (the meager ideal) as well as the bounding and dominating numbers which concern growth rates of functions. Many surprising ZFC-inequalities exist between these cardinals suggesting a rich world living on the reals in various models of set theory. At the combinatorial heart of every proof of a ZFC inequality derives from a Galois-Tukey reduction: the (ZFC-provable) existence of a pair of continuous maps with simple properties that make sense outside of the context of logic and indeed would be sensible to any analyst or topologist.

In this talk we will discuss some recent work in progress on the descriptive complexity of maps witnessing consistent but non-provable implications. We will show using largely computability theoretic methods that in Gödel's constructible universe there are low level projective reductions between any two cardinal invariants - thus CH holds in a very 'definable' way, while in Solovay's model of 'all sets of reals are Lebesgue measurable' (and therefore the axiom of choice fails) there are no non-ZFC provable implications thus these cardinals are all as different as possible.

Next Week in Logic at CUNY:

- - - - Monday, Apr 3, 2023 - - - -

Logic and Metaphysics WorkshopDate: Monday, April 3, 4.15-6.15pm (NY time), GC 9206NOTE: Meetings this semester are in person only (no zoom)For meeting information, please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/Thomas Ferguson (Czech Academy of Sciences).

Title: Care-theoretic semantics: Problems and non-deterministic solutions

Abstract: In this talk I will present the details of a project of *care-theoretic semantics* in which a linguistic feature of care–rather than truth–is understood as the fundamental semantic property. I will review the details, including how adopting a bounds consequence position in which bounds are determined by considerations of topic allows one to determine both a theory of inference and theory of meaning on the basis of care alone. I will consider two challenges to the project: that of the *reconciliation of topic-theoretic and truth-theoretic bounds* (in which we need to acknowledge cases in which a position crosses both types of bounds) and *sui generis monstrous content* (in which two anodyne sentences together yield a content-theoretic violation). I will show that in both cases intuitions suggest the use of Nmatrices in the style of Avron and consider the merits of their employment in the care-theoretic setting.

- - - - Tuesday, Apr 4, 2023 - - - -

- - - - Wednesday, Apr 5, 2023 - - - -

**** April 5-13, 2023 Spring Recess CUNY Graduate Center ****

- - - - Thursday, Apr 6, 2023 - - - -

- - - - Friday, Apr 7, 2023 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, April 7, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Miha Habič, Bard College at Simon's Rock

**** April 5-13, 2023 Spring Recess CUNY Graduate Center ****

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to Jonas.Reitz12@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email Jonas.Reitz12@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

3/24/2023 4:41:58

Dear all,
The seminar meets on Wednesday March 29th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Peter Vojtáš -- Considerations on Galois--Tukey motivated by
complexity theory and reverse mathematics
We will try to walk through the landscape motivated by following
publications
Peter Vojtas. Generalized Galois-Tukey connections between
explicit relations on classical objects of real analysis, IMCP 6 (1993)
619-643
Andreas Blass. Questions and Answers -- A Category Arising in
Linear Logic, Complexity Theory, and Set Theory, LMSLN 222 (1995) 61-81
Damir D. Dzhafarov , Carl Mummert. Reverse Mathematics - Problems,
Reductions, and Proofs, Springer 2022
to perceive different phenomena, hoping to formulate some new
observations and problems Considerations on Galois--Tukey motivated by
complexity theory and reverse mathematics.
Best,
David

## (KGRC) guests, video recordings and notes, and four talks

Kurt Godel Research Center

3/23/2023 12:54:24

The KGRC welcomes as guests:
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August 15.
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC from
March 27 to March 31.
José Nicolás Nájar Salinas (host: Miguel Moreno) visits the KGRC and gives
a talk on March 29, see below.
Sergei Starchenko (host: Matthias Aschenbrenner) visits the KGRC from
April 16 to April 30 and gives a talk, details to be announced at a later
time.
Zoltán Vidnyánszky (host: Vera Fischer) visits the KGRC on April 20 and
gives a talk, details to be announced at a later time.
Fabian Kaak (host: Vera Fischer) visits the KGRC from May 23 to May 26 and
gives a short talk, details to be announced at a later time.
Jaroslav Šupina (host: Vera Fischer) visits the KGRC from June 18 to June
24 and gives a talk, details to be announced at a later time.
Nadiya Kolos (host: Miguel Moreno) visits the KGRC from June 19 to June 23
and gives a talk, details to be announced at a later time.
* * *
video recordings and slides:
For a video recording of part 1 of Miguel Moreno's tutorial, please use
https://univienna.zoom.us/rec/share/0CoE9CuBiOXjuXf9dMiFnu63mp4xQCYvQSzjDNFeQT9edwtb9hVwDO6PvBXhSUaH.agwwTP4Mj8fEhKRn
and passcode W^9Ej.h3
For part 2, please use
https://univienna.zoom.us/rec/share/ltSirTm_O_ONGvGOu-9yJavOaG9QrihlrRtgWNixtSbZZtFTH4gaN7NliBodw44R.dEi0C8qkgxq__Sxp
and passcode d3P&V1g$
Notes for the series so can be found here (and will also be updated here after
part 3 will be delivered):
https://mathematik.univie.ac.at/fileadmin/user_upload/f_mathematik/Events_News/Vortraege_Events/2023-24/KGRC_Set_Theory_2023-03_Miguel_Moreno.pdf
For a video recording of Silvain Rideau-Kikuchi's talk, please use
https://univienna.zoom.us/rec/share/WZ_GtG4tfySmIRU_O2axDtut8U8bxqNznZvCwk0rFd1nODm43gNH_UNMZUYdmV3j.-1kMmpCZag-qvkL6
and passcode @d1yoKnn
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, March 28
"Generalised Descriptive Set Theory, part III"
Miguel Moreno (KGRC)
During this talk we will discuss where in the generalized
Borel-reducibility hierarchy are the isomorphism relation of first order
complete theories. These theories are divided into two kinds: classifiable
and non-classifiable. To study the classifiable theories case is needed
the use of Ehrenfeucht-Frass games. On the other hand the study of the
non-classifiable theories is done by using colored ordered trees. The goal
of the talk is to see the classifiable theories case and sketch the ideas
of non-classifiable theories.
Time and Place
Talk at 3:00pm in hybrid mode: on-site as well as via Zoom
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom: If you need the Zoom data and have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!
(Students at Uni Wien are required to attend in person.)
Please direct any other questions about this talk to vera.fischer@univie.ac.at.
* * *
Mathematical Colloquium
Institut für Mathematik
Wednesday, March 29
"Independence Phenomena in Mathematics: Current Obstacles and Scenarios
for Solutions"
Sandra Müller (TU Wien)
The standard axioms of set theory, the Zermelo-Fraenkel axioms (ZFC), do
not suffice to answer all questions in mathematics. While this follows
abstractly from Kurt Gödel's famous incompleteness theorems, we nowadays
know numerous concrete examples for such questions. A large number of
problems in set theory, for example, regularity properties such as
Lebesgue measurability and the Baire property are not decided - for even
rather simple (for example, projective) sets of reals - by ZFC. Even many
problems outside of set theory have been shown to be unsolvable, meaning
neither their truth nor their failure can be proven from ZFC. A major part
of set theory is devoted to attacking this problem by studying various
extensions of ZFC and their properties. I will outline some of these
extensions and explain current obstacles in understanding their impact on
the set theoretical universe together with recent progress on these
questions and future scenarios. This work is related to the overall goal
to identify the "right" axioms for mathematics.
Time and Place
Coffee at 2:45pm
Talk at 3:15pm
Vinum cum Pane following the talk
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
12th floor
Sky Lounge
Please direct any questions about this talk to anton.mellit@univie.ac.at
or jose.luis.romero@univie.ac.at.
* * *
Model Theory Research Seminar
Kurt Gödel Research Center
Wednesday, March 29
"Definability In Abstract Elementary Classes"
José Nicolás Nájar Salinas
(Fundación Universidad América, CO)
The development of definability in the context of Abstract Elementary
Classes has been boosted by the recent work of Shelah and Villaveces in
which they prove that for every AEC $\mathcal{K}$ in a vocabulary $\tau$,
there is a sentence
$\psi\in\mathbb{L}_{\beth_2(\kappa)^{+++},\kappa}(\tau)$ axiomatizing
where $\kappa$ is the Löwenheim-Skolem number of the class. Vasey enlarges
$\tau$ to $\Tilde{\tau}$ and proves that if the AEC is tame and
type-short, there is a bijection between the Galois Types of the AEC and
the quantifier free types in an infinitary logic
$\mathbb{L}_{\lambda,\lambda}(\Tilde{\tau})$ for some suitable $\lambda$,
the semantic-syntactic correspondence. We extend the ideas of Vasey to
make a partial semantic-syntactic correspondence-like results between
Galois types and some types of the logic
$\mathbb{L}_{\beth_2(\kappa)^{+++},\kappa}(\tau)$. Part of this is joint
work with Andrés Villaveces.
Time and Place
Talk at 3:00pm
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Please direct any questions about this talk to
matthias.aschenbrenner@univie.ac.at.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, March 30
"Constraint Satisfaction Problems: algebraic and model-theoretic
challenges to distinguish the easy from the hard"
Michael Pinsker (TU Wien)
I will give a gentle introduction to current algebraic and model-theoretic
methods in the computational complexity of Constraint Satisfaction
Problems (CSPs).
A CSP is a computational problem where we are given variables and
constraints about them; the question is whether the variables can be
assigned values such that all constraints are satisfied. Numerous natural
computational problems, such as satisfiability of a given system of
equations over a field, are CSPs; in fact, any computational problem is
Turing-equivalent to a CSP.
Any CSP can be modeled by a relational structure, and conversely every
relational structure naturally defines a CSP. In view of humanity's
continuing quest to distinguish easy from hard problems in general, and
the class P (polynomial-time solvable problems, e.g. satisfiability of
linear equations over a field) from the class NP (polynomial-time
verifiable problems, e.g. satisfiability of a propositional formula) in
particular, the question arises which mathematical properties of a
relational structure make the corresponding CSP easy and which make it
hard. It turns out that particular algebraic invariants of the structure
often determine the borderline between different complexity classes. Hence
algebraic methods, combined with concepts from model theory as well as
from Ramsey theory in the case of infinite structures, yield appropriate
tools to determine the computational complexity of CSPs.
Time and Place
Talk at 3:00pm in hybrid mode: on-site as well as via Zoom
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
2nd floor
room HS 11
Zoom: If you need the Zoom data and have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!
(Students at Uni Wien are required to attend in person.)
Please direct any questions about this talk to
matthias.aschenbrenner@univie.ac.at.

## Nankai Logic Colloquium

Nankai Logic Colloquium

3/20/2023 11:01:17

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the morning.

Our speaker this week will be Christian Rosendal from the University of Maryland. This talk is going to take place this Friday, Mar.24 , from 9am to 10am(UTC+8, Beijing time).

Title: Amenability, optimal transport and cohomology of Banach modules

Abstract: Using tools from the theory of optimal transport, four results concerning isometric actions of amenable topological groups with potentially unbounded orbits are established. Specifically, consider an amenable topological group $G$ with no non-trivial homomorphisms to $\mathbb R$.

If $d$ is a compatible left-invariant metric on $G$, $E\subseteq G$ is a finite subset and $\epsilon>0$, there is a finitely supported probability measure $\beta$ on $G$ so that

$$

\max_{g,h\in E}\, {\sf W}(\beta g, \beta h)<\eps,

$$

where ${\sf W}$ denotes the {\em Wasserstein} or {\em optimal transport} distance between probability measures on the metric space $(G,d)$. When $d$ is the word metric on a finitely generated group $G$, this strengthens a well known theorem of H. Rei\-ter \cite{reiter}. Furthermore, when $G$ is locally compact, $\beta$ may be replaced by an appropriate probability density $f\in L^1(G)$.

Also, when $G\curvearrowright X$ is a continuous isometric action on a metric space, the space of Lipschitz functions on the quotient $X/\!\!/G$ is isometrically isomorphic to a $1$-complemented subspace of the Lipschitz functions on $X$. And finally every continuous affine isometric action of $G$ on a Banach space has a canonical invariant linear subspace.

These results generalise previous theorems due to Schneider--Thom and C\'uth--Doucha.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title ： The 21st Nankai Logic Colloquium --Christian Rosendal

Time ： 9:00am, Mar. 24, 2023 (Beijing Time)

Zoom Number ： 849 1206 9207

Passcode ： 929100

Link ： https://zoom.us/j/84912069207?pwd=TTBWakY4OE9sdVNuN2dza3IvemY3Zz09 Christia

_____________________________________________________________________

Best wishes,

Ming Xiao

## Logic Seminar Wed 22 March 2023 17:00 hrs at NUS by Takayuki Kihara

NUS Logic Seminar

3/20/2023 4:04:33

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 22 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#05-11
Speaker: Kihara Takayuki
Title: Topos-theoretic aspect of the degrees of unsolvability
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
Abstract:
In this talk, we examine the topos-theoretic aspect of the degrees of
(computable) unsolvability. One of the main interpretations of
constructive mathematics is Kleene's realizability interpretation,
which, as is well known, can be relativized by an oracle. In this
sense, an oracle can be a factor that causes a change in a model of
constructive mathematics.
Let us review this observation from another point of view: there is a
topos, called the effective topos, based on Kleene's realizability
interpretation. And relativizing the realizability interpretation to
an oracle yields a subtopos of the effective topos. Thus, the
structure of oracles, i.e., the structure of the degrees of
unsolvability, is expected to be closely related to the structure of
the subtoposes of the effective topos.
In this talk, we give a complete correspondence, in a strict sense,
between the structure of the degrees of unsolvability and the
structure of subtoposes of the effective topos (or its relatives).

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/19/2023 22:42:00

This Week in Logic at CUNY:

- - - - Monday, Mar 20, 2023 - - - -Rutgers Logic Seminar

Monday, March 20, 2pm, Rutgers University, Hill 005

Roman Kossak, CUNY

Absolute Undefinability

Logic and Metaphysics WorkshopDate: Monday, March 20th, 4.15-6.15 (NY time), GC Room 9205NOTE: Meetings this semester are in person only (no zoom)For meeting information, please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/ Speaker: Shawn Simpson (Pitt)

Title: Logic and inference in the sender-receiver model

Abstract: The sender-receiver model was developed by David Lewis to tackle the question of the conventionality of meaning. But many people who cared about the conventionality of meaning did so because they thought it was intimately connected to the conventionality of logic. Since Lewis’s work, only a few attempts have been made to say anything about the nature of logic and inference from the perspective of the sender-receiver model. This talk will look at the what’s been said in that regard, by Skyrms and others, and suggest a few general lessons.

- - - - Tuesday, Mar 21, 2023 - - - -Models of Peano Arithmetic (MOPA)Tuesday, March 21, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id) Bartosz Wcisło, University of Gdańsk

**Satisfaction classes with the full collection scheme**

Satisfaction classes are subsets of models of Peano arithmetic which satisfy Tarski's compositional clauses. Alternatively, we can view satisfaction or truth classes as the extension of a fresh predicate T(x) (the theory in which compositional clauses are viewed as axioms is called CT^-).

It is easy to see that CT^- extended with a full induction scheme is not conservative over PA, since it can prove, for instance, the uniform reflection over arithmetic. By a nontrivial argument of Kotlarski, Krajewski, and Lachlan, the sole compositional axioms of CT^- in fact form a conservative extension of PA. Moreover, in order to obtain non-conservativity it is enough to add induction axioms for the Delta_0 formulae containing the truth predicate.

Answering a question of Kaye, we will show that the theory of compositional truth, CT^- with the full collection scheme is a conservative extension of Peano Arithmetic. Following the initial suggestion of Kaye, we will in fact show that any countable recursively saturated model M of PA has an elementary omega_1-like end extension M' such that M' carries a full satisfaction class.

- - - - Wednesday, Mar 22, 2023 - - - -- - - - Thursday, Mar 23, 2023 - - - -- - - - Friday, Mar 24, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Friday March 24, 2:00pm-3:30pm, Room 6417

Victoria Gitman CUNY

**Parameter-free comprehension in second-order arithmetic**

Second-order arithmetic has two types of objects: numbers and sets of numbers, which we think of as the reals. The second-order arithmetic framework has been used successfully to investigate what kinds of real numbers need to exist to prove various significant results in analysis. One of the strongest second-order arithmetic axiomatizations is the theory Z2 consisting of the axioms PA (for numbers), the set induction axiom, and comprehension for all second-order formulas with set parameters. How significant is the inclusion of set parameters in the comprehension scheme? Let Z−p2 be like Z2, but where set parameters are not allowed in the comprehension scheme. Harvey Friedman showed that Z2 and Z−p2 are equiconsistent because parameter-free comprehension suffices to build a model's version of the constructible universe L inside the model and the 'constructible' reals satisfy Z2. Kanovei recently showed that models of Z−p2 can be very badly behaved, for example, their sets may not even be closed under complement. Kanovei also showed that there can be nicely behaved models of Z−p2 in which Σ12-comprehension (with set parameters) holds. He constructed his model in a forcing extension by a tree iteration of Sacks forcing. In Kanovei's model, Σ14-comprehension (with set parameters) fails and he asked whether this can be improved to Σ13-comprehension. In this talk, I will show how to construct a model of Σ12-comprehension and Z−p2 in which Σ13-comprehension fails. The model will be constructed in a forcing extension by a tree iteration of Jensen's forcing. Jensen's forcing is a sub-poset of Sacks forcing constructed by Jensen to show that it is consistent to have a non-constructible Π12-definable singleton real (every Σ12-definable set of reals is constructible by Shoenfield's Absoluteness).

Next Week in Logic at CUNY:

- - - - Monday, Mar 27, 2023 - - - -

Logic and Metaphysics WorkshopDate: Monday, March 27, 4.15-6.15pm (NY time), GC 9206NOTE: Meetings this semester are in person only (no zoom)For meeting information, please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/ Gregory Taylor (CUNY)

Title: First-order logics over fixed domain

Abstract: What we call first-order logic over fixed domain was initiated, in a certain guise, by Peirce around 1885 and championed, albeit in idiosyncratic form, by Zermelo in papers from the 1930s. We characterize such logics model- and proof-theoretically and argue that they constitute exploration of a clearly circumscribed conception of domain-dependent generality. Whereas a logic, or family of such, can be of interest for any of a variety of reasons, we suggest that one of those reasons might be that said logic fosters some clarification regarding just what qualifies as a logical concept, a logical operation, or a logical law.

- - - - Tuesday, Mar 28, 2023 - - - -

- - - - Wednesday, Mar 29, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: ** Jim Otto.**

Date and Time: ** Wednesday March 29, 2023, 7:00 - 8:30 PM. ZOOM TALK**

Title:** P Time, A Bounded Numeric Arrow Category, and Entailments.**

Abstract: We revisit the characterization of the P Time functions from our McGill thesis.

1. We build on work of L. Roman (89) on primitive recursion and of A. Cobham (65) and Bellantoni-Cook(92) on P Time.

2. We use base 2 numbers with the digits 1 & 2. Let N be the set of these numbers. We split the tapes of a multi-tape Turing machine each into 2 stacks of digits 1 & 2. These are (modulo allowing an odd numberof stacks) the multi-stack machines we use to study P Time.

3. Let Num be the category with objects the finite products of N and arrows the functions between these. From its arrow category Num^2 we abstract the doctrine (here a category of small categories with chosen structure) PTime of categories with with finite products, base 2 numbers, 2-comprehensions, flat recursion, & safe recursion. Since PTime is a locally finitely presentable category, it has an initial category I. Our characterization is that the bottom of the image of I in Num^2 consists of the P Time functions.

4. We can use I (thinking of its arrows as programs) to run multi-stack machines long enough to get P Time.This is the completeness of the characterization.

5. We cut down the numeric arrow category Num^2, using Bellantoni-Cook growth & time bounds on the functions, to get a bounded numeric arrow category B. B is in the doctrine PTime. This yields the soundness of the characterization.

6. For example, the doctrine of toposes with base 1 numbers, choice, & precisely 2 truth values (which captures much of ZC set theory) likely lacks an initial category, much as there is an initial ring, but no initial field.

7. On the other hand, the L. Roman doctrine PR of categories with finite products, base 1 numbers, & recursion (that is, product stable natural numbers objects) does have an initial category as it consists of the strong models of a finite set of entailments. And is thus locally finitely presentable. We sketch the signature graph for these entailments. And some of these entailments. Similarly (but with more complexity) there are entaiments for the doctrine PTime.

- - - - Thursday, Mar 30, 2023 - - - -

- - - - Friday, Mar 31, 2023 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 31, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Benjamin Goodman, CUNY

**Σn-correct forcing axioms**

The standard method of producing a model of a forcing axiom from a supercompact cardinal in fact gives a model of an even stronger principle: that for every small name a and every Σ2 formula arphi such that φ(a) is forceable by and preserved under further forcing in our forcing class, there is a filter F which meets a desired collection of dense sets and also interprets a such that φ(aF) already holds. I will show how to generalize this result to formulas of higher complexity by starting with slightly stronger large cardinal assumptions, then discuss the bounded versions of these enhanced forcing axioms, their relationships to other similar principles, and their consequences.

Logic Workshop

CUNY Graduate Center

Friday March 31, 2:00pm-3:30pm, Room 6417

Corey Switzer, University of Vienna

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org. v
## Wednesday seminar

Prague Set Theory Seminar

3/19/2023 16:28:14

Dear all,
The seminar meets on Wednesday March 22nd at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: David Uhrik -- Hajnal--Máté Graphs and Cohen Reals
We will study Hajnal--Máté (HM) graphs. The first construction of an HM
graph was from the diamond+ principle. Since then several other
constructions were provided with additional interesting properties, e.g.
having no triangles. We will survey results about this class of graphs
and provide a construction of a triangle free HM graph in a model after
adding a single Cohen real. Time permitting we will introduce a
generalization, so-called 𝛿-Hajnal--Máté graphs, and prove some of
their basic properties and deduce a weak partition relation on ω_2.
Best,
David

## (KGRC) Set Theory Seminar talk and Geometry and Analysis on Groups Seminar talk

Kurt Godel Research Center

3/16/2023 11:53:04

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August
15.
Lou van den Dries (host: Matthias Aschenbrenner) visits the KGRC from
March 10 to March 22.
Chieu-Minh Tran (host: Matthias Aschenbrenner) visits the KGRC from March
19 to March 22 and gives a talk on March 21, see below.
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC from
March 27 to March 31.
José Nicolás Nájar Salinas (host: Miguel Moreno) visits the KGRC and gives
a talk on March 29, details to be announced at a later time.
Sergei Starchenko (host: Matthias Aschenbrenner) visits the KGRC from
April 16 to April 30 and gives a talk, details to be announced at a later
time.
Zoltán Vidnyánszky (host: Vera Fischer) visits the KGRC on April 20 and
gives a talk, details to be announced at a later time.
Jaroslav Šupina (host: Vera Fischer) visits the KGRC from June 18 to June
24 and gives a talk, details to be announced at a later time.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, March 21
"Generalised Descriptive Set Theory, part II"
Miguel Moreno (KGRC)
We have introduced the notions of K-Borel class, K-analytic class,
K-analytic-coanalytic class, K-Borel* class in the previous talk. In
descriptive set theory the Borel class, the analytic-coanalytic class, and
the Borel* class are the same class, we showed that this doesn't hold in
the generalized descriptive set theory.
In this talk, we will show the consistency of "K-Borel* class is equal to
the K-analytic class". This was initially proved by Hyttinen and Weinstein
(former Kulikov), under the assumption V=L. We will show a different proof
that shows that this holds in L but also can be forced by a
cofinality-preserving GCH-preserving forcing from a model of GCH, but also
by a 3.99 \mu(A)$. We also show a more general result for the
product of two sets, which can be seen as a Brunn-Minkowski-type
inequality for sets with small measure in $\mathrm{SO}(3,\mathbb{R})$.
(Joint with Yifan Jing and Ruixiang Zhang)
Time and Place
Talk at 3:00pm
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
9th floor
room BZ 9
Please direct any questions about this talk to
matthias.aschenbrenner@univie.ac.at.

## Logic Seminar today in person in S17#05-11

NUS Logic Seminar

3/15/2023 4:58:53

Hello, here just a reminder for the
talk of Liu Shixiao in the logic seminar
today at 17:00 hrs (now) on Forcing with
Density Requirements. The abstract is:
In the first half of the talk I shall be proving the
Properness of Mathias forcing with lower density
requirements. In the second half of the talk
I shall demonstrate the difficulty in applying
this method (and some other commonly used methods)
to Silver forcing with lower density requirement.
The location is S17#05-11 in the Department of
Mathematics, NUS.
Best regards, Frank

## Nankai Logic Colloquium

Nankai Logic Colloquium

3/14/2023 8:02:25

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the morning.

Our speaker this week will be Konstantin Slutsky from Iowa State University. This talk is going to take place this Friday, Mar. 17, from 9am to 10am(UTC+8, Beijing time).

**Title:** Partial actions and orbit equivalence relations

**Abstract:** In this talk, we will discuss the framework of partial actions for constructing orbit equivalent actions of Polish groups. While related ideas have been employed in ergodic theory and Borel dynamics for many years, the particular viewpoint of partial actions simplifies construction of orbit equivalent actions of distinct groups.

As an application, we will present a Borel version of Katok's representation theorem for multidimensional Borel flows. One-dimensional flows are closely connected to actions of $\mathbb{Z}$ via the so-called "flow under a function" construction. This appealing geometric picture does not generalize to higher dimensions. Within the ergodic theoretical framework, Katok introduced the concept of a special flow as a way to connect multidimensional $\mathbb{R}^d$ and $\mathh{Z}^d$ actions. We will show that similar connections continue to hold in Borel dynamics.

Another illustration of the partial actions techniques that we intend to touch is the following result: a Borel equivalence relation generated by a free $\mathbb{R}$-flow can also be generated by a free action of any non-discrete and non-compact Polish group. This is in contrast with the situation for discrete groups, where amenability distinguishes groups that can and cannot generate free finite measure-preserving hyperfinite actions.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 20th Nankai Logic Colloquium --Konstantin Slutsky

Time： 9:00am, Mar. 17, 2023 (Beijing Time)

Zoom Number：811 5076 2263

Passcode： 201148

Link： https://zoom.us/j/81150762263?pwd=UmdvRkVEUjI2MHlONHQrdmQrRFJyZz09

_____________________________________________________________________

Best wishes,

Ming Xiao

## Cross-Alps Logic Seminar (speaker: Victor Selivanov)

Cross-Alps Logic Seminar

3/13/2023 8:20:27

On Friday 17.03.2023 at 16.00

**Victor Selivanov** (Institute of Informatics Systems, Novosibirsk)

will give a talk on

*Boole vs Wadge: Comparing Basic Tools of Descriptive Set Theory*

Please refer to the usual webpage

of our LogicGroup for more details and the abstract of the talk. The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

All the best,Vincenzo
## CosmoCaixa Barcelona: Joel Hamkins: pensament estratègic en jocs infinits

Barcelona Logic Seminar

3/13/2023 6:26:31

Dear All,

Just a reminder that you may get a 3 Euros admission fee for the Cosmocaixa museum, on the occasion of Joel hamkins’ talk. Go to the link below to get the entrance ticket and use the following code:

I strongly encourage you to attend Joel’s talk, and visit the Cosmocaixa!

See you there!

Joan

Benvolguts,

us envio l’anunci de la conferència que farà Joel Hamkins al Cosmocaixa el dia 16 de març a les 7. L’entrada val 6 Euros, però us puc donar un codi que la redueix a 3. Inclou la visita al Cosmocaixa.

Joel Hamkins: pensament estratègic en jocs infinits

https://cosmocaixa.org/ca/p/pensament-estrategic-en-jocs-infinits_a122155152 .

Espero que vingueu,

Joan

Dear All,

here is the announcement of the talk by Joel Hamkins he will give at Cosmocaixa (Science Museum in Barcelona) on March 16, 7pm. The entry fee is 6 Euros, but I can give you a code that reduces it to 3 Euros. It includes the entrance to the museum

Joel Hamkins: Strategic Thinking in Infinite Games

https://cosmocaixa.org/ca/p/pensament-estrategic-en-jocs-infinits_a122155152 .

Hope to see you there!

Joan

neal

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

## Wednesday seminar

Prague Set Theory Seminar

3/13/2023 5:16:47

Dear all,
The seminar meets on Wednesday March 15th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
There is no fixed program yet. Participants are encouraged to bring
their topics and questions to share.
(Chris is leaving for couple of months at the end of the week, so this
will be for some time the last opportunity to ask him something. ;-)
Best,
David

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/12/2023 22:44:00

This Week in Logic at CUNY:

- - - - Monday, Mar 13, 2023 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 13, 4.15-6.15pm (NY time), GC 9206

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Melvin Fitting (CUNY)

Title: On Kripke’s proof of Kripke completeness

Abstract: Saul Kripke announced his possible world semantics in 1959, and `published his proof of axiomatic completeness for the standard modal logics of the time in 1963. It is very unlike the standard completeness proof used today, which involves a Lindenbaum/Henkin construction and produces canonical models. Kripke’s proof involved tableaus, in a format that is difficult to follow, and uses tableau construction algorithms that are complex and somewhat error prone to describe. I will first discuss Kripke’s proof, then the historical origins of the modern version. Then I will show that completeness, proved Kripke style, could actually have been done in the Lindenbaum/Henkin way, thus simplifying things considerably. None of this is new but, with the parts collected together it is an interesting story. “In my end is my beginning”.

- - - - Tuesday, Mar 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, March 14, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Bartosz Wcisło, University of Gdańsk

**Satisfaction classes with the full collection scheme**

Satisfaction classes are subsets of models of Peano arithmetic which satisfy Tarski's compositional clauses. Alternatively, we can view satisfaction or truth classes as the extension of a fresh predicate T(x) (the theory in which compositional clauses are viewed as axioms is called CT^-).

It is easy to see that CT^- extended with a full induction scheme is not conservative over PA, since it can prove, for instance, the uniform reflection over arithmetic. By a nontrivial argument of Kotlarski, Krajewski, and Lachlan, the sole compositional axioms of CT^- in fact form a conservative extension of PA. Moreover, in order to obtain non-conservativity it is enough to add induction axioms for the Delta_0 formulae containing the truth predicate.

Answering a question of Kaye, we will show that the theory of compositional truth, CT^- with the full collection scheme is a conservative extension of Peano Arithmetic. Following the initial suggestion of Kaye, we will in fact show that any countable recursively saturated model M of PA has an elementary omega_1-like end extension M' such that M' carries a full satisfaction class.

- - - - Wednesday, Mar 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: Jens Hemelaer, University of Antwerp.

Date and Time: Wednesday March 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.

Title: EILC toposes.

Abstract: In topos theory, local connectedness of a geometric morphism is a very geometric property, in the sense that it is stable under base change, can be checked locally, and so on. In some situations however, the weaker property of being essential is easier to verify. In this talk, we will discuss EILC toposes: toposes E such that any essential geometric morphism with codomain E is automatically locally connected. It turns out that many toposes of interest are EILC, including toposes of sheaves on Hausdorff spaces and classifying toposes of compact groups.

- - - - Thursday, Mar 16, 2023 - - - -

- - - - Friday, Mar 17, 2023 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 17, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Jonathan Osinski, University of Hamburg

**Model-Theoretic Characterizations of Weak Vopěnka's Principle**

It has been known since the 1980s that Vopěnka's Principle (VP) is equivalent to certain statements about logics, e.g. to the schema 'Every logic has a compactness cardinal.' On the other hand, it was only recently shown by Trevor Wilson that a related statement statement called Weak Vopěnka's Principle (WVP) is strictly weaker than VP. In fact, Joan Bagaria and Wilson showed that WVP is equivalent to the existence of Πn-strong cardinals for all natural numbers n. We generalize logical characterizations of strong cardinals to achieve a characterization of Πn-strong cardinals and therefore of WVP in terms of properties of strong logics. This is partly joint work with Will Boney and partly with Trevor Wilson.

Logic Workshop

CUNY Graduate Center

Friday March 17, 2:00pm-3:30pm, Room 6417

**Filippo Calderoni**, Rutgers University

**Rotation equivalence and rigidity**

The theory of countable Borel equivalence relations analyzes the actions of countable groups on Polish spaces. The main question studied is how much information is encoded by the corresponding orbit space. The amount of encoded information reflects the extent to which the action is rigid.

In this talk we will discuss rigidity results for the action of the group of rational rotations. In particular we will analyze the rotation equivalence on spheres in higher dimension. This is connected to superrigidity results of Margulis and to Zimmer’s program about the actions of discrete subgroups of Lie groups on manifolds.

Next Week in Logic at CUNY:- - - - Monday, Mar 20, 2023 - - - -Rutgers Logic Seminar

Monday, March 20, 2pm, Rutgers University, Hill 005

Roman Kossak, CUNY

Absolute Undefinability

Logic and Metaphysics WorkshopDate: Monday, March 20, 4.15-6.15pm (NY time), GC 9206NOTE: Meetings this semester are in person only (no zoom)For meeting information, please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/ Gregory Taylor (CUNY)

Title: First-order logics over fixed domain

Abstract: What we call first-order logic over fixed domain was initiated, in a certain guise, by Peirce around 1885 and championed, albeit in idiosyncratic form, by Zermelo in papers from the 1930s. We characterize such logics model- and proof-theoretically and argue that they constitute exploration of a clearly circumscribed conception of domain-dependent generality. Whereas a logic, or family of such, can be of interest for any of a variety of reasons, we suggest that one of those reasons might be that said logic fosters some clarification regarding just what qualifies as a logical concept, a logical operation, or a logical law.

- - - - Tuesday, Mar 21, 2023 - - - -- - - - Wednesday, Mar 22, 2023 - - - -- - - - Thursday, Mar 23, 2023 - - - -- - - - Friday, Mar 24, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Friday March 24, 2:00pm-3:30pm, Room 6417

Victoria Gitman CUNY

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## (KGRC) talks on Tuesday, March 14 and Thursday, March 16

Kurt Godel Research Center

3/10/2023 10:44:02

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August
15.
Lou van den Dries (host: Matthias Aschenbrenner) visits the KGRC from
March 10 to March 22.
Silvain Rideau-Kikuchi (host: Matthias Aschenbrenner) visits the KGRC from
March 15 to March 20 and gives a talk, see below.
José Nicolás Nájar Salinas (host: Miguel Moreno) visits the KGRC and gives
a talk on March 29, details to be announced at a later time.
Sergei Starchenko (host: Matthias Aschenbrenner) visits the KGRC from
April 16 to April 30 and gives a talk, details to be announced at a later
time.
* * *
For a video recording of Juris Steprāns's talk, please use
https://univienna.zoom.us/rec/share/_U6vJ6rbIaT1WaoflIav52OiR4GsAQ-W3Aw00aD4jb08xvlf7C4QoQJyD_KlQkEc.h7MOui67bVxLr9Cl
and passcode jTi%8uqf
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, March 14
"Generalised Descriptive Set Theory, part I"
Miguel Moreno (KGRC)
This is the first of three talks about Generalised Descriptive Set Theory.
The aim of this talk is to introduce the notions of K‑Borel class,
K‑analytic class, K‑analytic-coanalytic class, K‑Borel* class, and show
the relation between these classes.
Time and Place
Talk at 3:00pm in hybrid mode: on-site as well as via Zoom
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom: If you need the Zoom data and have not received the meeting link by
the day before the talk, please contact richard.springer@univie.ac.at!
(Students at Uni Wien are required to attend in person.)
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, March 16
"Multi topological fields, approximations and NTP2"
Silvain Rideau-Kikuchi (U Paris Diderot, FR)
(Joint work with S. Montenegro)
The striking resemblance between the behaviour of pseudo-algebraically
closed, pseudo real closed and pseudo p-adically fields has lead to
numerous attempts at describing their properties in a unified manner. In
this talk I will present another of these attempts: the class of
pseudo-T-closed fields, where T is an enriched theory of fields. These
fields verify a « local-global » principle with respect to models of T for
the existence of points on varieties. Although it very much resembles
previous such attempts, our approach is more model theoretic in flavour,
both in its presentation and in the results we aim for.
The first result I would like to present is an approximation result,
generalising a result of Kollar on PAC fields, respectively Johnson on
henselian fields. This result can be rephrased as the fact that
existential closeness in certain topological enrichments come for free
from existential closeness as a field. The second result is a (model
theoretic) classification result for bounded pseudo-T-closed fields, in
the guise of the computation of their burden. One of the striking
consequence of these two results is that a bounded perfect PAC field with
n independent valuations has burden n and, in particular, is NTP2.
Time and Place
Talk at 3:00pm in hybrid mode: on-site as well as via Zoom
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
2nd floor
room HS 11
Zoom: If you need the Zoom data and have not received the meeting link by
the day before the talk, please contact richard.springer@univie.ac.at!
(Students at Uni Wien are required to attend in person.)
Please direct any other questions about this talk to
matthias.aschenbrenner@univie.ac.at.

## Nankai Logic Colloquium

Nankai Logic Colloquium

3/6/2023 22:47:15

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Vladimir Kanovei from the Institute for Information Transmission Problems, RAS. This talk is going to take place this Friday, Mar.10, from 4pm to 5pm(UTC+8, Beijing time).

Title:

On the significance of parameters in the choice and сomprehension schemata in the 2nd-order Peano arithmetic
Abstract
Parameters are free variables in various axiom schemata in PA, ZFC, and other similar theories.
Given an axiom schema S, we let S* be the parameter-free sub-schema.
Kreisel (A survey of proof theory, JSL 1968) was one of those who paid attention to the comparison of some schemata in second-order PA and their parameter-free versions.
In particular, Kreisel noted that
[...] if one is convinced of the significance of something like agiven axiom schema, it is natural to study details, such as the effect of parameters.
This talk is devoted to the effect of parameters in the schemata of Comprehension and Choice in second-order arithmetic.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 19th Nankai Logic Colloquium --Vladimir Kanovei

Time： 16:00pm, Mar. 10, 2023 (Beijing Time)

Zoom Number：844 4116 3813

Passcode： 628524

Link： https://zoom.us/j/84441163813?pwd=WFlSbThMbldUeVZYZncrTGVyYmp5QT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## UPDATE - This Week in Logic at CUNY

This Week in Logic at CUNY

3/6/2023 10:34:51

Hi everyone,

A quick update - Unfortunately, Dr. Weinert will be unable to speak on March 10, so the Logic Workshop is canceled this week.

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Mar 6, 2023 - - - -

Rutgers Logic Seminar

Monday, March 6, 2pm, Rutgers University, Hill 005

Will Adkisson, UIC

The Strong and Super Tree Property

Logic and Metaphysics Workshop

Date: Monday, March 6, 4.15-6.15pm (NY time), GC 9206

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Gary Ostertag (CUNY/Mount Sinai)

Title: Lewis on accommodation and representation de re

Abstract: Recall Lumpl, the lump of clay out of which the statue Goliath is fashioned. While (1) ‘Lumpl could have survived a squashing’ is true, (2) ‘Goliath could have survived a squashing’ is false, it being after all essential to Goliath, but not to Lumpl, that it be a statue. We have here an example of what David Lewis (1986) called “the inconstancy of representation de re”. For Lewis, the inconstancy does not amount to inconsistency, but rather points to the context-sensitivity of de re modal predication: (1) and (2) make implicit, context-sensitive reference to different counterpart relations. Once we recognize this, Lewisians argue, it becomes clear how our intuitive truth-conditional judgments are fully consistent. As I show, however, the conversational rule that triggers the implicit reference not only fails to license the reference shift, it effectively prohibits it. The upshot is that counterpart theory is deprived of a central motivation.

- - - - Tuesday, Mar 7, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, March 7, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Bellaouar Djamel, University 08 Mai 1945 Guelma

**Some generalizations on the representation of unlimited natural numbers**

Based on permanence principles of nonstandard analysis and as a continuation of the papers [1-3], we present some notes and questions on the representation of unlimited natural numbers. As a natural generalization, let A be an unlimited m by n matrix with integer entries (i.e one of its integer entries is unlimited). Here we prove that every unlimited matrix A with integer entries can be written as the sum of a limited matrix S with integer entries and the product of two unlimited matrices W1 and W2 with integer entries, that is, A=S+W1⋅W2. For further research, we propose several matrix representation forms.

Finally, we consider the numbers of the form z=a+bi where a,b are integers, which are called Gaussian integers. In the case when a or b is unlimited, the number z=a+bi is said to be unlimited. Also, some notes on the representation of unlimited Gaussian integers are given.

[1] A. Boudaoud, La conjecture de Dickson et classes particulière d'entiers, Ann. Math. Blaise Pascal. 13 (2006), 103-109.

[2] A. Boudaoud and D. Bellaouar, Representation of integers: A nonclassical point of view, J. Log. Anal. 12:4 (2020) 1-31.

[3] K. Hrbacek, On Factoring of unlimited integers, J. Log. Anal. 12:5 (2020) 1-6.

- - - - Wednesday, Mar 8, 2023 - - - -

- - - - Thursday, Mar 9, 2023 - - - -

- - - - Friday, Mar 10, 2023 - - - -

Logic Workshop - TODAY'S WORKSHOP IS CANCELLED

CUNY Graduate Center

Friday March 10, 2:00pm-3:30pm, Room 6417

Set Theory Seminar

CUNY Graduate Center

Friday, March 10, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. James Holland, Rutgers University

Next Week in Logic at CUNY:

- - - - Monday, Mar 13, 2023 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 13, 4.15-6.15pm (NY time), GC 9206

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Melvin Fitting (CUNY)

Title: On Kripke’s proof of Kripke completeness

Abstract: Saul Kripke announced his possible world semantics in 1959, and `published his proof of axiomatic completeness for the standard modal logics of the time in 1963. It is very unlike the standard completeness proof used today, which involves a Lindenbaum/Henkin construction and produces canonical models. Kripke’s proof involved tableaus, in a format that is difficult to follow, and uses tableau construction algorithms that are complex and somewhat error prone to describe. I will first discuss Kripke’s proof, then the historical origins of the modern version. Then I will show that completeness, proved Kripke style, could actually have been done in the Lindenbaum/Henkin way, thus simplifying things considerably. None of this is new but, with the parts collected together it is an interesting story. “In my end is my beginning”.

- - - - Tuesday, Mar 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, March 14, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Bartosz Wcisło, University of Gdańsk

- - - - Wednesday, Mar 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: Jens Hemelaer, University of Antwerp.

Date and Time: Wednesday March 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.

Title: EILC toposes.

Abstract: In topos theory, local connectedness of a geometric morphism is a very geometric property, in the sense that it is stable under base change, can be checked locally, and so on. In some situations however, the weaker property of being essential is easier to verify. In this talk, we will discuss EILC toposes: toposes E such that any essential geometric morphism with codomain E is automatically locally connected. It turns out that many toposes of interest are EILC, including toposes of sheaves on Hausdorff spaces and classifying toposes of compact groups.

- - - - Thursday, Mar 16, 2023 - - - -

- - - - Friday, Mar 17, 2023 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 17, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Jonathan Osinski, University of Hamburg

Logic Workshop

CUNY Graduate Center

Modality TBA

Friday March 17, 2:00pm-3:30pm, Room 6417

Filippo Calderoni, Rutgers University

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## This Week in Logic at CUNY

This Week in Logic at CUNY

3/5/2023 22:46:00

This Week in Logic at CUNY:

- - - - Monday, Mar 6, 2023 - - - -

Rutgers Logic Seminar

Monday, March 6, 2pm, Rutgers University, Hill 005

Will Adkisson, UIC

The Strong and Super Tree Property

Logic and Metaphysics Workshop

Date: Monday, March 6, 4.15-6.15pm (NY time), GC 9206

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Gary Ostertag (CUNY/Mount Sinai)

Title: Lewis on accommodation and representation de re

Abstract: Recall Lumpl, the lump of clay out of which the statue Goliath is fashioned. While (1) ‘Lumpl could have survived a squashing’ is true, (2) ‘Goliath could have survived a squashing’ is false, it being after all essential to Goliath, but not to Lumpl, that it be a statue. We have here an example of what David Lewis (1986) called “the inconstancy of representation de re”. For Lewis, the inconstancy does not amount to inconsistency, but rather points to the context-sensitivity of de re modal predication: (1) and (2) make implicit, context-sensitive reference to different counterpart relations. Once we recognize this, Lewisians argue, it becomes clear how our intuitive truth-conditional judgments are fully consistent. As I show, however, the conversational rule that triggers the implicit reference not only fails to license the reference shift, it effectively prohibits it. The upshot is that counterpart theory is deprived of a central motivation.

- - - - Tuesday, Mar 7, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, March 7, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Bellaouar Djamel, University 08 Mai 1945 Guelma

**Some generalizations on the representation of unlimited natural numbers**

Based on permanence principles of nonstandard analysis and as a continuation of the papers [1-3], we present some notes and questions on the representation of unlimited natural numbers. As a natural generalization, let A be an unlimited m by n matrix with integer entries (i.e one of its integer entries is unlimited). Here we prove that every unlimited matrix A with integer entries can be written as the sum of a limited matrix S with integer entries and the product of two unlimited matrices W1 and W2 with integer entries, that is, A=S+W1⋅W2. For further research, we propose several matrix representation forms.

Finally, we consider the numbers of the form z=a+bi where a,b are integers, which are called Gaussian integers. In the case when a or b is unlimited, the number z=a+bi is said to be unlimited. Also, some notes on the representation of unlimited Gaussian integers are given.

[1] A. Boudaoud, La conjecture de Dickson et classes particulière d'entiers, Ann. Math. Blaise Pascal. 13 (2006), 103-109.

[2] A. Boudaoud and D. Bellaouar, Representation of integers: A nonclassical point of view, J. Log. Anal. 12:4 (2020) 1-31.

[3] K. Hrbacek, On Factoring of unlimited integers, J. Log. Anal. 12:5 (2020) 1-6.

- - - - Wednesday, Mar 8, 2023 - - - -

- - - - Thursday, Mar 9, 2023 - - - -

- - - - Friday, Mar 10, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Modality TBA

Friday March 10, 2:00pm-3:30pm, Room 6417

Thilo Weinert, University of Vienna

Set Theory Seminar

CUNY Graduate Center

Friday, March 10, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. James Holland, Rutgers University

Next Week in Logic at CUNY:

- - - - Monday, Mar 13, 2023 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 13, 4.15-6.15pm (NY time), GC 9206

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Melvin Fitting (CUNY)

Title: On Kripke’s proof of Kripke completeness

Abstract: Saul Kripke announced his possible world semantics in 1959, and `published his proof of axiomatic completeness for the standard modal logics of the time in 1963. It is very unlike the standard completeness proof used today, which involves a Lindenbaum/Henkin construction and produces canonical models. Kripke’s proof involved tableaus, in a format that is difficult to follow, and uses tableau construction algorithms that are complex and somewhat error prone to describe. I will first discuss Kripke’s proof, then the historical origins of the modern version. Then I will show that completeness, proved Kripke style, could actually have been done in the Lindenbaum/Henkin way, thus simplifying things considerably. None of this is new but, with the parts collected together it is an interesting story. “In my end is my beginning”.

- - - - Tuesday, Mar 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, March 14, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Bartosz Wcisło, University of Gdańsk

- - - - Wednesday, Mar 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: Jens Hemelaer, University of Antwerp.

Date and Time: Wednesday March 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.

Title: EILC toposes.

Abstract: In topos theory, local connectedness of a geometric morphism is a very geometric property, in the sense that it is stable under base change, can be checked locally, and so on. In some situations however, the weaker property of being essential is easier to verify. In this talk, we will discuss EILC toposes: toposes E such that any essential geometric morphism with codomain E is automatically locally connected. It turns out that many toposes of interest are EILC, including toposes of sheaves on Hausdorff spaces and classifying toposes of compact groups.

- - - - Thursday, Mar 16, 2023 - - - -

- - - - Friday, Mar 17, 2023 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 17, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Jonathan Osinski, University of Hamburg

Logic Workshop

CUNY Graduate Center

Modality TBA

Friday March 17, 2:00pm-3:30pm, Room 6417

Filippo Calderoni, Rutgers University

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Barcelona Set Theory Seminar

Barcelona Logic Seminar

3/4/2023 11:13:28

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: Radek Honzik

TITLE: Compactness principles at small cardinals and their preservation

DATE: Wednesday, 8 March 2023

TIME: 16:00 (CET)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

## Wednesday seminar

Prague Set Theory Seminar

3/3/2023 9:24:32

Dear all,
The seminar meets on Wednesday March 8th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Chris Lambie-Hanson -- Topics in cardinal arithmetic
We will discuss some recent results and some not-so-recent results in
cardinal arithmetic and PCF theory. The precise topics will depend on
the interests of the audience and the preparedness of the speaker but
may include: existence theorems about PCF-theoretic scales, Silver's
theorem for pseudopowers, the cov vs. pp problem, or recent work of the
speaker showing that a generalized narrow system property implies
Shelah's Strong Hypothesis.
Best,
David

## (KGRC) two talks at U Wien and TU Wien

Kurt Godel Research Center

3/2/2023 10:31:00

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August
15.
Juris Steprāns (host: Vera Fischer) visits the KGRC from March 6 to March
10 and gives a talk, see below.
Lou van den Dries (host: Matthias Aschenbrenner) visits the KGRC from
March 10 to March 22.
Silvain Rideau-Kikuchi (host: Matthias Aschenbrenner) visits the KGRC from
March 15 to March 20 and gives a talk, details to be announced at a later
time.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, March 7
"Selective and Milliken-Taylor ultrafilters"
Juris Steprāns (York U, CA)
I will report on joint work with Dilip Raghavan solving a question of
Blass about whether the existence of many selective ultrafilters implies
the existence of Milliken-Taylor ultrafilters. The first part of the talk
will provide the historical context of what was known in the mid 80s that
prompted Blass to ask his question. The second part will discuss the key
technical advance in our argument.
Time and Place
Talk at 3:00pm
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * *
FG1 Seminar
Algebra Research Unit
Wednesday, March 8
"Various ways to compare spaces, subsets, and functions"
Raphaël Carroy (Università degli Studi di Torino, IT)
One can consider a quasi-order like topological embeddability when one
wants to compare a Polish (or analytic) space to another. If instead one
tries to rank the complexities emerging among subsets of a given space,
continuous reducibility becomes relevant. Both these quasi-orders have
extensions to functions between Polish (or analytic) spaces. Some natural
questions about these quasi-orders are then: the existence of simple
bases, characterizing the simplicity or complexity of the quasi-order in
itself, and describing it when it turns out to be simple enough.
I will try to give some context on these quasi-orders and review known and
more recent results and applications.
Times and Places
Snacks and beverages at 2:00pm
Institute of Discrete Mathematics and Geometry
TU Wien
Wiedner Hauptstrasse 8-10
1040 Wien
Austria
5th floor, green part
room Besprechungsraum DA 05 C22
Talk at 2:45pm
Institute of Discrete Mathematics and Geometry
TU Wien
Wiedner Hauptstrasse 8-10
1040 Wien
Austria
8th floor, green part
room Dissertantenraum DA 08 B19
Please direct any questions about this talk to
sandra.mueller@tuwien.ac.at.

## CosmoCaixa Barcelona: Joel Hamkins: pensament estratègic en jocs infinits

Barcelona Logic Seminar

3/2/2023 9:02:35

Benvolguts,

us envio l’anunci de la conferència que farà Joel Hamkins al Cosmocaixa el dia 16 de març a les 7. L’entrada val 6 Euros, però us puc donar un codi que la redueix a 3. Inclou la visita al Cosmocaixa.

Joel Hamkins: pensament estratègic en jocs infinits

https://cosmocaixa.org/ca/p/pensament-estrategic-en-jocs-infinits_a122155152 .

Espero que vingueu,

Joan

Dear All,

here is the announcement of the talk by Joel Hamkins he will give at Cosmocaixa (Science Museum in Barcelona) on March 16, 7pm. The entry fee is 6 Euros, but I can give you a code that reduces it to 3 Euros. It includes the entrance to the museum

Joel Hamkins: Strategic Thinking in Infinite Games

https://cosmocaixa.org/ca/p/pensament-estrategic-en-jocs-infinits_a122155152 .

Hope to see you there!

Joan

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

## Logic Seminar 8 March 2023 17:00 hrs at NUS by Chong Chitat

NUS Logic Seminar

3/2/2023 3:58:53

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 8 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#05-11
Speaker: Chong Chitat, National University of Singapore
Title: Proof-theoreitic strength of the Halpern-Lauchli Theorem
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
Abstract:
Let T be the full infinite binary tree (i.e. the Cantor space). An
infinite subtree S of T is a strong subtree if (i) S is isomorphic to
T, (ii) if sigma is a node in S, and sigma_0, sigma_1 are its
immediate successors in S, then sigma_0 and sigma_1 have the same
length in T and furthermore (iii) the intersection of sigma_0 and
sigma_1 is sigma.
The Halpern-Lauchli Theorem is a theorem in combinatorial mathematics
which states that for any finite number of infinite full binary trees
T_1,T_2,..., T_d, and any finite coloring of the d-row vectors in T_1 x
T_2 x ... x T_d, there exist strong subtrees S_1 subseteq T_1, S_2 subseteq
T_2, ..., S_d subseteq T_d for which all d-row vectors in
S_1 x S_2 x ... x S_d have the same color.
This Ramsey type theorem is yet another striking demonstration of the
existence of order within chaotic disorder. There is no known simple
proof of this theorem in the published literature.
In this talk we discuss the proof-theoretic strength of the
Halpern-Lauchli theorem from the reverse mathematics point of view. In
particular, we give a characterisation of the inductive strength of
this theorem as well as its conservation strength over a base theory
weaker than Sigma_2-induction.
This is joint work with Li Wei and Yang Yue.

## Today's Logic Seminar is via Zoom

NUS Logic Seminar

3/1/2023 3:29:00

Hello, please note that today's talk is by Zoom and there
is no physical meeting. Here again the login info:
Return-Path:
Date: Fri, 24 Feb 2023 15:00:41 +0800
From: Frank STEPHAN
To: matyangy@nus.edu.sg, settheorytalks@gmail.com, belanger@nus.edu.sg,
Subject: Logic Seminar 1 March 2023 17:00 hrs Singapore time by Linus Richter
Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 1 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, Talk via Zoom:
https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
Meeting ID: 830 4925 8042
Passcode: 1729=x3+y3
Speaker: Linus Richter, Victoria University of Wellington
Title: Co-analytic Counterexamples to Marstrand's Projection Theorem
Abstract: A recent "point-to-set principle" of Jack Lutz and Neil Lutz
characterises the Hausdorff dimension of any subset of Euclidean space
in terms of the Kolmogorov complexity of its individual points.
Sets with particular fractal properties can now be constructed
point-by-point, by coding "enough" information into each point, bit-by-bit.
After introducing the point-to-set principle, I will present a new result
in fractal geometry: under V=L (the axiom of constructiblity),
I will outline the construction of co-analytic sets of Euclidean
space which fail Marstrand's Projection Theorem, a classical result
in fractal geometry concerning the dimension of orthogonal projections
of analytic plane sets onto lines.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Nankai Logic Colloquium

Nankai Logic Colloquium

2/27/2023 22:39:50

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Martino Lupini from the University of Bologna. This talk is going to take place this Friday, Mar. 03, from 16:00 to 17:00 (UTC+8, Beijing time).

Title: Definable refinements of classical algebraic invariants

Abstract: In this talk I will explain how methods from logic allow one to construct refinements of classical algebraic invariants that are endowed with additional topological and descriptive set-theoretic information. This approach brings to fruition initial insights due to Eilenberg, Mac Lane, and Moore (among others) with the additional ingredient of recent advanced tools from logic. I will then present applications of this viewpoint to invariants from a number of areas in mathematics, including operator algebras, group theory, algebraic topology, and homological algebra.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 18th Nankai Logic Colloquium --Martino Lupini

Time： 16:00, Mar. 3, 2023 (Beijing Time)

Zoom Number：859 1679 0296

Passcode： 577088

Link： https://zoom.us/j/85916790296?pwd=WGRrZjJKa0kvRE9KSGtxNkJia2JiUT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## Cross-Alps Logic Seminar (speaker: Dugald MacPherson)

Cross-Alps Logic Seminar

2/27/2023 11:53:59

On Friday 03.03.2023 at 16.00

**Dugald MacPherson** (University of Leeds)

will give a talk on

*Uniform families of definable sets in finite structures*

Please refer to the usual webpage

of our LogicGroup for more details and the abstract of the talk. The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

All the best,Vincenzo
## (KGRC) Logic Colloquium talk on Thursday, March 2

Kurt Godel Research Center

2/27/2023 10:24:16

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August
15.
Jerzy Kąkol (host: Damian Sobota) visits the KGRC until March 3.
Manuel López Pellicer (host: Damian Sobota) visits the KGRC until March 3.
Katrin Tent (host: Matthias Aschenbrenner) visits the KGRC from March 1 to
March 5 and gives a talk (see below).
Juris Steprāns (host: Vera Fischer) visits the KGRC from March 6 to March
10 and gives a talk, details to be announced at a later time.
Silvain Rideau-Kikuchi (host: Matthias Aschenbrenner) visits the KGRC from
March 15 to March 20 and gives a talk, details to be announced at a later
time.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, March 2
"Simplicity of automorphism groups of homogeneous structures"
Katrin Tent (Universität Münster, DE)
We discuss some general criteria that can be used to show that the
automorphism group of a homogeneous structure (such as metric space,
right-angled building, graph or hypergraphs) are simple groups or have
simple quotients.
Time and Place
Talk at 3:00pm
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
2nd floor room HS 11
If you would like to follow the talk online, please let Matthias
Aschenbrenner (matthias.aschenbrenner@univie.ac.at) or Vera Fischer
(vera.fischer@univie.ac.at) know in advance and we will arrange for it to
be streamed.

## Wednesday seminar

Prague Set Theory Seminar

2/27/2023 6:31:41

Dear all,
The seminar meets on Wednesday March 1st at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
The program is not yet determined. If anybody is interested in speaking
or to hear something specific, do let me know.
Best,
David

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/26/2023 22:34:00

This Week in Logic at CUNY:

- - - - Monday, Feb 27, 2023 - - - -

Rutgers Logic Seminar

Monday, February 27, 2pm, Rutgers University, Hill 005

Leonardo Nagami Coregliano, IAS Princeton

Ramsey's Theorem in the countable and weak randomness

Logic and Metaphysics Workshop

Date: Monday, February 27, 4.15-6.15pm (NY time), GC 9205

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Lionel Shapiro, UConn

Title: Neopragmatism and logic: A deflationary proposal

Abstract: Neopragmatists seek to sidestep metaphysical puzzles by shifting the target of philosophical explanation from the objects we think and talk about to the functions of expressions and concepts in our cognitive economy. Logical vocabulary can serve as a target for neopragmatist inquiry, and it has also posed obstacles to neopragmatist accounts of other vocabulary. I will argue that the obstacles can be addressed by adopting a neopragmatist perspective toward logical relations, such as logical consequence, and toward propositional content. Doing so calls into question two purported constraints on explanations of the functions of logical connectives. I will sketch an account made possible by rejecting those constraints, one according to which logical connectives serve to express dialectical attitudes. The proposal is deflationary in two ways: it rests on an extension of deflationism from truth to logical relations, and it aims to deflate some of neopragmatists’ theoretical ambitions.

- - - - Tuesday, Feb 28, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 28, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)**Zuzana Hanikova**, Czech Academy of Sciences

**Vopěnka's Alternative Set Theory and its mathematical context**

Vopěnka first presented his Alternative Set Theory (AST) in the monograph 'Mathematics in the Alternative Set Theory' published by Teubner, Leipzig in 1979. Another book presenting the theory, 'Introduction to Mathematics in the Alternative Set Theory', was published in 1989 in Slovak by Alfa, Bratislava. In addition there are numerous journal papers on the AST by members of the research group established by Vopěnka, and the proceedings of a conference dedicated to the AST, also from 1989. In several essays, Vopěnka sought to lay out the motivation and philosophical import of the AST and some of his subsequent work. As one consequence of the emphasis on his philosophy, the mathematical inspiration for the AST has been somewhat obliterated. The aim of the talk is to discuss the design choices Vopěnka made for the AST in relation to pertinent mathematical developments of the 20th century, such as Skolem's work on nonstandard models of arithmetic, Robinson's nonstandard analysis, Rieger's nonstandard models of arithmetic, Vopěnka's nonstandard model of set theory, Vopěnka and Hájek's theory of semisets, or Parikh's almost consistent theories. The presentation will include an outline of the AST following the works of Vopěnka and Sochor. This is a historical talk; no new mathematical results on the AST will be presented.

- - - - Wednesday, Mar 1, 2023 - - - -

- - - - Thursday, Mar 2, 2023 - - - -

- - - - Friday, Mar 3, 2023 - - - -

Next Week in Logic at CUNY:

- - - - Monday, Mar 6, 2023 - - - -

Rutgers Logic Seminar

Monday, March 6, 2pm, Rutgers University, Hill 005

Will Adkisson, UIC

Logic and Metaphysics Workshop

Date: Monday, March 6, 4.15-6.15pm (NY time), GC 9205

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Gary Ostertag (CUNY/Mount Sinai)

Title: Lewis on accommodation and representation de re

Abstract: Recall Lumpl, the lump of clay out of which the statue Goliath is fashioned. While (1) ‘Lumpl could have survived a squashing’ is true, (2) ‘Goliath could have survived a squashing’ is false, it being after all essential to Goliath, but not to Lumpl, that it be a statue. We have here an example of what David Lewis (1986) called “the inconstancy of representation de re”. For Lewis, the inconstancy does not amount to inconsistency, but rather points to the context-sensitivity of de re modal predication: (1) and (2) make implicit, context-sensitive reference to different counterpart relations. Once we recognize this, Lewisians argue, it becomes clear how our intuitive truth-conditional judgments are fully consistent. As I show, however, the conversational rule that triggers the implicit reference not only fails to license the reference shift, it effectively prohibits it. The upshot is that counterpart theory is deprived of a central motivation.

- - - - Tuesday, Mar 7, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, March 7, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Bellaouar Djamel, University 08 Mai 1945 Guelma

**Some generalizations on the representation of unlimited natural numbers**

Based on permanence principles of nonstandard analysis and as a continuation of the papers [1-3], we present some notes and questions on the representation of unlimited natural numbers. As a natural generalization, let A be an unlimited m by n matrix with integer entries (i.e one of its integer entries is unlimited). Here we prove that every unlimited matrix A with integer entries can be written as the sum of a limited matrix S with integer entries and the product of two unlimited matrices W1 and W2 with integer entries, that is, A=S+W1⋅W2. For further research, we propose several matrix representation forms.

Finally, we consider the numbers of the form z=a+bi where a,b are integers, which are called Gaussian integers. In the case when a or b is unlimited, the number z=a+bi is said to be unlimited. Also, some notes on the representation of unlimited Gaussian integers are given.

[1] A. Boudaoud, La conjecture de Dickson et classes particulière d'entiers, Ann. Math. Blaise Pascal. 13 (2006), 103-109.

[2] A. Boudaoud and D. Bellaouar, Representation of integers: A nonclassical point of view, J. Log. Anal. 12:4 (2020) 1-31.

[3] K. Hrbacek, On Factoring of unlimited integers, J. Log. Anal. 12:5 (2020) 1-6.

- - - - Wednesday, Mar 8, 2023 - - - -

- - - - Thursday, Mar 9, 2023 - - - -

- - - - Friday, Mar 10, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Modality TBA

Friday March 10, 2:00pm-3:30pm, Room 6417

Thilo Weinert, University of Vienna

Set Theory Seminar

CUNY Graduate Center

Friday, March 10, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. James Holland, Rutgers University

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Barcelona Set Theory Seminar

Barcelona Logic Seminar

2/25/2023 2:50:59

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: Boriša Kuzeljević

TITLE: Lower bounds of sets of P-points

DATE: Wednesday, 29 February 2023

TIME: 16:00 (CET)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

## BLAST in Charlottle NC: May 16-20, 2023

Conference

2/24/2023 13:53:57

We would like to bring your attention to the upcoming BLAST 2023 conference, which will take place at the University of North Carolina, Charlotte, from May 16 - 20.
BLAST is a conference series focusing on Boolean Algebras, Lattices, Universal Algebra and Model Theory, Set Theory, and Topology. We hope that you will be able to attend the conference, and to contribute a talk.
The confirmed invited speakers for the conference are:
- Marco Abbadini, University of Salerno
- Dana Bartošová, University of Florida
- William Chan, University of North Texas
- Daniel Herden, Baylor University
- Andre Kornell, Dalhousie University
- David Stanovský, Charles University
Additionally, we can confirm that a tutorial will be given by
- Keith Kearnes, University of Colorado Boulder
The website for this conference is still under construction, but a preliminary version can be found here: https://pages.charlotte.edu/blast2023/. The home website for the BLAST conference series can be found here: https://math.colorado.edu/blast/.
Some financial support, provided by the National Science Foundation, is available for students and young researchers.

Tagged: Marco Abbadini, Dana Bartošová, William Chan, Daniel Herden, Andre Kornell, David Stanovský, Keith Kearnes

## CMU Math Logic Seminar next Tuesday

Carnegie Mellon Logic Seminar

2/24/2023 10:53:57

TUESDAY, February 28, 2023

Mathematical Logic Seminar: 3:30-4:30 PM Eastern,

**Online**, Marcin Sabok, McGill University

Join Zoom Meeting:

https://cmu.zoom.us/j/92655324096?pwd=VUhSSlkrdHMxbTlSYUMxYzFXM01kdz09Meeting ID: 926 5532 4096

Passcode: 555455

TITLE: Perfect matchings in hyperfinite graphings

ABSTRACT: The talk will focus on recent results on measurable perfect matchings in hyperfinite graphings. In particular, we will discuss a result saying that every regular hyperfinite one-ended bipartite graphing admits a measurable perfect matching. We will also see some applications of these results, answering several questions in the field. For instance we will characterize the existence of factor of iid perfect matchings in bipartite Cayley graphs, extending a result of Lyons and Nazarov. We will also answer a question of Bencs, Hruskova and Toth arising in the study of balanced orientations in graphings. Finally, we see how the results imply the measurable circle squaring. This is joint work with Matt Bowen and Gabor Kun.

## Logic Seminar 1 March 2023 17:00 hrs Singapore time by Linus Richter at NUS via Zoom

NUS Logic Seminar

2/24/2023 2:00:41

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 1 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, Talk via Zoom:
https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
Meeting ID: 830 4925 8042
Passcode: 1729=x3+y3
Speaker: Linus Richter, Victoria University of Wellington
Title: Co-analytic Counterexamples to Marstrand's Projection Theorem
Abstract: A recent "point-to-set principle" of Jack Lutz and Neil Lutz
characterises the Hausdorff dimension of any subset of Euclidean space
in terms of the Kolmogorov complexity of its individual points.
Sets with particular fractal properties can now be constructed
point-by-point, by coding "enough" information into each point, bit-by-bit.
After introducing the point-to-set principle, I will present a new result
in fractal geometry: under V=L (the axiom of constructiblity),
I will outline the construction of co-analytic sets of Euclidean
space which fail Marstrand's Projection Theorem, a classical result
in fractal geometry concerning the dimension of orthogonal projections
of analytic plane sets onto lines.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Nankai Logic Colloquium

Nankai Logic Colloquium

2/22/2023 20:20:08

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the morning.

Our speaker this week will be Slawomir Solecki from Cornell University. This talk is going to take place this Friday, Feb.24, 2023, from 9am to 10am (UTC+8, Beijing time).

Title: Descriptive Set Theory and closed groups generated by generic measure preserving transformations

Abstract: The subject matter of the talk lies within the area that employs the descriptive set theoretic point of view in the study of large topological groups.

The behavior of a measure preserving transformation, even a generic one, is highly non-uniform. In contrast to this observation, a different picture of a very uniform behavior of the closed group generated by a generic measure preserving transformation $T$ has emerged. This picture included substantial evidence that pointed to these groups (for a generic $T$) being all topologically isomorphic to a single group, namely, $L^0$---the topological group of all Lebesgue measurable functions from $[0,1]$ to the circle. In fact, Glasner and Weiss asked if this is the case.

We will describe the background touched on above, including the descriptive set theoretic background. We will indicate a proof of the following theorem that answers the Glasner--Weiss question in the negative: for a generic measure preserving transformation $T$, the closed group generated by $T$ is {\bf not} topologically isomorphic to $L^0$.

____________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 17th Nankai Logic Colloquium --Slawomir Solecki

Time： 9:00am, Feb. 24, 2023 (Beijing Time)

Zoom Number：854 3647 9165

Passcode： 977845

Link： https://zoom.us/j/85436479165?pwd=cjFwZlpUZWtCcnhTci9OK0R5ODU0UT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/19/2023 22:31:00

This Week in Logic at CUNY:

- - - - Monday, Feb 13, 2023 - - - -

Rutgers Logic Seminar

Monday, February 13, 2pm, Rutgers University, Hill 005

James Holland, Rutgers

Forcing more choice over the Chang model

- - - - Tuesday, Feb 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 14, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id) Vladimir Kanovei, Institute for Information Transmission Problems

**On the significance of parameters in the choice and сomprehension schemata in the 2nd-order Peano arithmetic**

Parameters are free variables in various axiom schemata in PA, ZFC, and other similar theories. Given an axiom schema S, we let S* be the parameter-free sub-schema.

Kreisel (A survey of proof theory, JSL 1968) was one of those who paid attention to the comparison of some schemata in second-order PA and their parameter-free versions. In particular, Kreisel noted that

[...] if one is convinced of the significance of something like a given axiom schema, it is natural to study details, such as the effect of parameters.This talk is devoted to the effect of parameters in the schemata of Comprehension and Choice in second-order arithmetic.

- - - - Wednesday, Feb 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, Second Lecture.

Speaker: ** Mee Seong Im, United States Naval Academy, Annapolis.**

Date and Time: ** Wednesday February 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Automata and topological theories.**

Abstract: Theory of regular languages and finite state automata is part of the foundations of computer science. Topological quantum field theories (TQFT) are a key structure in modern mathematical physics. We will interpret a nondeterministic automaton as a Boolean-valued one-dimensional TQFT with defects labelled by letters of the alphabet for the automaton. We will also describe how a pair of a regular language and a circular regular language gives rise to a lax one-dimensional TQFT.

- - - - Thursday, Feb 16, 2023 - - - -

- - - - Friday, Feb 17, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Friday February 17, 2:00pm-3:30pm, Room 6417

**Russell Miller**, CUNY

**Computability and the Absolute Galois Group of Q**

Fix a computable presentation ¯¯¯¯Q of the algebraic closure of the rational numbers. The absolute Galois group of the rational numbers, which is precisely the automorphism group of the field ¯¯¯¯Q, may then be viewed as a collection of paths through a finite-branching tree. Each individual automorphism has a Turing degree. We will use known results in computability to try to build natural countable elementary subgroups of the absolute Galois group. Several intriguing questions in number theory will appear as we measure the extent to which we succeed in doing so.

Next Week in Logic at CUNY:

- - - - Monday, Feb 20, 2023 - - - -

- - - - Tuesday, Feb 21, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 21, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Alexei Miasnikov, Stevens Institute of Technology

**First-order classification and non-standard models**

In this talk I will discuss some recent advances in the first-order classification problem. I will touch on first-order rigidity and quasi finite axiomatization. However, the main point of the presentation is on how, in principle, one can describe all structures which are first-order equivalent to a given one. This leads to non-standard models of algebraic structures (aka non-standard analysis or non-standard arithmetic), which are interesting in their own right.

- - - - Wednesday, Feb 22, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, **Third Lecture.**

Speaker: Joshua Sussan, **CUNY.**

Date and Time: ** Wednesday February 22, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Non-semisimple Hermitian TQFTs.**

Abstract: Topological quantum field theories coming from semisimple categories build upon interesting structures in representation theory and have important applications in low dimensional topology and physics. The construction of non-semisimple TQFTs is more recent and they shed new light on questions that seem to be inaccessible using their semisimple relatives. In order to have potential applications to physics, these non-semisimple categories and TQFTs should possess Hermitian structures. We will define these structures and give some applications.

- - - - Thursday, Feb 23, 2023 - - - -

- - - - Friday, Feb 24, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Friday February 24, 2:00pm-3:30pm, Room 6417

Johanna Franklin, Hofstra University

When Gromov asked 'What is a typical group?', he was thinking of finitely presented groups, and he proposed an approach involving limiting density. Here, we reframe this question in the context of universal algebra and discuss some examples illustrating the behaviors of some of these algebraic varieties and then general conditions that imply some of these behaviors. Our primary general result states that for a commutative generalized bijective variety and presentations with a single generator and single identity, the zero-one law holds and, furthermore, that the sentences with density 1 are those true in the free structure. The proof of this result requires a specialized version of Gaifman's Locality Theorem that enables us to get a better bound on the complexity of the formulas of interest to us.

This work is joint with Meng-Che 'Turbo' Ho and Julia Knight.

Next Week in Logic at CUNY:

- - - - Monday, Feb 27, 2023 - - - -

Logic and Metaphysics Workshop

Date: Monday, February 27, 4.15-6.15pm (NY time), GC room TBD

NOTE: Meetings this semester are in person only (no zoom)

For meeting information, please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Lionel Shapiro, UConn

- - - - Tuesday, Feb 28, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 28, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)**Zuzana Hanikova**, Czech Academy of Sciences

**Vopěnka's Alternative Set Theory and its mathematical context**

Vopěnka first presented his Alternative Set Theory (AST) in the monograph 'Mathematics in the Alternative Set Theory' published by Teubner, Leipzig in 1979. Another book presenting the theory, 'Introduction to Mathematics in the Alternative Set Theory', was published in 1989 in Slovak by Alfa, Bratislava. In addition there are numerous journal papers on the AST by members of the research group established by Vopěnka, and the proceedings of a conference dedicated to the AST, also from 1989. In several essays, Vopěnka sought to lay out the motivation and philosophical import of the AST and some of his subsequent work. As one consequence of the emphasis on his philosophy, the mathematical inspiration for the AST has been somewhat obliterated. The aim of the talk is to discuss the design choices Vopěnka made for the AST in relation to pertinent mathematical developments of the 20th century, such as Skolem's work on nonstandard models of arithmetic, Robinson's nonstandard analysis, Rieger's nonstandard models of arithmetic, Vopěnka's nonstandard model of set theory, Vopěnka and Hájek's theory of semisets, or Parikh's almost consistent theories. The presentation will include an outline of the AST following the works of Vopěnka and Sochor. This is a historical talk; no new mathematical results on the AST will be presented.

- - - - Wednesday, Mar 1, 2023 - - - -

- - - - Thursday, Mar 2, 2023 - - - -

- - - - Friday, Mar 3, 2023 - - - -

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

2/19/2023 10:44:12

Dear all,
The seminar meets on Wednesday February 22nd at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jonathan Cancino Manriquez -- Maximal trees on P(omega)/fin
Given a partial order (P,<), a tree T on P is a subset of P such that T
order by the inverse order defined by <, is a tree. This notion was
introduced by D. Monk some years ago, and asked about the size of
maximal trees on [omega]^omega order by almost inclusion. In this talk
we will review some constructions of maximal trees of cardinality
omega_1 under some parametrized diamond principles and some related
results. This is joint work with G. Campero, M. Hrusak and F. Miranda.
Best,
David

## Barcelona Set Theory Seminar

Barcelona Logic Seminar

2/18/2023 16:01:35

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: On Disjoint Stationary Sequences

DATE: Wednesday, 22 February 2023

TIME: 16:00 (CET)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

## Logic Seminar Wed 15 Feb 2023 17:00 hrs at NUS by David Belanger

NUS Logic Seminar

2/14/2023 18:19:12

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 15 February 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#05-11
Speaker: David Belanger
Title: A system of functionals-of-finite-type for BSigma_n models
Abstract:
We present a system of functionals that can serve as Skolem functions,
so that any arithmetical formula can be rewritten in terms of them, in
a model of BSigma_n + not ISigma_n. A distinguishing feature of our
construction is that each functional is coded as a natural number
within the model, and there is an upper bound on the codes. The method
has a number of interesting applications.
This is joint work with Chong, Li, Wong and Yang.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Nankai Logic Colloquium

Nankai Logic Colloquium

2/13/2023 5:42:19

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Riccardo Camerlo from University of Genoa. This talk is going to take place this Friday, Feb.17, 2023, from 4 pm to 5 pm (UTC+8, Beijing time).

Title: On some reducibility hierarchies
Abstract:
The notion of reducibility allows to compare sets or, more generally,
relations by using a given class of functions to make the comparison.
The choice of different classes of functions may give rise to very
diffent hierarchies.
Purpose of the talk is to give an elementary presentation of some of
these hierarchies, discuss some examples, and comment on some open
problems.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 16th Nankai Logic Colloquium --Riccardo Camerlo

Time： 16:00pm, Feb. 17, 2023 (Beijing Time)

Zoom Number：839 6396 1742

Passcode： 321054

Link： https://zoom.us/j/83963961742?pwd=c2ppSXpMQks3Vit5bnZkUm5heElNUT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/12/2023 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Feb 13, 2023 - - - -

Rutgers Logic Seminar

Monday, February 13, 2pm, Rutgers University, Hill 005

James Holland, Rutgers

Forcing more choice over the Chang model

- - - - Tuesday, Feb 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 14, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id) Vladimir Kanovei, Institute for Information Transmission Problems

**On the significance of parameters in the choice and сomprehension schemata in the 2nd-order Peano arithmetic**

Parameters are free variables in various axiom schemata in PA, ZFC, and other similar theories. Given an axiom schema S, we let S* be the parameter-free sub-schema.

Kreisel (A survey of proof theory, JSL 1968) was one of those who paid attention to the comparison of some schemata in second-order PA and their parameter-free versions. In particular, Kreisel noted that

[...] if one is convinced of the significance of something like a given axiom schema, it is natural to study details, such as the effect of parameters.This talk is devoted to the effect of parameters in the schemata of Comprehension and Choice in second-order arithmetic.

- - - - Wednesday, Feb 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, Second Lecture.

Speaker: ** Mee Seong Im, United States Naval Academy, Annapolis.**

Date and Time: ** Wednesday February 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Automata and topological theories.**

Abstract: Theory of regular languages and finite state automata is part of the foundations of computer science. Topological quantum field theories (TQFT) are a key structure in modern mathematical physics. We will interpret a nondeterministic automaton as a Boolean-valued one-dimensional TQFT with defects labelled by letters of the alphabet for the automaton. We will also describe how a pair of a regular language and a circular regular language gives rise to a lax one-dimensional TQFT.

- - - - Thursday, Feb 16, 2023 - - - -

- - - - Friday, Feb 17, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Friday February 17, 2:00pm-3:30pm, Room 6417

**Russell Miller**, CUNY

**Computability and the Absolute Galois Group of Q**

Fix a computable presentation ¯¯¯¯Q of the algebraic closure of the rational numbers. The absolute Galois group of the rational numbers, which is precisely the automorphism group of the field ¯¯¯¯Q, may then be viewed as a collection of paths through a finite-branching tree. Each individual automorphism has a Turing degree. We will use known results in computability to try to build natural countable elementary subgroups of the absolute Galois group. Several intriguing questions in number theory will appear as we measure the extent to which we succeed in doing so.

Next Week in Logic at CUNY:

- - - - Monday, Feb 20, 2023 - - - -

- - - - Tuesday, Feb 21, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 21, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Alexei Miasnikov, Stevens Institute of Technology

**First-order classification and non-standard models**

In this talk I will discuss some recent advances in the first-order classification problem. I will touch on first-order rigidity and quasi finite axiomatization. However, the main point of the presentation is on how, in principle, one can describe all structures which are first-order equivalent to a given one. This leads to non-standard models of algebraic structures (aka non-standard analysis or non-standard arithmetic), which are interesting in their own right.

- - - - Wednesday, Feb 22, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, **Third Lecture.**

Speaker: Joshua Sussan, **CUNY.**

Date and Time: ** Wednesday February 22, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Non-semisimple Hermitian TQFTs.**

Abstract: Topological quantum field theories coming from semisimple categories build upon interesting structures in representation theory and have important applications in low dimensional topology and physics. The construction of non-semisimple TQFTs is more recent and they shed new light on questions that seem to be inaccessible using their semisimple relatives. In order to have potential applications to physics, these non-semisimple categories and TQFTs should possess Hermitian structures. We will define these structures and give some applications.

- - - - Thursday, Feb 23, 2023 - - - -

- - - - Friday, Feb 24, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Friday February 24, 2:00pm-3:30pm, Room 6417

Johanna Franklin, Hofstra University

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

2/12/2023 14:15:49

Dear all,
The seminar meets on Wednesday February 15th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Chris Lambie-Hanson -- Whitehead's problem, expanded and
condensed, Part 2
Whitehead's problem, which asks whether every Whitehead group is a free
abelian group, was a prominent open question in group theory in the
mid-20th century. In 1974, Shelah proved that the problem is independent
of ZFC: if V=L, then every Whitehead group is free, whereas if Martin's
Axiom and the negation of CH hold, then there is a non-free Whitehead
group. This was a major surprise and was one of the first major problems
coming from outside logic and set theory to be proven to be independent.
Last week, we sketched a proof of Shelah's independence result. This
week, we present some more recent work, focusing on the category of
condensed abelian groups, introduced recently by Clausen and Scholze as
an enrichment of the category of topological abelian groups with nicer
algebraic properties. We will give a new, concrete, combinatorial proof
of a result, due to Clausen and Scholze, stating that Whitehead's
problem is not independent in the category of condensed abelian groups.
We will end by using some of the ideas of this proof to highlight some
potential connections between condensed mathematics and the theory of
forcing.
Best,
David

## Barcelona Set Theory Seminar

Barcelona Logic Seminar

2/8/2023 3:52:44

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: Andreas Lietz

TITLE:** **Forcing "NS is

_{1}-Dense"
from Large Cardinals

DATE: Wednesday, 15 February 2023

TIME: 16:00 (CET)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat

bagaria@ub.edu

## Nankai Logic Colloquium

Nankai Logic Colloquium

2/8/2023 3:47:59

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Anush Tserunyan from McGill University. This talk is going to take place this Friday, Feb.10, 2023, from 4 pm to 5 pm (UTC+8, Beijing time).

**Title.** A descriptive approach to pointwise ergodic theorems

**Abstract.** Pointwise ergodic theorems provide a bridge between the global behaviour of the dynamical system and the local combinatorial statistics of the system at a point. These theorems are powerful tools used in ergodic theory, probability, number theory, and other areas of mathematics. I will describe a new general yet elementary approach for proving such theorems, which is inspired by descriptive set theory. This approach has led to new kinds of pointwise ergodic theorems, and I will discuss those obtained in joint work with Jenna Zomback.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 15th Nankai Logic Colloquium --Anush Tserunyan

Time： 16:00pm, Feb. 10, 2023 (Beijing Time)

Zoom Number：836 2979 3119

Passcode： 476294

Link： https://us02web.zoom.us/j/83629793119?pwd=R1c4OHJReXNMTHE2dFpOOS91bnhQUT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## Logic Seminar Wed 8 Feb 2023 17:00 hrs at NUS via Zoom by Will Johnson

NUS Logic Seminar

2/6/2023 21:16:09

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 8 February 2023, 17:00 hrs
Talk via Zoom:
https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
Meeting ID: 830 4925 8042
Passcode: 1729=x3+y3
Speaker: Will Johnson
Title: NIP integral domains and Henselianity
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
Abstract:
Is every NIP integral domain a Henselian local ring?
In this talk, I will give evidence for this conjecture,
sketching why it holds in the positive characteristic
case and the finite dp-rank case. I will also discuss
how this ``generalized Henselianity conjecture''
is related to the standard conjectures on NIP fields
and valued fields. For example, the Henselianity
conjecture for NIP valued fields implies the
generalized Henselianity conjecture for Noetherian NIP
integral domains.
Lastly I will discuss how this conjecture fits
into the general problem of classifying NIP fields
and NIP commutative rings. For example, it implies
that NIP fields with definable field topologies
must be ample/large in the sense of Pop, and
NIP commutative rings must be finite products
of Henselian local rings.

## UPDATE: This Week in Logic at CUNY

This Week in Logic at CUNY

2/6/2023 10:18:34

Hi everyone,

Note the updated email for Victoria Gitman throughout the newsletter below - please use her updated address

vgitman@gmail.com**.**

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Feb 6, 2023 - - - -

Rutgers Logic Seminar

Monday, February 6, 2pm, Rutgers University, Hill 005

Brian Pinsky, Rutgers

Hopfian groups are complete co-analytic

- - - - Tuesday, Feb 7, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 7, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Mikhail Katz, Bar Ilan University

**Effective infinitesimals in R**

We survey the effective foundations for analysis with infinitesimals recently developed by Hrbacek and Katz, and detail some applications. Theories SPOT and SCOT illustrate the fact that analysis with infinitesimals requires no more choice than traditional analysis. The theory SCOT incorporates in particular all the axioms of Nelson's Radically Elementary Probability Theory, which is therefore conservative over ZF+ADC.

- - - - Wednesday, Feb 8, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, First Lecture.

Speaker: ** Mikhail Khovanov, Columbia University.**

Date and Time: ** Wednesday February 8, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Universal construction and its applications.**

Abstract: Universal construction starts with an evaluation of closed n-manifolds and builds a topological theory (a lax TQFT) for n-cobordisms. A version of it has been used for years as an intermediate step in constructing link homology theories, by evaluating foams embedded in 3-space. More recently, universal construction in low dimensions has been used to find interesting structures related to Deligne categories, formal languages and automata. In the talk we will describe the universal construction and review these developments.

- - - - Thursday, Feb 9, 2023 - - - -

- - - - Friday, Feb 10, 2023 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, February 10, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@gmail.com) for meeting id. Davide Leonessi CUNY

**Strategy and determinacy in infinite Hex**

The popular game of Hex can be extended to the infinite hexagonal lattice, defining a winning condition which formalises the idea of a chain of colored stones stretching towards infinity. The descriptive-set-theoretic complexity of the set of winning positions is unknown, although it is at most Σ^1_1, and it is conjectured to be Borel; this has implications on whether games of infinite Hex are determined from all initial positions as either first-player wins or draws.

I will show that, unlike the finite game, infinite Hex with an initially empty board is a draw. But is the game still a draw when starting from a non-empty board? This open question can be partially answered in the positive by assuming the existence of certain local strategies, and in the negative by giving the advantage of placing two stones at each turn to one of the players. This is joint work with Joel David Hamkins.

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Friday February 10, 2:00pm-3:30pm, Room 6417

**Athar Abdul-Quader**, Purchase College

**Satisfaction and saturation**

It is well known that a countable model of PA has a truth predicate if and only if it is recursively saturated. It is also well known that not all countable recursively saturated models of PA have *inductive* or even Δ0-inductive truth predicates: indeed, such models must satisfy Con(PA), for example. Recent work by Enayat-Pakhomov and Cieśliński-Łełyk-Wcisło explored the principle of 'disjunctive correctness', asserting that every disjunction is true if and only if it has a true disjunct. In particular, one can show that every countable model of PA has a 'disjunctively trivial' elementary extension: that is, an elementary extension with a truth predicate in which all nonstandard length disjunctions are evaluated as true. In this talk, we will see that such 'disjunctively trivial' models are necessarily arithmetically saturated; indeed, we will see that a countable model of PA is arithmetically saturated if and only if it has a disjunctively trivial truth predicate. We will explore related pathologies in truth predicates, and classify the sets which can be defined using such pathologies. We find other surprising connections between arithmetic saturation and these questions of definability. This is joint work with Mateusz Łełyk, based heavily on unpublished work by Jim Schmerl.

Next Week in Logic at CUNY:

- - - - Monday, Feb 13, 2023 - - - -

Rutgers Logic Seminar

Monday, February 13, 2pm, Rutgers University, Hill 005

James Holland, Rutgers

- - - - Tuesday, Feb 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 14, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id) Vladimir Kanovei, Institute for Information Transmission Problems

**On the significance of parameters in the choice and сomprehension schemata in the 2nd-order Peano arithmetic**

Parameters are free variables in various axiom schemata in PA, ZFC, and other similar theories. Given an axiom schema S, we let S* be the parameter-free sub-schema.

Kreisel (A survey of proof theory, JSL 1968) was one of those who paid attention to the comparison of some schemata in second-order PA and their parameter-free versions. In particular, Kreisel noted that

[...] if one is convinced of the significance of something like a given axiom schema, it is natural to study details, such as the effect of parameters.This talk is devoted to the effect of parameters in the schemata of Comprehension and Choice in second-order arithmetic.

- - - - Wednesday, Feb 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, First Lecture.

Speaker: ** Mee Seong Im, United States Naval Academy, Annapolis.**

Date and Time: ** Wednesday February 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Automata and topological theories.**

Abstract: Theory of regular languages and finite state automata is part of the foundations of computer science. Topological quantum field theories (TQFT) are a key structure in modern mathematical physics. We will interpret a nondeterministic automaton as a Boolean-valued one-dimensional TQFT with defects labelled by letters of the alphabet for the automaton. We will also describe how a pair of a regular language and a circular regular language gives rise to a lax one-dimensional TQFT.

- - - - Thursday, Feb 16, 2023 - - - -

- - - - Friday, Feb 17, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Friday February 17, 2:00pm-3:30pm, Room 6417

**Russell Miller**, CUNY

**Computability and the Absolute Galois Group of Q**

Fix a computable presentation ¯¯¯¯Q of the algebraic closure of the rational numbers. The absolute Galois group of the rational numbers, which is precisely the automorphism group of the field ¯¯¯¯Q, may then be viewed as a collection of paths through a finite-branching tree. Each individual automorphism has a Turing degree. We will use known results in computability to try to build natural countable elementary subgroups of the absolute Galois group. Several intriguing questions in number theory will appear as we measure the extent to which we succeed in doing so.

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/5/2023 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Feb 6, 2023 - - - -

Rutgers Logic Seminar

Monday, February 6, 2pm, Rutgers University, Hill 005

Brian Pinsky, Rutgers

Hopfian groups are complete co-analytic

- - - - Tuesday, Feb 7, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 7, 1:00pmVirtual (email Victoria Gitman vgitman@nylogic.org for meeting id)Mikhail Katz, Bar Ilan University

**Effective infinitesimals in R**

We survey the effective foundations for analysis with infinitesimals recently developed by Hrbacek and Katz, and detail some applications. Theories SPOT and SCOT illustrate the fact that analysis with infinitesimals requires no more choice than traditional analysis. The theory SCOT incorporates in particular all the axioms of Nelson's Radically Elementary Probability Theory, which is therefore conservative over ZF+ADC.

- - - - Wednesday, Feb 8, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, First Lecture.

Speaker: ** Mikhail Khovanov, Columbia University.**

Date and Time: ** Wednesday February 8, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Universal construction and its applications.**

Abstract: Universal construction starts with an evaluation of closed n-manifolds and builds a topological theory (a lax TQFT) for n-cobordisms. A version of it has been used for years as an intermediate step in constructing link homology theories, by evaluating foams embedded in 3-space. More recently, universal construction in low dimensions has been used to find interesting structures related to Deligne categories, formal languages and automata. In the talk we will describe the universal construction and review these developments.

- - - - Thursday, Feb 9, 2023 - - - -

- - - - Friday, Feb 10, 2023 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, February 10, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id. Davide Leonessi CUNY

**Strategy and determinacy in infinite Hex**

The popular game of Hex can be extended to the infinite hexagonal lattice, defining a winning condition which formalises the idea of a chain of colored stones stretching towards infinity. The descriptive-set-theoretic complexity of the set of winning positions is unknown, although it is at most Σ^1_1, and it is conjectured to be Borel; this has implications on whether games of infinite Hex are determined from all initial positions as either first-player wins or draws.

I will show that, unlike the finite game, infinite Hex with an initially empty board is a draw. But is the game still a draw when starting from a non-empty board? This open question can be partially answered in the positive by assuming the existence of certain local strategies, and in the negative by giving the advantage of placing two stones at each turn to one of the players. This is joint work with Joel David Hamkins.

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Friday February 10, 2:00pm-3:30pm, Room 6417

**Athar Abdul-Quader**, Purchase College

**Satisfaction and saturation**

It is well known that a countable model of PA has a truth predicate if and only if it is recursively saturated. It is also well known that not all countable recursively saturated models of PA have *inductive* or even Δ0-inductive truth predicates: indeed, such models must satisfy Con(PA), for example. Recent work by Enayat-Pakhomov and Cieśliński-Łełyk-Wcisło explored the principle of 'disjunctive correctness', asserting that every disjunction is true if and only if it has a true disjunct. In particular, one can show that every countable model of PA has a 'disjunctively trivial' elementary extension: that is, an elementary extension with a truth predicate in which all nonstandard length disjunctions are evaluated as true. In this talk, we will see that such 'disjunctively trivial' models are necessarily arithmetically saturated; indeed, we will see that a countable model of PA is arithmetically saturated if and only if it has a disjunctively trivial truth predicate. We will explore related pathologies in truth predicates, and classify the sets which can be defined using such pathologies. We find other surprising connections between arithmetic saturation and these questions of definability. This is joint work with Mateusz Łełyk, based heavily on unpublished work by Jim Schmerl.

Next Week in Logic at CUNY:

- - - - Monday, Feb 13, 2023 - - - -

Rutgers Logic Seminar

Monday, February 13, 2pm, Rutgers University, Hill 005

James Holland, Rutgers

- - - - Tuesday, Feb 14, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, February 14, 1:00pmVirtual (email Victoria Gitman vgitman@nylogic.org for meeting id)Vladimir Kanovei, Institute for Information Transmission Problems

**On the significance of parameters in the choice and сomprehension schemata in the 2nd-order Peano arithmetic**

Parameters are free variables in various axiom schemata in PA, ZFC, and other similar theories. Given an axiom schema S, we let S* be the parameter-free sub-schema.

Kreisel (A survey of proof theory, JSL 1968) was one of those who paid attention to the comparison of some schemata in second-order PA and their parameter-free versions. In particular, Kreisel noted that

[...] if one is convinced of the significance of something like a given axiom schema, it is natural to study details, such as the effect of parameters.This talk is devoted to the effect of parameters in the schemata of Comprehension and Choice in second-order arithmetic.

- - - - Wednesday, Feb 15, 2023 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Special Topic: ** **__TQFT and Computation__, First Lecture.

Speaker: ** Mee Seong Im, United States Naval Academy, Annapolis.**

Date and Time: ** Wednesday February 15, 2023, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** Automata and topological theories.**

Abstract: Theory of regular languages and finite state automata is part of the foundations of computer science. Topological quantum field theories (TQFT) are a key structure in modern mathematical physics. We will interpret a nondeterministic automaton as a Boolean-valued one-dimensional TQFT with defects labelled by letters of the alphabet for the automaton. We will also describe how a pair of a regular language and a circular regular language gives rise to a lax one-dimensional TQFT.

- - - - Thursday, Feb 16, 2023 - - - -

- - - - Friday, Feb 17, 2023 - - - -

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Friday February 17, 2:00pm-3:30pm, Room 6417

**Russell Miller**, CUNY

**Computability and the Absolute Galois Group of Q**

Fix a computable presentation ¯¯¯¯Q of the algebraic closure of the rational numbers. The absolute Galois group of the rational numbers, which is precisely the automorphism group of the field ¯¯¯¯Q, may then be viewed as a collection of paths through a finite-branching tree. Each individual automorphism has a Turing degree. We will use known results in computability to try to build natural countable elementary subgroups of the absolute Galois group. Several intriguing questions in number theory will appear as we measure the extent to which we succeed in doing so.

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

2/4/2023 7:24:17

Dear all,
The seminar meets on Wednesday February 8th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Chris Lambie-Hanson -- Whitehead's problem, expanded and condensed
Whitehead's problem, which asks whether every Whitehead group is a free
abelian group, was a prominent open question in group theory in the
mid-20th century. In 1974, Shelah proved that the problem is independent
of ZFC: if V=L, then every Whitehead group is free, whereas if Martin's
Axiom and the negation of CH hold, then there is a non-free Whitehead
group. This was a major surprise and was one of the first major problems
coming from outside logic and set theory to be proven to be independent.
In recent years, Clausen and Scholze have introduced the category of
condensed abelian groups, which can be seen as an enrichment of the
category of topological abelian groups with nicer algebraic properties.
Through some deep structural analysis of this category, they showed
that, when appropriately interpreted, Whitehead's problem is not
independent in the category of condensed abelian groups; it is provable
in ZFC that every abelian group that is Whitehead in the condensed
category must be free. In the first half of the talk, we will introduce
Whitehead's problem and provide a sketch of Shelah's proof. In the
second half, we will give a new, concrete, combinatorial proof of
Clausen and Scholze's result. No knowledge of algebra will be assumed of
the audience; all proofs will involve only set theoretic techniques and
very basic group theory.
Best,
David

## CMU math logic seminar next Tuesday

Carnegie Mellon Logic Seminar

2/2/2023 10:12:06

TUESDAY, February 7, 2023

Mathematical Logic Seminar: 3:30-4:30 PM Eastern,

**Online**, Tom Benhamou, University of Illinois at Chicago

Join Zoom Meeting:

https://cmu.zoom.us/j/92655324096?pwd=VUhSSlkrdHMxbTlSYUMxYzFXM01kdz09Meeting ID: 926 5532 4096

Passcode: 555455

TITLE: Saturation properties of ultrafilters

ABSTRACT: In this talk, we will focus on certain saturation properties of filters and ultrafilters which generalizes the so-called Galvin property. In the first part of the talk, we will present a connection between such ultrafilters and the existence of Slim-Kurepa trees. We will then present several results regarding the existence of non-Galvin ultrafilters under several large cardinal assumptions. Finally, if time permits, we will present a recent application to canonical inner models and some open related questions.

## Core model seminar next Tuesday

Carnegie Mellon Logic Seminar

2/2/2023 10:16:42

ABSTRACT: We discuss the inner model C(aa) introduced by Kennedy-Magidor-Väänänen, and answer several questions posed in their paper "Inner models from strong logics". Assuming large cardinal axioms, we'll show that this model satisfies GCH (this is joint work with John Steel) and that C(aa) satisfies o(κ) = κ^{++} for all regular cardinals κ > ω_{1} (this is joint work with Otto Rajala).

## Logic Seminar 1 Feb 2023 17:00 hrs at NUS by Yu Liang, Nanjing University

NUS Logic Seminar

1/27/2023 0:29:50

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 1 February 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#05-11
Speaker: Yu Liang
Title: Some applications of recursion theory to set theory
Abstract: I shall present some recent results in set theory
which are based on proof methods and results from recursion theory.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Reminder for today's Talk

NUS Logic Seminar

1/25/2023 3:49:53

The following logic semianr talk is today (now) at 17:00 hrs
Singapore time; the talk is only by Zoom.
The Zoom Login is this:
https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
Meeting ID: 830 4925 8042
Passcode: 1729=x3+y3
Title and Abstract of today's talk can be found on the
following webpage of the logic seminar:
https://www.comp.nus.edu.sg/~fstephan/logicseminar.html
The title is: Regressive versions of Hindman's Theorem.
The speaker is: Leonardo Mainardi.
You find on this link also the still free time-slots; if any of
you wants to give a talk from overseas, we will make it on Zoom
as well; local speakers can also give a physical talk in the
meeting.
Best regards, Frank

## Cross-Alps Logic Seminar (speaker: Katarzyna Kowalik)

Cross-Alps Logic Seminar

1/23/2023 4:58:04

On Friday 27.01.2023 at 16:00

**Katarzyna Kowalik** (University of Warsaw)will give a talk on

*Reverse mathematics of some Ramsey-theoretic principles over a weak base theory*Please refer to the usual webpage of our

LogicGroup for more details and the abstract of the talk.

The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

## This Week in Logic at CUNY

This Week in Logic at CUNY

1/22/2023 22:30:00

The CUNY semester starts this week - welcome back, everyone! I want to draw particular attention to the Fitting at 80 Conference taking place this Saturday, January 28th (see below for details).

Best,

Jonas Reitz

This Week in Logic at CUNY:

- - - - Monday, Jan 23, 2023 - - - -

Rutgers Logic Seminar

Monday, January 23, 2pm, Rutgers University, Hill 005

Chris Laskowski (University of Maryland)

The Borel complexity of modules

- - - - Tuesday, Jan 24, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, January 24, 1:00pmVirtual (email Victoria Gitman vgitman@nylogic.org for meeting id)Karel Hrbacek, CUNY

**Representation of unlimited integers**

Nonstandard methods have been successfully applied to standard problems in number theory by R. Jin, T. Tao and others. A. Boudaoud and D. Bellaouar are pursuing the opposite direction: they are formulating number-theoretic problems in the language of nonstandard analysis and solving them by standard methods. Two examples of the kind of questions they consider are:

(1) Can every unlimited natural number n be represented in the form n = s + w_1w_2 where s is a limited integer and w_1, w_2 are unlimited?

(2) Can every unlimited natural number n be represented in the form n = w_1w_2 + w_3w_4 so that each ratio w_i / w_j is appreciable (ie, neither infinitesimal nor unlimited)?

I give a negative answer to question (1) (assuming Dickson’s Conjecture) and a positive answer to question (2).

A. Boudaoud, D. Bellaouar, Representation of integers: A nonclassical point of view, Journal of Logic & Analysis. 12:4 (2020) 1{31; K. Hrbacek, Journal of Logic & Analysis 12:5 (2020) 1–6.

- - - - Wednesday, Jan 25, 2023 - - - -

- - - - Thursday, Jan 26, 2023 - - - -

- - - - Friday, Jan 27, 2023 - - - -

- - - - Saturday, Jan 28, 2023 - - - -

**Fitting at 80**Saturday, January 28

A prominent logician Melvin Fitting has turned 80. This online conference is a special event in his honor. Melvin Fitting was in the departments of Computer Science, Philosophy, and Mathematics at the CUNY Graduate Center and in the department of Mathematics and Computer Science at Lehman College. He is now Professor Emeritus. He has authored 11 books and over a hundred research papers with staggering citation figures. In 2012 Melvin Fitting was given the Herbrand Award by the Conference on Automated Deduction (CADE) for distinguished contributions to the field.

Greetings, congratulations, photos for posting, and ZOOM link requests could be sent to Sergei Artemov by

sartemov@gmail.com or

sartemov@gc.cuny.edu.

Conference website

https://sartemov.ws.gc.cuny.edu/fitting-at-80/Program (the times are given in the Eastern Day Time zone EST).

January 28, Saturday

8:00-8:45 am Arnon Avron (Tel Aviv), “Breaking the Tie: Benacerraf’s Identification Argument Revisited”

8:45-9:30 am Junhua Yu (Beijing), "Exploring Operators on Neighborhood Models"

9:45-10:30 am Sara Negri (Genoa), "Faithful Modal Embedding: From Gödel to Labelled Calculi"

10:30-11:15 am Heinrich Wansing (Bochum), “Remarks on Semantic Information and Logic. From Semantic Tetralateralism to the Pentalattice 65536_5”

11:30 am -12:15 pm Roman Kuznets (Vienna), "On Interpolation"

12:15-1:00 pm Walter Carnielli (Campinas), “Combining KX4 and S4: A Logic That Encompasses Factive and Non-factive Evidence”

1:15-2:00 pm Eduardo Barrio and Federico Pailos (Buenos Aires), “Meta-classical Non-classical Logics”

2:00-2:45 pm Graham Priest (New York), "Jaśkowski and the Jains: a Fitting Tribute"

2:45-4:00 pm Session of memories and congratulations featuring Sergei Artemov, Hiroakira Ono, Anil Nerode, Melvin Fitting, and others.

Next Week in Logic at CUNY:

- - - - Monday, Jan 30, 2023 - - - -

- - - - Tuesday, Jan 31, 2023 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, January 31, 1:00pmVirtual (email Victoria Gitman vgitman@nylogic.org for meeting id)**Lorenzo Galeotti**, Amsterdam University College

**Order types of models of arithmetic without induction**

It is a well-known fact that non-standard models of Peano Arithmetic (PA) have order type N + Z · D, where D is a dense linear order. The question of which dense linear orders D can occur in such order types is non-trivial and widely studied. In this context Friedman asked the following question:

Are there consistent extensions of Peano Arithmetic T and T′ such that the class of order types of models of T and the class of order types of models of T′ differ?

Friedman’s question is very complex and still wide open. In this talk we will go in the opposite direction and consider a version of Friedman’s question for syntactic fragments of PA. We will present results from a joint work with Benedikt Löwe on order types of non-standard models of syntactic subsystems of arithmetic obtained by restricting the language to subsets of the operations. We will put particular emphasis on models of syntactic subsystems of Peano Arithmetic obtained by dropping the schema of induction.

- - - - Wednesday, Feb 1, 2023 - - - -

- - - - Thursday, Feb 2, 2023 - - - -

- - - - Friday, Feb 3, 2023 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, February 3, 12:30pm NY timeVirtual: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id. Jing Zhang, University of Toronto

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

1/22/2023 17:07:37

Dear all,
The seminar meets on Wednesday January 25th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: David Bradley-Williams -- Limits of betweenness relations and
their automorphism groups
Some permutation groups are best represented/constructed as
kinds-of-products of or limits of simpler permutation groups. We discuss
joint work with John Truss (Leeds) in which we construct a family of
structures called "limits of betweenness relations" as a kind of
tree-limit of trees (for appropriate combinatorial meanings of the word
"tree"). A crucial part of the construction is an particular instance of
categorical Fraissé Theory. Further we plan to say how their
automorphism groups fit into the landscape of infinite primitive Jordan
permutation groups and the structure theory of Jordan groups established
by S. Adeleke, D. Macpherson, and P. M. Neumann.
Best,
David
PS: Let me also remind you the joint Logic Seminar/Colloquium of the
MLTCS department on Monday January 23rd, 16:00, Institute of Mathematics
CAS, blue lecture room on the ground floor of the rear building. After
the lecture we will go to a pub.
Niel Thapen -- Bounded arithmetic and witnessing
A witnessing theorem lets you recover, from a proof that an object
exists, an algorithm to construct such an object. I will introduce the
weak arithmetic theory S^1_2 and describe a simple model-theoretic proof
of Buss's witnessing theorem, connecting this theory with polynomial
time computations, with some unprovability results that follow from
this. I will discuss some open problems about witnessing for stronger
bounded theories.

## (KGRC) guests, video, and a talk on Thursday, January 26

Kurt Godel Research Center

1/19/2023 12:21:04

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31 and
gives a talk on January 26, see below.
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31.
Jonathan Schilhan (host: Thilo Weinert) visits the KGRC until January 31.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August 15.
Jerzy Kąkol (host: Damian Sobota) visits the KGRC from February 27 to March 3.
Manuel López Pellicer (host: Damian Sobota) visits the KGRC from February 27 to
March 3.
Juris Steprāns (host: Vera Fischer) visits the KGRC from March 6 to March 10
and gives a two-part talk, details to be announced at a later time.
* * *
For some seminar talks, video recordings are available:
"Introduction to big Ramsey degrees" by David Chodounský:
https://univienna.zoom.us/rec/share/he-aDDiZDHZJ8Y4Zn_FjiIwdbOf0VN6UKJrxWC7xXAEf6CG_k6Cu_QfM3gQGzwsd.wYq8tUjxaZFywaFK
Pass code: @&61nNnR
"The weak Ramsey property" by Wiesław Kubiś:
https://univienna.zoom.us/rec/share/VeLRgmK7tBdTUOLxgzKjPhh20ErRsjUWp7v6hkNpZtM9Gxe3Xu73_Cc_iTF_AYpL.zDpkipMb7P_vKHwO
Pass code: +MkI4HUc
"A weak form of Global Choice under the GCH, part II" by Peter Holy:
https://univienna.zoom.us/rec/share/xVaRaaDknVfPsyI6D_XZtFsxMjHr8bYSXbup0r6knM3oojoSAFdjipHgPOzN5jVw.8N-UyUkiL2g_6IJj
Pass code: gS3%+Hy2
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, January 26
"Lang-Weil type bounds in finite difference fields"
Martin Hils (Universität Münster, DE)
We establish Lang-Weil type bounds for the number of rational points of
difference varieties over finite difference fields, in terms of the transformal
dimension of the variety and assuming the existence of a smooth rational point.
It follows that, working in any non-principle ultraproduct $K$ of finite
difference fields, the normalized pseudofinite dimension of a quantifier free
partial type $p$ is equal to the transformal dimension of $p$, i.e., to the
maximal transformal transcendence degree over $K$ of a realization of $p$.
This is joint work with Ehud Hrushovski, Jinhe Ye and Tingxiang Zou.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at Uni
Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom: If you need the Zoom data and have not received the meeting link by
the day before the talk, please contact richard.springer@univie.ac.at!
(Please direct any other requests about the Zoom session to
vera.fischer@univie.ac.at.)

## Logic Seminar Wed 18 Jan 2023 17:00 hrs at NUS by Bakhadyr Khoussainov

NUS Logic Seminar

1/18/2023 4:12:18

Hello, there was a mistake, the talk is only in Zoom.
Please use this login (also below):
> > Link to join the Zoom Meeting
> > https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
> >
> > Meeting ID: 830 4925 8042
> > Passcode: 1729=x3+y3
Sorry for the confusion caused. Regards, Frank Stephan
On Thu, Jan 12, 2023 at 03:01:35PM +0800, Frank STEPHAN wrote:
> Invitation to the Logic Seminar at the National University of Singapore
>
> Date: Wednesday, 18 January 2022, 17:00 hrs
>
> Place: NUS, Department of Mathematics, S17#04-05
> Talk via Zoom:
> https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
> Meeting ID: 830 4925 8042
> Passcode: 1729=x3+y3
>
> Speaker: Bakhadyr Khoussainov
>
> Title: Definability of algorithmically presented structures.
>
> URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
>
> We aim to describe the isomorphism types of algorithmically
> presented structures in the language of the first order logic.
> This is one of the key research topics related to the expressive
> power of the first order logic. The focus is on two classes
> of structures. The first class is the class of structures for
> which the positive atomic diagrams are computably enumerable.
> We call these structures positive structures. The second class
> is the class of structures for which the negative atomic diagrams
> are computably enumerable. We call these structures negative
> structures. We investigate definability of positive and negative
> structures by sets of sentences quantified with Existential,
> Universal, Existential-Universal and Universal-Existential
> quantifiers using expansions of languages.
>

## Descriptive Set Theory and Dynamics: August 14-25, 2023

Conference

1/17/2023 20:37:12

In August 2023 a workshop and a conference on descriptive set theory and dynamics will take place in Warsaw:
Workshop (14-18.08.2023, Warsaw)
Conference (21-25.08.2023, Warsaw)
Both are organized within the thematic semester STRUCTURES devoted to various areas of foundations of mathematics and computer science
https://www.impan.pl/en/activities/banach-center/conferences/23-simons-08

Tagged: Dana Bartošová, Anton Bernshteyn, Filippo Calderoni, Ruiyuan Chen, Michal Doucha, Joshua Frish, Su Gao, Łukasz Grabowski, Jan Grebík, Alexander Kechris, Gábor Kun, Aleksandra Kwiatkowska, François Le Maître, Aristotelis Panagiotopoulos, Oleg Pikhurko, Assaf Shani, Konstantin Slutsky, Sławomir Solecki, Ádám Timár, Todor Tsankov, Spencer Unger, Zoltán Vidnyánszky, Andrew Zucker, Matthew Foreman, Yonatan Gutman, Todor Tsankov, Anush Tserunyan, Shaun Allison, Matthew Bowen, Colin Jahel, Forte Shinko, Grigory Terlov, Riley Thornton, Felix Weilacher, Konrad Wrobel

## CMU Math Logic Seminar next Tuesday

Carnegie Mellon Logic Seminar

1/17/2023 12:37:12

TUESDAY, January 24, 2023
Mathematical Logic Seminar: 3:30-4:30 PM Eastern, Online, Paolo Marimon,
Imperial College London
Join Zoom Meeting:
https://cmu.zoom.us/j/92655324096?pwd=VUhSSlkrdHMxbTlSYUMxYzFXM01kdz09
Meeting ID: 926 5532 4096
Passcode: 555455
TITLE: Invariant Keisler measures in simple omega-categorical structures
ABSTRACT: We study invariant Keisler measures in the context of
omega-categorical structures. For a first-order structure M, these are
finitely additive probability measures on the Boolean algebra of definable
subsets Def_x(M) which are invariant under the action of the automorphism
group Aut(M). A natural notion of smallness for a definable subset of M is
that it is assigned measure 0 by any invariant Keisler measure. Another
natural model-theoretic notion of smallness is forking over the empty set.
These two notions coincide in various classes of structures, including
stable and NIP omega-categorical ones. In a recent article, Chernikov,
Hrushovski, Kruckman, Krupinski, Moconja, Pillay and Ramsey find the first
examples of simple structures with formulas which do not fork over the
empty set but are universally measure zero. I give the first known simple
omega-categorical examples exhibiting this property. These are various
omega-categorical Hrushovski constructions. In order to prove this, I use
a probabilistic independence result by Jahel and Tsankov to show that a
stronger version of the independence theorem holds for simple
omega-categorical structures where a formula forks over the empty set if
and only if it is universally measure zero.

## Wednesday seminar

Prague Set Theory Seminar

1/15/2023 16:33:35

Dear all,
The seminar meets on Wednesday January 18th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
There will be a joint Logic Seminar/Colloquium of the MLTCS department
on Monday January 23rd, 16:00, Institute of Mathematics CAS, blue
lecture room on the ground floor of the rear building. After the lecture
we will go to a pub. Everybody will be welcome!
Wednesday program:
Adam Bartoš -- Isosceles-free homogeneous metric spaces
While studying metric spaces in the context of Fraïssé theory we have
considered the class of isosceles-free metric spaces: the spaces
containing no nondegenerate isosceles triangles. All finite
isoceles-free spaces form a hereditary class without weak amalgamation
property. Every 1-homogeneous isosceles-free space is already
ultrahomogeneous, and we can characterize all such spaces. There are
also related decompositions of metric spaces giving bounds on the
maximal number of distinct distances in a finite ultrahomogeneous metric
space. This is joint work with Christian Bargetz, Wiesław Kubiś, and
Franz Luggin.
MLTCS seminar:
Niel Thapen -- Bounded arithmetic and witnessing
A witnessing theorem lets you recover, from a proof that an object
exists, an algorithm to construct such an object. I will introduce the
weak arithmetic theory S^1_2 and describe a simple model-theoretic proof
of Buss's witnessing theorem, connecting this theory with polynomial
time computations, with some unprovability results that follow from
this. I will discuss some open problems about witnessing for stronger
bounded theories.
Best,
David

## (KGRC) Set Theory Seminar talk on Tuesday, January 17

Kurt Godel Research Center

1/13/2023 10:46:49

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31, 2023
and gives a talk on January 26, 2023 (details to be announced at a later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31, 2023.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August 15.
Tomasz Żuchowski (host: Damian Sobota) visits the KGRC until January 17.
Jerzy Kąkol (host: Damian Sobota) visits the KGRC from February 27 to March 3.
Manuel López Pellicer (host: Damian Sobota) visits the KGRC from February 27 to
March 3.
Juris Steprāns (host: Vera Fischer) visits the KGRC from March 6 to March 10
and gives a two-part talk (details to be announced at a later time).
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, January 17
"A weak form of Global Choice under the GCH, part 2"
Peter Holy (TU Wien)
In 2012, Joel Hamkins asked (on MathOverflow) whether it is possible for the
universe of sets to have a linear ordering, but no wellordering (that is,
global choice fails). This question, which I consider very interesting, appears
to still be open. In my talk, I want to present a somewhat related result.
After providing a gentle introduction to second order set theory and the
principle of global choice (no knowledge on these matters is assumed), we
consider a different weakening of global choice under the GCH: The minimal
ordinal-connection axiom MOC due to Rodrigo Freire. It is equivalent to the
statement that the universe of sets can be stratified by a subset-increasing
hierarchy with each K_alpha of the same size as alpha,
and such that K_kappa=H(kappa), the collection of sets of hereditary size less
than kappa, for every regular infinite cardinal kappa. In this form, it clearly
implies the GCH, and is easily seen to be a weak form of global choice under
the GCH. We will show, using class forcing products of adding Cohen subsets of
regular cardinals (without assuming any particular knowledge regarding the
technique of class forcing), that MOC can consistently fail in models of the
GCH, and that MOC can consistently hold while global choice fails.
This is joint work with Rodrigo Freire (University of Brasilia).
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at Uni
Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom:
If you need the Zoom data and have not received the meeting link by the
day before the talk, please contact richard.springer@univie.ac.at! (Please
direct any other requests about the Set Theory Seminar to
vera.fischer@univie.ac.at.)

## Logic Seminar Wed 18 Jan 2023 17:00 hrs at NUS by Bakhadyr Khoussainov

NUS Logic Seminar

1/12/2023 2:01:35

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 18 January 2022, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Talk via Zoom:
https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09
Meeting ID: 830 4925 8042
Passcode: 1729=x3+y3
Speaker: Bakhadyr Khoussainov
Title: Definability of algorithmically presented structures.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
We aim to describe the isomorphism types of algorithmically
presented structures in the language of the first order logic.
This is one of the key research topics related to the expressive
power of the first order logic. The focus is on two classes
of structures. The first class is the class of structures for
which the positive atomic diagrams are computably enumerable.
We call these structures positive structures. The second class
is the class of structures for which the negative atomic diagrams
are computably enumerable. We call these structures negative
structures. We investigate definability of positive and negative
structures by sets of sentences quantified with Existential,
Universal, Existential-Universal and Universal-Existential
quantifiers using expansions of languages.

## Core Model Seminar starting again in two weeks

Carnegie Mellon Logic Seminar

1/10/2023 13:02:19

TUESDAY, January 24, 2023
Core Model Seminar: 1:30-3 PM Eastern, Online, Takehiko Gappo, TU Wien
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: Chang models over derived models
ABSTRACT: We will give a proof outline of the main theorem in Sargsyan's
paper, "Covering with Chang models over derived models." In this paper, he
constructed a new model of determinacy extending the derived model, called
the Chang model over the derived model, inside of a symmetric extension of
a least branch hod mouse with Woodin cardinals. This result will be used
in the next talk.
TUESDAY, January 31, 2023
Core Model Seminar: 1:30-3 PM Eastern, Online, Takehiko Gappo, TU Wien
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: Determinacy in the Chang model from a hod pair
ABSTRACT: We will show that the Chang model satisfies determinacy from the
existence of an excellent least branch hod pair with a Woodin limit of
Woodin cardinals. The proof is based on Sargsyan's result on Chang models
over derived models. This is joint work with Sargsyan.
TUESDAY, February 7, 2023
Core Model Seminar: 1:30-3 PM Eastern, Online, Gabriel Goldberg,
University of California, Berkeley
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: TBA; ABSTRACT: TBA
TUESDAY, February 14, 2023
Core Model Seminar: 1:30-3 PM Eastern, Online, Gabriel Goldberg,
University of California, Berkeley
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: TBA; ABSTRACT: TBA

## Cross-Alps Logic Seminar for World Logic Day (speaker: Vasco Brattka)

Cross-Alps Logic Seminar

1/9/2023 2:00:00

On Friday 13.01.2023 at 16:00

on the occasion of World Logic Day 2023, a special session of the Cross-Alps Logic Seminars will take place, with special guest

**Vasco Brattka** (Universität der Bundeswehr München)

who will give a talk on

**Some fascinating topics in logic around reducibilities**

Please refer to the usual webpage of our LogicGroup for more details and the abstract of the talk.

The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

## Wednesday seminar

Prague Set Theory Seminar

1/8/2023 13:26:38

Dear all,
The seminar meets on Wednesday January 11th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jaroslav Supina -- Katětov order on ideals and the
Fréchet-Urysohn property
We show that the Katětov order on ideals on natural numbers is a useful
tool in answering a question posed by J. Gerlits and Zs. Nagy and two
questions by M. Sakai. The questions are related to local topological
properties of a space of all continuous functions on an underlying
topological space, the most known among them being the Fréchet-Urysohn
property. This is a joint work with S. Bardyla and L. Zdomskyy.
Best,
David

## (KGRC) seminar talks Tuesday, January 10 and Thursday, January 12

Kurt Godel Research Center

1/5/2023 15:45:05

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31, 2023.
Clifton Ealy (host: Matthias Aschenbrenner) visits the KGRC until August
15.
Tomasz Żuchowski (host: Damian Sobota) visits the KGRC from January 9 to
January 17.
Jerzy Kąkol (host: Damian Sobota) visits the KGRC from February 27 to
March 3.
Manuel López Pellicer (host: Damian Sobota) visits the KGRC from February
27 to March 3.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, January 10
"A weak form of Global Choice under the GCH, part 1"
Peter Holy (TU Wien)
In 2012, Joel Hamkins asked (on MathOverflow) whether it is possible for
the universe of sets to have a linear ordering, but no wellordering (that
is, global choice fails). This question, which I consider very
interesting, appears to still be open. In my talk, I want to present a
somewhat related result. After providing a gentle introduction to second
order set theory and the principle of global choice (no knowledge on these
matters is assumed), we consider a different weakening of global choice
under the GCH: The minimal ordinal-connection axiom MOC due to Rodrigo
Freire. It is equivalent to the statement that the universe of sets can be
stratified by a subset-increasing hierarchy with
each K_alpha of the same size as alpha, and such that K_kappa=H(kappa),
the collection of sets of hereditary size less than kappa, for every
regular infinite cardinal kappa. In this form, it clearly implies the GCH,
and is easily seen to be a weak form of global choice under the GCH. We
will show, using class forcing products of adding Cohen subsets of regular
cardinals (without assuming any particular knowledge regarding the
technique of class forcing), that MOC can consistently fail in models of
the GCH, and that MOC can consistently hold while global choice fails.
This is joint work with Rodrigo Freire (University of Brasilia).
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at Uni
Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, January 12
"Order-preserving Martin's Conjecture"
Benjamin Siskind (Carnegie Mellon University, US)
We'll talk about the current status of Martin's Conjecture, a conjecture
positing that, up to equivalence almost-everywhere, the only natural
functions on the Turing Degrees are the well-known ones: constant
functions, the identity, and transfinite iterates of the Turing Jump.
While the full conjecture is open even for low-level Borel functions, the
order-preserving case seems much more tractable. We'll discuss recent
progress on this order-preserving version of Martin's Conjecture.
This is joint work with Patrick Lutz.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom for both talks: If you need the Zoom data and have not received the
meeting link by the day before the talk, please contact
richard.springer@univie.ac.at! (Please direct any other requests about the
Zoom meeting(s) to vera.fischer@univie.ac.at.)

## Wednesday seminar

Prague Set Theory Seminar

1/2/2023 8:44:03

Dear all,
The seminar meets on Wednesday January 4th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jonathan Cancino Manriquez -- Ideal independent families and
ultrafilters
A family X of infinite subsets of natural numbers is an ideal
independent family if no element of X is almost contained in the union
of finitely many other sets in the family X. The ideal independence
number, s_mm, is defined as the minimal cardinality of an ideal
independent family. These notions were introduced by D. Monk several
years ago, and in joint work with O. Guzmán and A. Miller it was proved
that the dominating number is a lower bound for s_mm, among other
things. In recent work with V. Fischer and C. B. Switzer it was proved
that the ultrafilter number is a lower bound for s_mm, that the spectrum
of ideal independent families can be quite wide and also a preservation
theorem for ideal independent families along countable support
iterations. In this talk we will review some of these results.
Best,
David

## Nankai Logic Colloquium

Nankai Logic Colloquium

12/27/2022 0:57:11

Hello everyone,

Happy Holiday! This is going to be the last event this semester. Our Nankai Logic Colloquium is going to be resumed on Feb.10, 2023.

This week our weekly Nankai Logic Colloquium is going to be in the morning but at a different time.

Our speaker this week will be Liang Yu from Nanjing University. This talk is going to take place this Friday, Dec 30, 2022, from 10 am to 11 am(UTC+8, Beijing time).

Title: Some applications of recursion theory to descriptive set theory.

Abstract: We present some applications of recursion theory to descriptive set theory.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 14th Nankai Logic Colloquium --Liang Yu

Time： 10:00am, Dec. 30, 2022 (Beijing Time)

Zoom Number： 853 2314 4903

Passcode： 153780

Link：https://us02web.zoom.us/j/85323144903?pwd=blBJNTNQbFdGcnc1SngxNE1wVjZidz09

_____________________________________________________________________

Best wishes,

Ming Xiao

## Wednesday seminar

Prague Set Theory Seminar

12/19/2022 9:43:50

Dear all,
The seminar meets on Wednesday December 21st at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
After the seminar the Christmas meeting of employees and friends of the
Institute starts at 16:00 in the blue lecture hall.
Program: David Chodounsky -- Big Ramsey degrees of metric spaces
Hubicka developed a new method for proving finiteness of Big Ramsey
degrees of universal structures via the Carlson–Simpson theorem. Using
this method we derive a new condition for structures in binary languages
which implies finite big Ramsey degrees. In particular, for a given
finite set of distances the countable universal metric space with only
these distances satisfies the condition.
Joint work with Martin Balko, Jan Hubicka, Matej Konecny, Jaroslav
Nesetril, and Lluis Vena
https://arxiv.org/abs/2105.12184
Best,
David

## Nankai Logic Colloquium

Nankai Logic Colloquium

12/18/2022 4:23:19

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Victor Selivanov from the A.P. Ershov Institute of Informatic Systems. This talk is going to take place this Friday, Dec 23, 2022, from 16:00 to 17:00 (UTC+8, Beijing time).

Title: Effective descriptive theory of quasi-Polish spaces

Abstract: Quasi-Polish spaces appeared about ten years ago as a natural extension of Polish spaces which includes many non-Hausdorff spaces of interest to mathematics and computer science (like omega-continuous domains and countably based spectral spaces). In this talk we give a partial survey of results in descriptive set theory of quasi-Polish spaces, including some recent results on effective descriptive set theory and Wadge hierarchy. We will also mention possible new research directions and open questions.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 13th Nankai Logic Colloquium --Victor Selivanov

Time： 16:00pm, Dec. 23, 2022 (Beijing Time)

Zoom Number：843 9471 9093

Passcode： 481891

Link： https://us02web.zoom.us/j/84394719093?pwd=S2VnM21YTWppSm9WYk5UTE5IVmlYdz09

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY - Special announcement: Logic at JMM

This Week in Logic at CUNY

12/13/2022 12:07:11

Hi everyone,

I wanted to pass along the following information on logic events at the Joint Mathematics Meetings in early January.

Best,

Jonas

--------------------------

The Joint Mathematics Meetings will be held in Boston next month (January 4-7, 2023). We’re very pleased that there will be a full slate of logic events, and we thought you might like to see the list.1. Definability, Computability, and Model Theory: A Special Session dedicated to Gerald E. Sackshttps://www.jointmathematicsmeetings.org/meetings/national/jmm2023/2270_program_ss51.htmlThis special session is dedicated both to Prof. Sacks' memory and to his wide mathematical influence. It will include talks in a range of mathematical areas, including computability theory, model theory, and set theory.Session I: Wednesday January 4, 2023, 8:00 a.m.-12:00 p.m.Session II: Wednesday January 4, 2023, 1:00 p.m.-6:00 p.m.Session III: Thursday January 5, 2023, 8:00 a.m.-12:00 p.m.Independence East, Sheraton Boston HotelOrganizers: Nathanael L. Ackerman, Cameron E. Freer, Theodore A. SlamanSpeakers: John T. Baldwin, Lenore Blum, Johanna N. Y. Franklin, Marcia Groszek, Valentina Harizanov, Steve Homer, A. Kanamori, Manuel Lerman, Montgomery Link, Robert S. Lubarsky, Maryanthe Malliaris, Rahim Nazim Moosa, Anil Nerode, Richard A. Shore, Stephen G. Simpson, Carol Saunders Wood----2. ASL Special Session on Model-theoretic and "Higher Infinite" Methods in Descriptive Set Theory and Related Areashttps://www.jointmathematicsmeetings.org/meetings/national/jmm2023/2270_program_aslss1.htmlThursday January 5, 2023, 1:00 p.m.-5:00 p.m.306, Hynes Convention CenterOrganizers: Rehana Patel, Alexander Kechris, Alejandro Poveda, Assaf ShaniSpeakers: Dana Bartosova, Tom Benhamou, Filippo Calderoni, Michael Chris Laskowski, Aristotelis Panagiotopoulos, Forte Shinko, Dima Svetosla Sinapova, Jenna Zomback----3. ASL Special Session on Tame Geometry and Applications to Analysishttps://www.jointmathematicsmeetings.org/meetings/national/jmm2023/2270_program_aslss2.html#titleThursday January 5, 2023, 8:00 a.m.-12:00 p.m.306, Hynes Convention CenterOrganizers: Alexi Block Gorman, Elliot Kaplan, Daniel MillerSpeakers: Chris Miller, Adele Padgett, Nigel Pynn-Coates, Ary Shaviv, Margaret E. M. Thomas, Siegfried Van Hille----4. ASL Tutorial: Hilbert's Tenth Problem: Between logic and number theoryhttps://meetings.ams.org/math/jmm2023/meetingapp.cgi/Program/1081Session I: Wednesday January 4, 2023, 9:00 a.m.-10:00 a.m.Session II: Wednesday January 4, 2023, 1:00 p.m.-2:00 p.m.306, Hynes Convention CenterSpeaker: Sylvy Anscombe----5. ASL Invited Talkshttps://aslonline.org/wp-content/uploads/2022/10/2023JMM_Long_Program.pdfhttps://aslonline.org/wp-content/uploads/2022/10/2023JMM_ShortProgram.pdfFriday January 6 and Saturday January 7, 2023306, Hynes Convention CenterProgram Committee: Dana Bartošová, Kirsten Eisenträger, James Freitag (chair) and Philipp HieronymiSpeakers: Jeremy David Avigad, Peter Cholak, Franziska Jahnke, Sandra Müller, Lynn Scow, Assaf Shani, Erik Donal Walsberg----6. ASL Contributed Paper Sessionhttps://www.jointmathematicsmeetings.org/meetings/national/jmm2023/2270_program_friday.html#2270:ASLCP1AFriday January 6, 2023, 3:00 p.m.-6:00 p.m.306, Hynes Convention CenterOrganizer: David Reed SolomonSpeakers: Athar Abdul-Quader, Jananan Arulseelan, Katalin Bimbo, Daniel Mourad, Carl Mummert, Dan Turetsky
## Wednesday seminar

Prague Set Theory Seminar

12/12/2022 2:51:22

Dear all,
The seminar meets on Wednesday December 14th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
There is no fixed program yet. Walk-in speakers will be welcomed.
Best,
David

## Nankai Logic Colloquium

Nankai Logic Colloquium

12/12/2022 1:32:54

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Luca Motto Ros from the University of Turin. This talk is going to take place this Friday, Dec.16.2022, from 16:00 to 17:00 (UTC+8, Beijing time).

Title

Universality properties of graph homomorphism: one construction to prove them all

Abstract

We show that the natural operation of connected sum for graphs can be used to prove at once most of the universality results from the literature concerning graph homomorphism. In doing so, we significantly improve many existing theorems and we also solve some natural open problems. Despite its simplicity, our technique unexpectedly leads to applications in quite diverse areas of mathematics, such as category theory, combinatorics, classical descriptive set theory, generalized descriptive set theory, model theory, and theoretical computer science.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 12th Nankai Logic Colloquium -- Luca Motto Ros

Time： 16:00pm, Dec. 16, 2022 (Beijing Time)

Zoom Number：880 9576 5955

Passcode： 289312

Link： https://us02web.zoom.us/j/88095765955?pwd=b0FiczEwQURVWkpKRjlFZndpNmtwQT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

12/11/2022 22:30:00

Hi everyone,

This Wednesday's talk in the The New York City Category Theory Seminar has been postponed until Spring. As final exams begin this week at CUNY, I believe there are no further talks scheduled until after the New Year. This Week in Logic will resume regular mailings at the end of January 2023.

Happy Holidays to all!

Jonas

This Week in Logic at CUNY:

- - - - Monday, Dec 12, 2022 - - - -- - - - Tuesday, Dec 13, 2022 - - - -- - - - Wednesday, Dec 14, 2022 - - - -

- - - - Thursday, Dec 15, 2022 - - - -- - - - Friday, Dec 16, 2022 - - - -

Next Week in Logic at CUNY:

- - - - Monday, Dec 19, 2022 - - - -

- - - - Tuesday, Dec 20, 2022 - - - -

- - - - Wednesday, Dec 21, 2022 - - - -

- - - - Thursday, Dec 22, 2022 - - - -

- - - - Friday, Dec 23, 2022 - - - -

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## (KGRC) CORRECTED: seminar talks Tuesday, December 13 and Thursday, December 15

Kurt Godel Research Center

12/8/2022 17:06:02

(Note: In a version of these announcements sent out earlier today I failed to
mention Ralf Schindler's talk. The text below corrects for this.)
* * *
The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31, 2023.
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC until December 14.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, December 13
"The weak Ramsey property"
Wiesław Kubiś
(Czech Academy of Sciences, CZ)
The weak Ramsey property is a variant of the finite Ramsey property, used
for characterizing extreme amenability of automorphism groups of
ultra-homogeneous structures, known as the Kechris - Pestov - Todorcevic
correspondence. We shall describe a far reaching extension of the KPT
correspondence, indicating also how it works in metric-enriched
categories, capturing objects from topology and functional analysis.
Joint work with A. Bartos, T. Bice, and K. Dasilva Barbosa.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, December 15
"Abstract Evolution Systems"
Wiesław Kubiś
(Czech Academy of Sciences, CZ)
An abstract evolution system is a category endowed with a fixed family of
arrows (called transitions) and with a distinguished object, called the
origin. An evolution is an infinite sequence of transitions starting from
the origin. We will show that evolution systems provide a good framework
for the study of highly symmetric mathematical structures, namely those
having rich automorphism groups. On the other hand, evolution systems also
describe terminating transition systems, leading to an extension of the
celebrated Newman's Lemma: A locally confluent terminating system is
confluent.
(Joint work with P. Radecka)
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, December 15
"Martin's Maximum, Woodin's P_max axiom (*), and Cantor's Continuum Problem"
Ralf Schindler (U Münster, DE)
In 2019, D. Asperó and the speaker showed that Martin's Maximum^++ implies
the P_max axiom (*). This amalgamated two prominent maximality principles
which before had often been considered as competitors. We provide some
background and give an outline of the proof method. We also discuss to
which extent our result has an impact on the question as to how many real
numbers there are.
Time and Place
Talk at 4:45pm in hybrid mode, in person as well as via Zoom.
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
ground floor
room HS 2
Zoom for all three talks: If you need the Zoom data and have not received
the meeting link by the day before the talk, please contact
richard.springer@univie.ac.at! (Please direct any other requests about the
Zoom meeting(s) to vera.fischer@univie.ac.at.)

## This Week in Logic at CUNY

This Week in Logic at CUNY

12/4/2022 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Dec 5, 2022 - - - -

Rutgers Logic Seminar

Monday, December 5, 3:30pm, Rutgers University, Hill 705

Takehiko Gappo, Rutgers

Determinacy in the Chang model from a hod pair

Logic and Metaphysics WorkshopDate: Monday, November 28, 4.15-6.15 (NY time), GC 7314For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/Martin Pleitz (Muenster)

Title: Reification as identity?

Abstract: Abstract objects like properties and propositions, I believe, are the result of reification, which can intuitively be characterized as the metaphysical counterpart of nominalization (as in the shift, e.g., from ‘is a horse’ to ‘the property of being a horse’; cf. Schiffer, Moltmann), and occurs paradigmatically in the well-known bridge laws for instantiation, truth, etc. (e.g., something instantiates the property of being a horse iff it is a horse). So far, I have been working on an account of reification in terms of the technical notions of encoding & decoding, as some regulars at the L+M workshop may recall. In my upcoming talk, I wish to embed reification more clearly in higher-order metaphysics and explore an alternative idea: Can reification be construed as identification across metaphysical categories? E.g., can the object that is the property of being a horse be identified, in some sense, with Frege’s concept horse, which is a non-objectual item because ‘is a horse’ is not a singular term? In my presentation I will argue for an affirmative answer. For this, I will sketch an ultra-generalized logic of equivalence, which has as its special cases (i) the well-known logics of first-order identity and equivalence, (ii) recent logics of generalized identities (à la Rayo, Linnebo, Dorr, Fine, Correia, Skiles, …) which connect higher-order items of the same type, and (iii) the logic of my proposed cross-level equivalences which connect items of different types. In a second step, I will re-construe reification as the cross-level equivalence that holds between higher-order items and abstract objects of the appropriate sort and argue that this account of reification as identity has certain advantages.

- - - - Tuesday, Dec 6, 2022 - - - -

- - - - Wednesday, Dec 7, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: ** Robert Pare, Dalhousie University.**

Date and Time: ** Wednesday December 7, 2022, 7:00 - 8:30 PM.**

Title:** The horizontal/vertical synergy of double categories.**

Abstract: A double category is a category with two types of arrows, horizontal and vertical, related by double cells. Think of sets with functions and relations as arrows and implications as double cells. The theory is 2-dimensional just like for 2-categories. In fact 2-categories were originally defined as double categories in which all vertical arrows were identities. Most of the theory of 2-categories extends to double categories resulting in a deeper understanding. This is one aspect of double categories: they’re “new and improved” 2-categories.

From a purely formal point of view, a double category is a category object in CAT. Once a familiarity with double categories has developed, it is amusing and instructive to see how the various constructs of formal category theory play out in this setting.

But these two aspects of double categories, fancy 2-categories or internal categories, are only part of the picture. Perhaps the most important thing is the interplay between the horizontal and the vertical.

I will start with some examples of double categories to give a feeling for the objects I will be discussing, and then look at several concepts indicative of the rich interplay between the horizontal and the vertical.

- - - - Thursday, Dec 8, 2022 - - - -

- - - - Friday, Dec 9, 2022 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, December 9, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id. Vladimir Kanovei Institute for Information Transmission Problems

**On the significance of parameters in the comprehension and choice schemata in second-order arithmetic**

Parameters are free variables in various axiom schemata in PA, ZFC, and other similar theories. Given an axiom schema S, we let S* be the parameter-free sub-schema.

Kreisel (A survey of proof theory, JSL 1968) was one of those who paid attention to the comparison of some schemata in second-order PA and their parameter-free versions. In particular, Kreisel noted that

[...] if one is convinced of the significance of something like a given axiom schema, it is natural to study details, such as the effect of parameters.

This talk is devoted to the effect of parameters in the schemata of Comprehension and Choice in second-order arithmetic.

Logic WorkshopCUNY Graduate CenterHybrid: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.Friday December 9, 2:00pm-3:30pm, Room 6417 Daniel Turetsky, Victoria University of Wellington

Wadge degrees, games, and the separation and reduction properties

In this talk, I will give an overview of the picture of the Borel Wadge degrees. Our system of descriptions allows us to describe their Delta-classes, as well as specify which degrees have the separation or reduction properties. Part of our analysis is based on playing games along our descriptions, and so I will explain how these games are played and what they can tell us.

Next Week in Logic at CUNY:- - - - Monday, Dec 12, 2022 - - - -- - - - Tuesday, Dec 13, 2022 - - - -- - - - Wednesday, Dec 14, 2022 - - - -The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: Gemma De las Cuevas, University of Innsbruck.

Date and Time: Wednesday December 14, 2022, 7:00 - 8:30 PM.

Title: A framework for universality across disciplines.

Abstract: What is the scope of universality across disciplines? And what is its relation to undecidability? To address these questions, we build a categorical framework for universality. Its instances include Turing machines, spin models, and others. We introduce a hierarchy of universality and argue that it distinguishes universal Turing machines as a non-trivial form of universality. We also outline the relation to undecidability by drawing a connection to Lawvere’s Fixed Point Theorem. Joint work with Sebastian Stengele, Tobias Reinhart and Tomas Gonda.

- - - - Thursday, Dec 15, 2022 - - - -- - - - Friday, Dec 16, 2022 - - - -

- - - - Other Logic News - - - -Post doc in logic/metaphysics:

**JOB: 6-Month Visiting Fellowship at the Complutense University of Madrid**

The Project “Unstable Metaphysics” led by Elia Zardini and Sergi Oms at the Department of Logic and Theoretical Philosophy of the Complutense University of Madrid is pleased to offer a Postdoctoral Visiting Fellowship for six months starting in early 2023 (the exact start is somewhat flexible). The fellow will work on applications of nonclassical logics to metaphysics. The exact amount of the net salary will depend on the circumstances of the successful applicant, but can be expected to be around 1,400 EUR per month.

To be considered, applicants should submit their (1) CV, (2) PhD certificate (or declaration concerning submission of PhD thesis) and (3) a short (max 1,000 words) research proposal on the above-mentioned topic to

ezardini@ucm.es no later than December 11th 2022 (informal inquiries can be directed to the same email address).

- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.

## Wednesday seminar

Prague Set Theory Seminar

12/4/2022 10:17:10

Dear all,
The seminar does not meet next week, Wednesday December 7th.
(Some regular seminar participants are away.)
The seminar should meet again on Wednesday December 14th.
Best,
David

## Upcoming core model seminar

Carnegie Mellon Logic Seminar

12/2/2022 12:43:55

TUESDAY, December 6, 2022
Core Model Seminar: 1:30 - 3 PM Eastern, Online, Gabriel Goldberg,
University of California, Berkeley
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: External ultrapowers of HOD in models of determinacy
ABSTRACT: We show that in L(R) under determinacy, the external ultrapower
of HOD^L(R) by a countably complete ultrafilter on an ordinal less than
theta^L(R) is a normal iterate of HOD^L(R) via its iteration strategy.
This is joint work with Grigor Sargsyan.
ORGANIZERS' NOTE: This is the final meeting of 2022 after which the
seminar will resume on January 24, 2023.

## (KGRC) two talks in the Set Theory Seminar on Tuesday, December 6

Kurt Godel Research Center

12/1/2022 11:59:22

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31, 2023.
David Chodounsky (host: Vera Fischer) visits the KGRC from December 4
until December 8 and gives a talk on December 6 (see below).
Jan Hubicka (host: Vera Fischer) visits the KGRC from December 5 until
December 8 and gives a talk on December 6 (see below).
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC from December 5 to December 14.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, December 6
"Introduction to big Ramsey degrees"
David Chodounský
(Czech Academy of Sciences, CZ)
I will give a quick introduction to big Ramsey degrees, sketch proofs of
some basic results, and I will try to explain the ideas behind these
proofs.
The talk is intended as an introduction to the topic, setting up the
background for the talk of Jan Hubička. There will be a substantial
overlap with the talk I gave at this seminar in June 2021.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, December 6
(Please note the unusual time and place!)
"Big Ramsey degrees for structures with forbidden substructures"
Jan Hubička
(Charles University, CZ)
We discuss a new method used to prove that big Ramsey degrees of a given
structure are finite. We start with a simple new proof of the theorem by
Dobrinen showing the big Ramsey degrees of the homogeneous triangle free
graphs are finite. This is based on an application of the Carlson-Simpson
theorem. We outline how this proof can be carried to other structures
including partial orders and metric spaces. Then we discuss a new theorem
for trees with a successor operation that can be used to give bounds on
big Ramsey degrees for structures with bigger forbidden configurations and
in languages with higher arity.
Time and Place
Talk at 4:45pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 9
Zoom for both talks: If you need the Zoom data and have not received the
meeting link by the day before the talk, please contact
richard.springer@univie.ac.at! (Please direct any other requests about the
seminar and Zoom meeting(s) to vera.fischer@univie.ac.at.)

## (KGRC) talks Tuesday, November 29 and Wednesday, November 30

Kurt Godel Research Center

11/28/2022 11:05:05

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31, 2023.
David Chodounsky (host: Vera Fischer) visits the KGRC from December 4
until December 8 and gives a talk on December 6 (details to be announced
at a later time).
Jan Hubicka (host: Vera Fischer) visits the KGRC from December 5 until
December 8 and gives a talk on December 6 (details to be announced at a
later time).
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC from December 5 to December 14.
* * *
FG1 Seminar
Institute of Discrete Mathematics and Geometry, TU Wien
Tuesday, November 29
"Large cardinals and properties of generalized logics"
Menachem Magidor
(Hebrew University of Jerusalem, IL)
This is a joint work with Will Boney, Stamis Dimipoulos and Victoria
Gitman.
It is well known that many large cardinals properties and schemata can be
phrased as regularities properties of generalized logics. (Typical
examples are Skolem-Löwenheim and compactness properties.) In this talk we
shall present some additional such characterizations.
An example is the connection between subtle cardinals and the existence of
weak compactness for every abstract logic or the characterization of
various virtual cardinals in terms of variations of compactness properties
appropriate for the context of virtual large cardinals.
Time and Place
Talk at 9:00am
TU Wien
Institut für Diskrete Mathematik und Geometrie
Wiedner Hauptstrasse 8-10
Turm A (green)
8th floor
Dissertantenraum
Please direct any questions about this talk to algebra@dmg.tuwien.ac.at.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, November 29
"Subversion Forcing"
Corey Switzer (KGRC)
In these two talks we will introduce Jensen's classes of subcomplete and
subproper forcing as well as discuss some applications due to the speaker
and Fuchs, and the speaker and Sakai. An important feature of proper
forcing is the countable covering property: every countable set of
ordinals added by a proper forcing notion is contained in a ground model
countable set of ordinals. This is important in iteration theorems.
Subproper forcing is a weakening of proper forcing that is still iterable
while including some well known forcing notions which do add countable
sets of ordinals that are not covered by anything in the ground model
including Namba forcing (under CH) and Prikry forcing. One can weaken
other classes of forcing notions in a similar way and the "sub"version of
the countably closed forcing, known as subcomplete forcing, is a
particularly interesting subclass of subproper forcing that was used by
Jensen in several applications including his solution to the extended
Namba problem.
In the first of these talks I will introduce the classes subproper and
subcomplete forcing as well as discuss simplifications of them due to
Fuchs and myself. Time permitting I will discuss new iterations theorems
for these classes reminiscent of similar theorems proved for proper
forcing in the context of the reals and combinatorics on $\omega_1$
($\omega^\omega$-bounding, preservation of Souslin trees etc). In the
second talk I will discuss the forcing axioms for these classes including
their applications and limitations. In particular, time permitting, I will
discuss a recent result, joint with Hiroshi Sakai that the forcing axiom
for subcomplete forcing is compatible with a
$\square_{\omega_1}$-sequence. The take away is a class of strong forcing
axioms that are compatible with a wide variety of behaviour on the level
of the reals and combinatorics on cardinals below the continuum.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom: If you need the Zoom data and have not received the meeting link by
the day before the talk, please contact richard.springer@univie.ac.at!
(Please direct any other requests about this talk to
vera.fischer@univie.ac.at.)
* * *
Mathematisches Kolloquium
Faculty of Mathematics
Wednesday, November 30
"Regularity properties of subsets of the real line and other polish spaces"
Menachem Magidor
(Hebrew University of Jerusalem, IL)
Using the axiom of choice one can construct set of reals which are
pathological in some sense. Similar constructions can produce such
"pathological" subsets of any non-trivial Polish space (= a complete
separable metric space). Typical examples of "pathology" is the set being
non-measurable, lacking the property of Baire (= not equivalent to an open
set modulo meager set), being a counter example to generalizations of
Ramsey theorem.
A subset of the Baire space N^N is "pathological" if in the associated
game, no player has a winning strategy. A prevailing paradigm in
Descriptive Set Theory is that sets that has a "simple description" should
not be pathological. Evidence for this maxim is the fact that Borel sets
are not pathological in any of the senses described above. In this talk we
shall present a notion of "super regularity" for subsets of a Polish
space, the family of universally Baire sets.
The universally Baire sets typically do not show the "pathologies" we
listed above, especially if one assumes the existence of large cardinals.
We shall try to describe the deep impact that the existence of the large
cardinals has on the structure of definable sets of reals and universally
Baire sets.
The talk should be accessible to a wide mathematical audience.
Time and Place
Coffee at 3:45pm
Talk at 4:15pm
Faculty of Mathematics
Oskar-Morgenstern-Platz 1
1090 Vienna
12th floor
Sky Lounge
Please direct any questions about this talk to vera.fischer@univie.ac.at.

## Wednesday seminar

Prague Set Theory Seminar

11/28/2022 8:19:45

Dear all,
The seminar meets on Wednesday November 30th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
There is no fixed program yet. Walk-in speakers will be welcomed.
Best,
David

## Cross-Alps Logic Seminar (speaker: Francesco Parente)

Cross-Alps Logic Seminar

11/28/2022 3:29:09

On Friday 2.12.2022 at 16:00

**Francesco Parente** (University of Turin)

will give a talk on

*Good ultrafilters and universality properties of forcing*Please refer to the usual webpage of our

LogicGroup for more details and the abstract of the talk.

The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

## Nankai Logic Colloquium

Nankai Logic Colloquium

11/28/2022 1:47:42

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Todor Tsankov from Université Lyon 1. This talk is going to take place this Friday, Dec.02.2022, from 4 pm to 5 pm (UTC+8, Beijing time).

Title: Extremal models in affine logic
Abstract: Affine logic is a fragment of continuous logic, introduced by Bagheri,
where one allows only affine functions R^n -> R as connectives instead
of arbitrary continuous functions. This decreases the expressive power
of the logic and provides additional structure on the type spaces:
namely, the structure of compact, convex sets. An important role in
convex analysis is played by the extreme points of these sets and,
unsurprisingly, extremal models, in which only extreme types are
realized, are crucial for developing affine model theory.
In a joint work with Itaï Ben Yaacov and Tomás Ibarlucía, we develop
the basic theory of extremal models. Some highlights include a general
integral decomposition theorem (generalizing the ergodic decomposition
theorem from ergodic theory) and affine aleph_0-categoricity:
theories admitting a unique separable, extremal model.
In the talk, I will give a gentle introduction to affine logic and will
explain some of our main results.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 11th Nankai Logic Colloquium -- Todor Tsankov

Time： 16:00pm, Dec. 2, 2022 (Beijing Time)

Zoom Number：817 7281 1616

Passcode： 468722

Link： https://us02web.zoom.us/j/81772811616?pwd=ZGU2UHlSbEYzL3lQOUk0YzFPeTRLUT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

11/27/2022 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Nov 28, 2022 - - - -

Logic and Metaphysics WorkshopDate: Monday, November 28, 4.15-6.15 (NY time), GC 7314For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/William McCarthy (Columbia).

Title: Modal pluralism and higher-order logic

Abstract: Modal pluralism is the view that there are a variety of candidate interpretations of the predicate ‘could have been the case that’ which give intuitively different answers to paradigmatic metaphysical questions (‘intuitively’ because the phrase means subtly different things on the different interpretations). It is the modal analog of set-theoretic pluralism, according to which there are a variety of candidate interpretations of ‘is a member of’. Of course, if there were a broadest kind of counterfactual possibility, then one could define every other kind as a restriction on it, as in the set-theoretic case. It would then be privileged in the way that a broadest kind of set would be, if there were one. Recently, several authors have purported to prove from higher-order logical principles that there is a broadest kind of possibility. In this talk we critically assess these arguments. We argue that they rest on an assumption which any modal pluralist should reject: namely, monism about higher-order logic. The reasons to be a modal pluralist are also reasons to be a pluralist about higher-order quantification. But from the pluralist perspective on higher-order logic, the claim that there is a broadest kind of possibility is like the Continuum Hypothesis, according to the set-theoretic pluralist. It is true on some interpretations of the relevant terminology, and false on others. Consequently, the significance of the ‘proof’ that there is a broadest kind of possibility is deflated. Time permitting, we will conclude with some upshots of higher-order pluralism for the methodology of metaphysics.

Note: This is joint work with Justin Clarke-Doane.

- - - - Tuesday, Nov 29, 2022 - - - -

- - - - Wednesday, Nov 30, 2022 - - - -

- - - - Thursday, Dec 1, 2022 - - - -

- - - - Friday, Dec 2, 2022 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, December 2, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id. Will Boney Texas State University

Logic WorkshopCUNY Graduate CenterHybrid: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.Friday December 2, 2:00pm-3:30pm, Room 6417 Michał Tomasz Godziszewski University of Vienna

Next Week in Logic at CUNY:

- - - - Monday, Dec 5, 2022 - - - -

Rutgers Logic Seminar

Monday, December 5, 3:30pm, Rutgers University, Hill 705

Takehiko Gappo, Rutgers

Determinacy in the Chang model from a hod pair

Logic and Metaphysics WorkshopDate: Monday, November 28, 4.15-6.15 (NY time), GC 7314For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/Martin Pleitz (Muenster)

Title: Reification as identity?

Abstract: Abstract objects like properties and propositions, I believe, are the result of reification, which can intuitively be characterized as the metaphysical counterpart of nominalization (as in the shift, e.g., from ‘is a horse’ to ‘the property of being a horse’; cf. Schiffer, Moltmann), and occurs paradigmatically in the well-known bridge laws for instantiation, truth, etc. (e.g., something instantiates the property of being a horse iff it is a horse). So far, I have been working on an account of reification in terms of the technical notions of encoding & decoding, as some regulars at the L+M workshop may recall. In my upcoming talk, I wish to embed reification more clearly in higher-order metaphysics and explore an alternative idea: Can reification be construed as identification across metaphysical categories? E.g., can the object that is the property of being a horse be identified, in some sense, with Frege’s concept horse, which is a non-objectual item because ‘is a horse’ is not a singular term? In my presentation I will argue for an affirmative answer. For this, I will sketch an ultra-generalized logic of equivalence, which has as its special cases (i) the well-known logics of first-order identity and equivalence, (ii) recent logics of generalized identities (à la Rayo, Linnebo, Dorr, Fine, Correia, Skiles, …) which connect higher-order items of the same type, and (iii) the logic of my proposed cross-level equivalences which connect items of different types. In a second step, I will re-construe reification as the cross-level equivalence that holds between higher-order items and abstract objects of the appropriate sort and argue that this account of reification as identity has certain advantages.

- - - - Tuesday, Dec 6, 2022 - - - -

- - - - Wednesday, Dec 7, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: ** Robert Pare, Dalhousie University.**

Date and Time: ** Wednesday December 7, 2022, 7:00 - 8:30 PM.**

Title:** The horizontal/vertical synergy of double categories.**

Abstract: A double category is a category with two types of arrows, horizontal and vertical, related by double cells. Think of sets with functions and relations as arrows and implications as double cells. The theory is 2-dimensional just like for 2-categories. In fact 2-categories were originally defined as double categories in which all vertical arrows were identities. Most of the theory of 2-categories extends to double categories resulting in a deeper understanding. This is one aspect of double categories: they’re “new and improved” 2-categories.

From a purely formal point of view, a double category is a category object in CAT. Once a familiarity with double categories has developed, it is amusing and instructive to see how the various constructs of formal category theory play out in this setting.

But these two aspects of double categories, fancy 2-categories or internal categories, are only part of the picture. Perhaps the most important thing is the interplay between the horizontal and the vertical.

I will start with some examples of double categories to give a feeling for the objects I will be discussing, and then look at several concepts indicative of the rich interplay between the horizontal and the vertical.

- - - - Thursday, Dec 8, 2022 - - - -

- - - - Friday, Dec 9, 2022 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, December 9, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id. Vladimir Kanovei Institute for Information Transmission Problems

Logic WorkshopCUNY Graduate CenterHybrid: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.Friday December 9, 2:00pm-3:30pm, Room 6417 Daniel Turetsky, Victoria University of Wellington

Wadge degrees, games, and the separation and reduction properties

In this talk, I will give an overview of the picture of the Borel Wadge degrees. Our system of descriptions allows us to describe their Delta-classes, as well as specify which degrees have the separation or reduction properties. Part of our analysis is based on playing games along our descriptions, and so I will explain how these games are played and what they can tell us.

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Core model seminar on Tuesday

Carnegie Mellon Logic Seminar

11/25/2022 11:42:39

TUESDAY, November 29, 2022
Core Model Seminar: 1:30 - 3 PM Eastern, Online, Benjamin Siskind,
Carnegie Mellon University
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: Full normalization and HOD^L(R)
ABSTRACT: We'll review some aspects of the HOD analysis of L(R) and
introduce the full normalization machinery developed by Steel and
Schlutzenberg. We'll use this to show that HOD^L(R)|theta is actually a
normal iterate of M_omega|delta via M_omega's canonical iteration strategy
(and a bit more), a result of Steel and Schlutzenberg. Time permitting, we
may discuss other applications of full normalization, due to Steel.

## Nankai Logic Colloquium

Nankai Logic Colloquium

11/21/2022 6:08:06

Hello everyone,

There is no NLC this week. Instead...the Chinese Annual Conference on Mathematical Logic (CACML 2022) will be held from Nov. 25 to Nov. 27 (UTC+5, Beijing Time)!

This conference is hosted by the Mathematical Logic Professional Committee of the Chinese Mathematical Society and organized by the Anhui Polytechnic University. The purpose of the conference is to provide a platform for scholars of mathematical logic and its applications to report the latest achievements, and carry out extensive academic exchanges and cooperation, so as to promote the development of mathematical logic in China.

This conference plans to set up (but not limited to) the following topics: (1) set theory, (2) recursion theory, (3) model theory, (4) philosophy of mathematics. The conference will invite domestic and foreign experts in the field of mathematical logic to make thematic reports on the above topics.

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

11/20/2022 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Nov 21, 2022 - - - -

Logic and Metaphysics WorkshopDate: Monday, November 21, 4.15-6.15 (NY time), GC 7314For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/Marko Malink (NYU) and Anubav Vasudevan (University of Chicago).

Title: The origins of conditional logic: Theophrastus on hypothetical syllogisms

Abstract: Łukasiewicz maintained that “the first system of propositional logic was invented about half a century after Aristotle: it was the logic of the Stoics”. In this talk, we argue that the first system of propositional logic was, in fact, developed by Aristotle’s pupil Theophrastus. Theophrastus sought to establish the priority of categorical over propositional logic by reducing various modes of propositional reasoning to categorical form. To this end, he interpreted the conditional “If φ then ψ” as a categorical proposition “A holds of all B”, in which B corresponds to the antecedent φ, and A to the consequent ψ. Under this interpretation, Aristotle’s law of subalternation (A holds of all B, therefore A holds of some B) corresponds to a version of Boethius’ Thesis (If φ then ψ, therefore not: If φ then not-ψ). Jonathan Barnes has argued that this consequence renders Theophrastus’ program of reducing propositional to categorical logic inconsistent. In this paper, we show that Barnes’s objection is inconclusive. We argue that the system developed by Theophrastus is both non-trivial and consistent, and that the propositional logic generated by Theophrastus’ system is exactly the connexive variant of the first-degree fragment of intensional linear logic.

Rutgers Logic Seminar

Monday, November 21, 5pm, Rutgers University, Hill 705

This specially scheduled seminar will be held at 5pm in order not to clash with the Wales vs USA World Cup match.

Simon Thomas, Rutgers

Invariant Random Subgroups and Characters

- - - - Tuesday, Nov 22, 2022 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, November 22, 1:00pmVirtual (email Victoria Gitman vgitman@nylogic.org for meeting id) **Joel David Hamkins**, University of Notre Dame

**Pointwise definable and Leibnizian extensions of models of arithmetic and set theory**

I shall introduce a flexible new method showing that every countable model of PA admits a pointwise definable end-extension, one in which every individual is definable without parameters. And similarly for models of set theory, in which one may also achieve the Barwise extension result—every countable model of ZF admits a pointwise definable end-extension to a model of ZFC+V=L, or indeed any theory arising in a suitable inner model. A generalization of the method shows that every model of arithmetic of size at most continuum admits a Leibnizian extension, and similarly in set theory.

**Computational Logic Seminar **

**Fall Semester 2022**

**Tuesday, November 22 **

Time 2:00 - 4:00 PM

**Room 3310-B, **

**The talk will be delivered online for a live audience,**

**Speaker**: *Neil De Boer, The Ohio State University *

**Title:** *Justification Logic and Type Theory as Formalizations of Intuitionistic Propositional Logic*

**Abstract:**

We explore two ways of formalizing Kreisel's addendum to the Brouwer-Heyting-Kolmogorov interpretation. To do this we compare Artemov's justification logic with simply typed $\lambda$ calculus. First, we provide a completeness result for Kripke-style semantics of the implicational fragment of the intuitionistic logic of proofs. Then we introduce a map from justification terms into $\lambda$ terms, which can be viewed as a method of extracting the computational content of the justification terms. Then we examine the interpretation of Kreisel's addendum in justification logic along with the image of the resulting justification terms under our map.

- - - - Wednesday, Nov 23, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Speaker: ** Saeed Salehi, University of Tabriz.**

Date and Time: ** Wednesday November 23, 2022, ****Zoom Talk SPECIAL TIME 9:30AM-11:00AM.**

Title:** Self-Reference and Diagonalization: their difference and a short history.**

Abstract: What is now called the Diagonal (or the Self-Reference) Lemma, is the statement that for every formula *F*(*x*), with the only free variable *x*, there exists a sentence *σ* such that *σ* is equivalent to the *F* of the Gödel code of *σ*, i.e., *σ* **≡** *F*(**#***σ*); and this equivalence is provable in certain weak arithmetics. This lemma is credited to Gödel (1931), in the special case when *F* is the *un*provability predicate, and to Carnap (1934) in the more general case.

In this talk, we will argue that Gödel-Carnap's original Diagonal Lemma is not the modern formulation and was more similar to, but not exactly identical with, the Strong Diagonal (or Direct Self-Reference) Lemma. This lemma, so-called recently, says that for every formula *F*(*x*), in a sufficiently expressive language, there exists a sentence *σ* such that *σ* is equal to the *F* of the Gödel code of *σ*, i.e., *σ* **=** *F*(**#***σ*); and this equality is provable in sufficiently strong theories. We will attempt at tracking down the first appearance of the modern formulation of the Diagonal Lemma in the equivalent form, also in the strong direct form of equality.

- - - - Thursday, Nov 24, 2022 - - - -

*** Thanksgiving Day ***

- - - - Friday, Nov 25, 2022 - - - -

Next Week in Logic at CUNY:

- - - - Monday, Nov 28, 2022 - - - -

Logic and Metaphysics WorkshopDate: Monday, November 28, 4.15-6.15 (NY time), GC 7314For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/William McCarthy (Columbia).

Title: Modal pluralism and higher-order logic

Abstract: Modal pluralism is the view that there are a variety of candidate interpretations of the predicate ‘could have been the case that’ which give intuitively different answers to paradigmatic metaphysical questions (‘intuitively’ because the phrase means subtly different things on the different interpretations). It is the modal analog of set-theoretic pluralism, according to which there are a variety of candidate interpretations of ‘is a member of’. Of course, if there were a broadest kind of counterfactual possibility, then one could define every other kind as a restriction on it, as in the set-theoretic case. It would then be privileged in the way that a broadest kind of set would be, if there were one. Recently, several authors have purported to prove from higher-order logical principles that there is a broadest kind of possibility. In this talk we critically assess these arguments. We argue that they rest on an assumption which any modal pluralist should reject: namely, monism about higher-order logic. The reasons to be a modal pluralist are also reasons to be a pluralist about higher-order quantification. But from the pluralist perspective on higher-order logic, the claim that there is a broadest kind of possibility is like the Continuum Hypothesis, according to the set-theoretic pluralist. It is true on some interpretations of the relevant terminology, and false on others. Consequently, the significance of the ‘proof’ that there is a broadest kind of possibility is deflated. Time permitting, we will conclude with some upshots of higher-order pluralism for the methodology of metaphysics.

Note: This is joint work with Justin Clarke-Doane.

- - - - Tuesday, Nov 29, 2022 - - - -

- - - - Wednesday, Nov 30, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

Date and Time: Wednesday November 30, 2022, 7:00 - 8:30 PM.

TBA

- - - - Thursday, Dec 1, 2022 - - - -

- - - - Friday, Dec 2, 2022 - - - -

Set Theory SeminarCUNY Graduate Center, Friday, December 2, 12:15pm NY timeVirtual: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id. Michał Tomasz Godziszewski University of Vienna

Logic WorkshopCUNY Graduate CenterHybrid: Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.Friday December 2, 2:00pm-3:30pm, Room 6417 Will Boney Texas State University

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

11/20/2022 11:50:35

Dear all,
The seminar meets on Wednesday November 23th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Sarka Stejskalova -- Automorphisms of trees
In the talk we will focus on omega_1-trees. We will discuss the number
of nontrivial automorphisms which can exist on a given omega_1-tree. We
will also discuss how to add an automorphism to an omega_1-tree with a
well-behaved forcing, and we will identify some restrictions for these
forcings (for instance, they cannot be sigma-closed for Suslin trees).
In the last part of the talk, we will mention some open questions
regarding automorphisms of omega_1-trees.
Best,
David

## (KGRC) guests, video recordings, seminar talks Tuesday, November 22 and Thursday, November 24

Kurt Godel Research Center

11/18/2022 9:45:34

Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC until
January 31, 2023 and gives a talk on November 24 (see below).
David Chodounsky (host: Vera Fischer) visits the KGRC from December 4
until December 8 and gives a talk on December 6 (details to be announced
at a later time).
Jan Hubicka (host: Vera Fischer) visits the KGRC from December 5 until
December 8 and gives a talk on December 6 (details to be announced at a
later time).
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC from December 5 to December 14.
* * *
For some recent seminar talks, video recordings are available:
"Entire functions and the continuum" by Jonathan Schilhan on November 10:
https://univienna.zoom.us/rec/share/WLqHDNlpF4W__jPMOIXe-OvnibgGCCP3ukttxkfh4MIIHoCUC0q6A69vI_ch6jwY.HImCMpOEXxs60rf3
(passcode t0z4?muN)
"Compactness versus hugeness at successor cardinals, part 2" by Monroe
Eskew on November 15:
https://univienna.zoom.us/rec/share/ciurhrPPdzEQHrCS6ro11bEZ4LPuhKJ5bNGzIcBgSqCsr_NrIGHp2-8U_RiJHIsK.bj-YKnjNACDK1Q4e
(passcode f9xDpS&&)
"The Axiom of Choice and large cardinals" by Farmer Schlutzenberg on
November 17:
https://univienna.zoom.us/rec/share/zlY9CldOLrKfL7R1rIZTZ21MW8YLrk0mRRvXykIWPLU0fpkdPxmguYX7cjH2RCqJ.17d3feAKcAZWTTWu
(passcode wR^81nq7)
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, November 22
"Subversion Forcing, part 1"
Corey Switzer (KGRC)
In these two talks we will introduce Jensen's classes of subcomplete and
subproper forcing as well as discuss some applications due to the speaker
and Fuchs, and the speaker and Sakai. An important feature of proper
forcing is the countable covering property: every countable set of
ordinals added by a proper forcing notion is contained in a ground model
countable set of ordinals. This is important in iteration theorems.
Subproper forcing is a weakening of proper forcing that is still iterable
while including some well known forcing notions which do add countable
sets of ordinals that are not covered by anything in the ground model
including Namba forcing (under CH) and Prikry forcing. One can weaken
other classes of forcing notions in a similar way and the "sub"version of
the countably closed forcing, known as subcomplete forcing, is a
particularly interesting subclass of subproper forcing that was used by
Jensen in several applications including his solution to the extended
Namba problem.
In the first of these talks I will introduce the classes subproper and
subcomplete forcing as well as discuss simplifications of them due to
Fuchs and myself. Time permitting I will discuss new iterations theorems
for these classes reminiscent of similar theorems proved for proper
forcing in the context of the reals and combinatorics on $\omega_1$
($\omega^\omega$-bounding, preservation of Souslin trees etc). In the
second talk I will discuss the forcing axioms for these classes including
their applications and limitations. In particular, time permitting, I will
discuss a recent result, joint with Hiroshi Sakai that the forcing axiom
for subcomplete forcing is compatible with a
$\square_{\omega_1}$-sequence. The take away is a class of strong forcing
axioms that are compatible with a wide variety of behaviour on the level
of the reals and combinatorics on cardinals below the continuum.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, November 24
"Nonstandard models of the reals and symmetrical completeness"
Franz-Viktor Kuhlmann (University of Szczecin, PL)
The notion of power series fields provides an easy method for the
construction of nonstandard models of the ordered field of real numbers. I
will define them, as well as Hahn products, which are their equivalent in
the case of ordered abelian groups. The question arises whether these
power series models can also have additional structures or properties that
we know from the reals. For example, it was shown in joint work with Salma
Kuhlmann and Saharon Shelah that they do not admit exponential functions
which have the same elementary properties as the exponential function on
the reals. In a different direction, the question came up whether they
could support generalizations of Banach’s Fixed Point Theorem. I will
introduce the notions of symmetrically complete ordered fields, abelian
groups and sets and characterize those power series models of the reals
that are symmetrically complete. They indeed admit a (nonarchimedean)
generalization of Banach’s Fixed Point Theorem. Their construction is the
result of joint work with Katarzyna Kuhlmann and Saharon Shelah. It
heavily relies on the analysis of cuts in ordered power series fields and
Hahn products.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom for both talks: If you need the Zoom data and have not received the
meeting link by the day before the talk, please contact
richard.springer@univie.ac.at! (Please direct any other requests about the
seminars and Zoom meeting(s) to vera.fischer@univie.ac.at.)

## Barcelona Set Theory Seminar

Barcelona Logic Seminar

11/17/2022 10:03:46

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: Jiachen Yuan

TITLE: On the cofinality of the least omega_1-strongly compact cardinal

DATE: Wednesday, 23 November 2022

TIME: 16:00 (CET)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat
bagaria@ub.edu

## Nankai Logic Colloquium

Nankai Logic Colloquium

11/14/2022 8:09:06

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon.

Our speaker this week will be Menachem Shlossberg from Reichman University. This talk is going to take place this Friday, Nov. 18 2022, from 4 pm to 5 pm (UTC+8, Beijing time).

Title: Minimality conditions equivalent to the finitude of Fermat and Mersenne primes.

Abstract: It is still open whether there exist infinitely many Fermat primes or

infinitely many composite Fermat numbers. The same question concerning the

Mersenne numbers is also unsolved. Extending some results from [1], we characterize

the Fermat primes and the Mersenne primes in terms of topological minimality of

some matrix groups. This is done by showing, among other things, that if F is a

subfield of a local field of characteristic distinct than 2, then the special upper triangular group ST+(n, F) is minimal precisely when the special linear group SL(n, F) is. We provide criteria for the minimality (and total minimality) of SL(n, F) and ST+(n, F), where F is a subfield of C.

Let $\mathcal F_\pi$ and $\mathcal F_c$ be the set of Fermat primes and the set of composite Fermat numbers, respectively.

As our main result, we prove that the following conditions

are equivalent for $ \mathcal A \in {\mathcal F_\pi, \mathcal F_c} :$

• $\mathcal A$ is finite;

• $\prod_{F_n\in \mathcal A} SL(Fn −1,Q(i))$ is minimal, where Q(i) is the Gaussian rational field;

• $\prod_{F_n\in \mathcal A} ST+(Fn − 1,Q(i))$ is minimal.

Similarly, denote by $\mathcal M_\pi$ and $\mathcal M_c$ the set of Mersenne primes and the set of composite

Mersenne numbers, respectively, and let $ \mathcal B \in {\mathcal M_\pi, \mathcal M_c}$. Then the following

conditions are equivalent:

• $ \mathcal B$ is finite;

• $\prod_{M_p\in \mathcal B} SL(M_p + 1,Q(i))$ is minimal;

• $\prod_{M_p\in \mathcal B} ST+(M_p + 1,Q(i))$ is minimal.

[1] M. Megrelishvili, M. Shlossberg, Minimality of topological matrix groups and Fermat primes, Topol. Appl. 322(2022), doi:10.1016/j.topol.2022.108272.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 10th Nankai Logic Colloquium -- Menachem Shlossberg

Time： 16:00pm, Nov. 18, 2022 (Beijing Time)

Zoom Number：850 1491 3444

Passcode： 596956

Link： https://us02web.zoom.us/j/85014913444?pwd=MnhUTW13MFF3S05raGEzaCs1SXhUQT09

_____________________________________________________________________

Best wishes,

Ming Xiao

## Cross-Alps Logic Seminar (speaker: Annalisa Conversano)

Cross-Alps Logic Seminar

11/14/2022 4:15:19

On Friday 18.11.2022 at 9:00

**Annalisa Conversano** (University of Genoa)

will give a talk on

*Tools of o-minimality in the study of groups*Please refer to the usual webpage of our

LogicGroup for more details and the abstract of the talk.

The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

## This Week in Logic at CUNY

This Week in Logic at CUNY

11/13/2022 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Nov 14, 2022 - - - -

Rutgers Logic Seminar

Monday, November 14, 3:30pm, Rutgers University, Hill 705

Sumun Iyer, Cornell

Dynamics of the Knaster continuum homeomorphism group

Logic and Metaphysics Workshop

Date: Monday, November 14, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Christopher Izgin (Humboldt University).

Title: A new approach to Aristotle’s definitions of truth and falsehood in Metaphysics Γ.7

Abstract: At Metaphysics Γ.7, 1011b26–7, Aristotle defines truth and falsehood as follows: to assert of what is that it is or of what is not that it is not, is true; to assert of what is that it is not or of what is not that it is, is false. In their attempts to interpret the definitions, scholars usually distinguish between the veridical, 1-place, and 2-place uses of ‘to be’. The dominant view holds that all occurrences of ‘is’ in the definientia are interpreted veridically (Kahn 1966, Kirwan 1993, Crivelli 2004, Kimhi 2018, Szaif 2018). So the first truth condition is interpreted as follows: to assert of what is the case that it is the case, is true. I argue against this and side with those who favor a comprehensive—i.e. a jointly 1- and 2-place—interpretation (Matthen 1983, Wheeler 2011), according to which the first truth condition says: to assert of what is (F, exists) that it is (F, exists), is true. It is an open question how this interpretation makes Aristotle’s definitions sufficiently general so as to accommodate all propositional truth-value bearers. I first show that all Aristotelian propositions are reducible to propositions involving a 1- or 2-place ‘is’ and that formal properties, such as quantity and modality, merely modify the ‘is’, thus lending support to the comprehensive interpretation.

- - - - Tuesday, Nov 15, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 15, 7:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

Roman Kossak, CUNY

Generalized quantifiers in arithmetic II

This will be another talk in the MOPA series on the history of the subject.

The work on generalized quantifiers in formal systems of arithmetic was initiated in 1980 by Macintyre, motivated by the search for natural extensions of first-order arithmetic that are immune to the Kirby-Paris-Harrington style independence results. Some open questions posed by Macintyre were solved in a definitive way in 1982 by Schmerl and Simpson and after that Schmerl wrote two more papers on for Peano Arithmetic in the languages with Ramsay stationary quantifiers. Some results of Macintyre were obtained independently by Carl Morgenstern. All these papers, while very well written, are quite technical and not easily accessible for readers who are not familiar with more advanced tools of the model theory of arithmetic. I will survey the results suppressing most technical details. I will also talk about an attempt to use logic with stationary quantifiers to classify ω1-like recursively saturated models of PA.

- - - - Wednesday, Nov 16, 2022 - - - -

- - - - Thursday, Nov 17, 2022 - - - -

- - - - Friday, Nov 18, 2022 - - - -

Set Theory Seminar

CUNY Graduate Center, Friday, November 18, 12:15pm NY time

Virtual: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Brent Cody Virginia Commonwealth University

**Sparse analytic systems**

Given a set S, an S-predictor P is a function that takes as inputs functions of the form f:(−∞,t)→S, where t∈R, and outputs a guess P(f) for what f(t) 'should be.' An S-predictor is good if for all total functions F:R→S the set of t∈R for which the guess P(F↾(−∞,t)) is not equal to F(t) has measure zero. Hardin and Taylor proved that every set S has a good S-predictor and they raised various questions asking about the extent to which the prediction P(f) made by a good predictor might be invariant after precomposing f with various well-behaved functions - this leads to the notion of 'anonymity' of good predictors under various classes of functions. Bajpai and Velleman answered several of Hardin and Taylor's questions and asked: Does there exist, for every set S, a good S-predictor that is anonymous with respect to the strictly increasing analytic homeomorphisms of R? We provide a consistently negative answer to this question by strengthening a result of Erdős, which states that the Continuum Hypothesis is equivalent to the existence of an uncountable family F of (real or complex) analytic functions, such that {f(x):f∈F} is countable for every x. We strengthen Erdős' result by proving that CH is equivalent to the existence of what we call *sparse analytic systems* of functions. This is joint work with Sean Cox and Kayla Lee.

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Friday November 18, 2:00pm-3:30pm, Room 6417

Dima Sinapova Rutgers University

**Dima Sinapova**, Rutgers University

**Prikry sequences and square properties at ℵω**

It is well known that if an inaccessible cardinal κ is singularized to countable cofinality while preserving cardinals, then □κω holds in the outer model. Moreover, this remains true even when relaxing the cardinal preservation assumption a bit. In this talk we focus on when Prikry forcing adds weaker forms of square in a more general setting. We prove abstract theorems about when Prikry forcing with interleaved collapses to bring down the singularized cardinal to ℵω will add a weak square sequence. This can be viewed as a partial positive result to a question of Woodin about whether the failure of SCH at ℵω implies weak square.

Next Week in Logic at CUNY:

- - - - Monday, Nov 21, 2022 - - - -

Logic and Metaphysics WorkshopDate: Monday, November 21, 4.15-6.15 (NY time), GC 7315For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at https://logic.commons.gc.cuny.edu/about/Marko Malink (NYU) and Anubav Vasudevan (University of Chicago).

Title: The origins of conditional logic: Theophrastus on hypothetical syllogisms

Abstract: Łukasiewicz maintained that “the first system of propositional logic was invented about half a century after Aristotle: it was the logic of the Stoics”. In this talk, we argue that the first system of propositional logic was, in fact, developed by Aristotle’s pupil Theophrastus. Theophrastus sought to establish the priority of categorical over propositional logic by reducing various modes of propositional reasoning to categorical form. To this end, he interpreted the conditional “If φ then ψ” as a categorical proposition “A holds of all B”, in which B corresponds to the antecedent φ, and A to the consequent ψ. Under this interpretation, Aristotle’s law of subalternation (A holds of all B, therefore A holds of some B) corresponds to a version of Boethius’ Thesis (If φ then ψ, therefore not: If φ then not-ψ). Jonathan Barnes has argued that this consequence renders Theophrastus’ program of reducing propositional to categorical logic inconsistent. In this paper, we show that Barnes’s objection is inconclusive. We argue that the system developed by Theophrastus is both non-trivial and consistent, and that the propositional logic generated by Theophrastus’ system is exactly the connexive variant of the first-degree fragment of intensional linear logic.

- - - - Tuesday, Nov 22, 2022 - - - -

Models of Peano Arithmetic (MOPA)Tuesday, November 22, 7:00pmVirtual (email Victoria Gitman vgitman@nylogic.org for meeting id) **Joel David Hamkins**, University of Notre Dame

**Pointwise definable and Leibnizian extensions of models of arithmetic and set theory**

I shall introduce a flexible new method showing that every countable model of PA admits a pointwise definable end-extension, one in which every individual is definable without parameters. And similarly for models of set theory, in which one may also achieve the Barwise extension result—every countable model of ZF admits a pointwise definable end-extension to a model of ZFC+V=L, or indeed any theory arising in a suitable inner model. A generalization of the method shows that every model of arithmetic of size at most continuum admits a Leibnizian extension, and similarly in set theory.

- - - - Wednesday, Nov 23, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Saeed Salehi, University of Tabriz.**

Date and Time: ** Wednesday November 23, 2022, TIME TBA.**

Title:** Self-Reference and Diagonalization: their difference and a short history.**

Abstract: What is now called the Diagonal (or the Self-Reference) Lemma, is the statement that for every formula *F*(*x*), with the only free variable *x*, there exists a sentence *σ* such that *σ* is equivalent to the *F* of the Gödel code of *σ*, i.e., *σ* **≡** *F*(**#***σ*); and this equivalence is provable in certain weak arithmetics. This lemma is credited to Gödel (1931), in the special case when *F* is the *un*provability predicate, and to Carnap (1934) in the more general case.

In this talk, we will argue that Gödel-Carnap's original Diagonal Lemma is not the modern formulation and was more similar to, but not exactly identical with, the Strong Diagonal (or Direct Self-Reference) Lemma. This lemma, so-called recently, says that for every formula *F*(*x*), in a sufficiently expressive language, there exists a sentence *σ* such that *σ* is equal to the *F* of the Gödel code of *σ*, i.e., *σ* **=** *F*(**#***σ*); and this equality is provable in sufficiently strong theories. We will attempt at tracking down the first appearance of the modern formulation of the Diagonal Lemma in the equivalent form, also in the strong direct form of equality.

- - - - Thursday, Nov 24, 2022 - - - -

- - - - Friday, Nov 25, 2022 - - - -

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

11/11/2022 14:10:19

Dear all,
The seminar meets on Wednesday November 16th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: David Uhrik -- Characterizing Uncountable Trees using Graphs
I will prove a connection between the uncountable Hadwiger conjecture
and non-special trees. Also characterizations of Aronszajn, Kurepa and
Suslin trees using graphs will be deduced.
Best,
David

## Upcoming Core Model Seminar

Carnegie Mellon Logic Seminar

11/11/2022 9:35:29

TUESDAY, November 15, 2022
Core Model Seminar: 1:30 to 3 PM Eastern, Online, Sandra Müller, TU Wien
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: A stationary-tower-free proof of Sealing, part 2
ORGANIZERS' NOTE: The recording and presentation materials from part 1 are
available in our archive. Please email us to request access.
ABSTRACT: Sealing is a generic absoluteness principle for the theory of
the universally Baire sets of reals introduced by Woodin. It is deeply
connected to the Inner Model Program and plays a prominent role in recent
advances in inner model theory. Woodin showed in his famous Sealing
Theorem that in the presence of a proper class of Woodin cardinals Sealing
holds after collapsing a supercompact cardinal. In the first talk, I will
outline the importance of Sealing and discuss a new and
stationary-tower-free proof of Woodin’s Sealing Theorem that is based on
Sargsyan’s and Trang’s proof of Sealing from iterability. In the second
talk, I will outline the proof of an extension of the SealingTheorem that
gives models in which Theta is regular. This is joint work with Grigor
Sargsyan.

## Barcelona Set Theory Seminar

Barcelona Logic Seminar

11/11/2022 4:15:57

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: Jeffrey Bergfalk

TITLE: The definable content of homological invariants

DATE: Wednesday, 16 November 2022

TIME: 16:00 (CET)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat
bagaria@ub.edu

## Talk by Cristian Calude at CQT on 16 Nov 2022 16:00 hrs

NUS Logic Seminar

11/11/2022 3:26:21

The following seminar is held by Cristian Calude who works in Algorithmic
Randomness as well as in Quantum Computing.
Speaker: Cristian Calude
Date: Wednesday 16 November 2022 at 16:00 hrs
Location: Centre for Quantum Technologies, Seminar Room L3, S15#03-15, NUS
Also as Zoom Meeting: https://nus-sg.zoom.us/j/2817341692
Title: Photonic Ternary Quantum Random Number Generators
Abstract: We construct a class of 3-dimensional photonic quantum
random number generators and prove that each generates maximally
unpredictable digits via measurements that are robust to errors.
In particular, every sequence generated is strongly incomputable;
hence its quality is provable better than that of every pseudo-random
sequence. We also briefly contrast 2-dimensional and 3-dimensional
quantum random number generators, discuss photonic implementations
and show the superiority of the latter ones. These results suggest
that incomputability in physics is real and practically useful.

## (KGRC) seminar talks Tuesday, November 15 and Thursday, November 17

Kurt Godel Research Center

11/10/2022 10:56:43

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Jonathan Schilhan (host: Thilo Weinert) visits the KGRC until November 15.
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC from
November 15 until January 31, 2023 and gives a talk on November 24
(details to be announced at a later time).
David Chodounsky (host: Vera Fischer) visits the KGRC from December 4
until December 8 and gives a talk on December 6 (details to be announced
at a later time).
Jan Hubicka (host: Vera Fischer) visits the KGRC from December 5 until
December 8 and gives a talk on December 6 (details to be announced at a
later time).
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC from December 5 to December 14.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, November 15
"Compactness versus hugeness at successor cardinals, part 2"
Monroe Eskew (KGRC)
There are several ways in which small cardinals can behave like large
ones. One variety is compactness phenomena, such as the tree property,
which characterize when inaccessible cardinals satisfy some strong large
cardinal notions, but can consistently hold at small cardinals such as
$\omega_2$. Another variety is generic embedding properties coming from
saturated ideals or Chang's Conjecture that resemble embeddings associated
with huge cardinals. The known forcing strategies for obtaining
compactness and hugeness properties at small cardinals are very different.
Can they be made to hold simultaneously? In these talks, we present some
combinatorial barriers to combining them, and we show why several forcing
approaches will not work. Hopefully, by narrowing down the space of
possibilities, these negative results will point towards a path to
answering our question.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, November 17
"The Axiom of Choice and large cardinals"
Farmer Schlutzenberg (Universität Münster, DE)
The Axiom of Choice (AC) is mostly accepted by mathematicians, and is
essential in many proofs. However, it seems to be accepted with less
confidence than the other axioms of set theory, probably due to its
non-constructive nature and its various unexpected consequences. Large
cardinals are central axioms in set theory, with compelling consequences
for the universe of sets, not only for "large" sets but also for "small"
ones like real numbers and sets thereof. It turns out that the
relationship between AC and large cardinals is intricate, and not entirely
without conflict. The connections might even be taken to suggest that the
correct picture of the universe of sets is one in which very large
cardinals exist and the full Axiom of Choice must fail. I will survey some
of the recent work in this area. The talk will be aimed at a general logic
audience.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom for both talks: If you need the Zoom data and have not received the
meeting link by the day before the talk, please contact
richard.springer@univie.ac.at! (Please direct any other requests about the
seminars and Zoom meeting(s) to vera.fischer@univie.ac.at.)

## Nankai Logic Colloquium

Nankai Logic Colloquium

11/7/2022 10:06:08

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the morning.

Our speaker this week will be Cesar E. Silva from William College. This talk is going to take place this Friday, Nov 11, 2022, from 9 am to 10 am(UTC+8, Beijing time).

Title: On examples and properties of notions of weak mixing for nonsingular transformations

Abstract: This will largely be a survey talk on several notions of the weak mixing property for nosingular and infinite measure preserving transformations. There are several interesting and seemingly different properties of the weak mixing property that all happen to be equivalent in the case of finite measure preserving transformations. Since the early work of Kakutani and Parry (1963) it has been know that not all these notions are equivalent in the case of infinite measure preserving transformations. We will discuss several of these notions, their implications and counter examples, including some recent work, and topological models for these transformations.

___________________________________________________________________________________________________________________________________________________

This is going to be an online event. Follow the link below to join the Zoom meeting. Please use your real name to join the meeting.

Title： The 9th Nankai Logic Colloquium -- Cesar E. Silva

Time： 9:00am, nov. 11, 2022 (Beijing Time)

Zoom Number：825 9529 2118

Passcode： 475473

Link： https://us02web.zoom.us/j/82595292118?pwd=ZHVGUG9FcUFlSWNqOEN0azlBMk1xdz09

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

11/6/2022 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Nov 7, 2022 - - - -

Rutgers Logic Seminar

Monday, November 7, 3:30pm, Rutgers University, Hill 705

Simon Thomas, Rutgers University

Invariant random subgroups and characters

Nov 7th, Tom Benhamou, UIC

Logic and Metaphysics Workshop

Date: Monday, November 7, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Victoria Gitman (CUNY).

Title: Set theory without the powerset axiom

Abstract: Many natural and useful set-theoretic structures fail to satisfy the Powerset axiom. For example, the universe of sets can be decomposed into the H_alpha-hierarchy, indexed by cardinals alpha, where each H_alpha consists of all sets whose transitive closure has size less than alpha. If alpha is a regular cardinal, then H_alpha satisfies all axioms of ZFC except, maybe, the Powerset axiom (it will only satisfy Powerset if alpha is inaccessible). Class forcing extensions of models of ZFC will often fail to satisfy ZFC, but if the class forcing is nice enough, then it will preserve all the axioms of ZFC except, maybe, the Powerset axiom. Finally, a strong second-order set theory, extending Kelley-Morse by adding a choice principle for classes (Choice Scheme), is bi-interpretable with a strong first-order set theory without the Powerset axiom. Thus working in a strong enough second-order set theory can be reinterpreted as working in a strong first-order set theory in which the Powerset axiom fails. It turns out that simply taking the axioms of ZFC and removing the Powerset axiom does not yield a robust set theory. I will discuss robust (and strong) axiomatizations of set theory without Powerset and how much of the standard set theoretic machinery is still effective even in the strongest theories in the absence of Powerset. Because of the bi-interpretability of a strong set theory without Powerset with Kelley-Morse plus Choice Scheme, these results will have consequences for which set theoretic machinery continues to work in set theories with classes. Time permitting, I will also talk about some unexpectedly strange models of set theory without Powerset.

- - - - Tuesday, Nov 8, 2022 - - - -

Computational Logic Seminar

Fall Semester 2022, Tuesday, November 8, Time 2:00 - 4:00 PM, Room 3310-B

Speaker: Eoin Moore, Graduate Center CUNY

Title: Soundness and completeness results for LEA and probability semantics

Abstract: The goal of the logic of evidence aggregation (LEA) was to describe probabilistic evidence aggregation in the setting of formal logic. However, as noted in that paper, LEA is not complete with respect to probability semantics. This leaves open the tasks to find sound and complete semantics for LEA and a proper axiomatization for probability semantics. We do both. We define a class of basic models called deductive basic models, and show LEA is sound and complete with respect to this class. On the other side, we define an axiomatic system LEA+ extending LEA and show it is sound and complete with respect to probability semantics. Close connections to Propositional Lax Logic are also demonstrated.

Models of Peano Arithmetic (MOPA)

Tuesday, November 8, 7:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

Roman Kossak, CUNY

Generalized quantifiers in arithmetic

This will be another talk in the MOPA series on the history of the subject.

The work on generalized quantifiers in formal systems of arithmetic was initiated in 1980 by Macintyre, motivated by the search for natural extensions of first-order arithmetic that are immune to the Kirby-Paris-Harrington style independence results. Some open questions posed by Macintyre were solved in a definitive way in 1982 by Schmerl and Simpson and after that Schmerl wrote two more papers on for Peano Arithmetic in the languages with Ramsay stationary quantifiers. Some results of Macintyre were obtained independently by Carl Morgenstern. All these papers, while very well written, are quite technical and not easily accessible for readers who are not familiar with more advanced tools of the model theory of arithmetic. I will survey the results suppressing most technical details. I will also talk about an attempt to use logic with stationary quantifiers to classify ω1-like recursively saturated models of PA.

- - - - Wednesday, Nov 9, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Andrei Rodin, University of Lorraine (Nancy, France).**

Date and Time: ** Wednesday November 9, 2022, 7:00 - 8:30 PM.**

Title:** Kolmogorov's Calculus of Problems and Homotopy Type theory.**

Abstract: A. N. Kolmogorov in 1932 proposed an original version of mathematical intuitionism where the concept of problem plays a central role, and which differs in its content from the versions of intuitionism developed by A. Heyting and other followers of L. Brouwer. The popular BHK-semantics of Intuitionistic logic follows Heyting's line and conceals the original features of Kolmogorov's logical ideas. Homotopy Type theory (HoTT) implies a formal distinction between sentences and higher-order constructions and thus provides a mathematical argument in favour of Kolmogorov's approach and against Heyting's approach. At the same time HoTT does not support the constructive notion of negation applicable to general problems, which is informally discussed by Kolmogorov in the same context. Formalisation of Kolmogorov-style constructive negation remains an interesting open problem.

- - - - Thursday, Nov 10, 2022 - - - -

- - - - Friday, Nov 11, 2022 - - - -

Set Theory Seminar

Friday, November 11, 12:15pm NY time

Virtual: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Peter Holy, Technical University of Vienna

**Asymmetric Cut and Choose Games**

We consider the following two player game of infinite length: We are given a starting set X, and the players go by the names 'Cut' and 'Choose'. They take turns making moves, and in each step, Cut partitions a given set into two disjoint pieces, starting from the set X in their first move, and then Choose gets to pick one of the pieces, which is then partitioned into two pieces by Cut in their next move etc. In the end, Choose wins in case the intersection of all of their choices has at least two (distinct) elements.

We will investigate some of the properties of this game — in particular, we will discuss some classic results on when it is possible for one of the players to have a strategy for winning the game. We will then continue to discuss some variations of this game and their relevance to set theory — many central set theoretic notions, such as certain large cardinal properties, notions of distributivity, precipitousness and strategic closure were either known or turned out to be closely connected and often equivalent to the (non-)existence of winning strategies in certain cut and choose games.

This is joint work with Philipp Schlicht, Christopher Turner and Philip Welch (all University of Bristol).

Logic Workshop

(There will be no Logic Workshop seminar today)

Next Week in Logic at CUNY:

- - - - Monday, Nov 14, 2022 - - - -

Rutgers Logic Seminar

Monday, November 14, 3:30pm, Rutgers University, Hill 705

Sumun Iyer, Cornell

Dynamics of the Knaster continuum homeomorphism group

Logic and Metaphysics Workshop

Date: Monday, November 14, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Christopher Izgin (Humboldt University).

Title: A new approach to Aristotle’s definitions of truth and falsehood in Metaphysics Γ.7

Abstract: At Metaphysics Γ.7, 1011b26–7, Aristotle defines truth and falsehood as follows: to assert of what is that it is or of what is not that it is not, is true; to assert of what is that it is not or of what is not that it is, is false. In their attempts to interpret the definitions, scholars usually distinguish between the veridical, 1-place, and 2-place uses of ‘to be’. The dominant view holds that all occurrences of ‘is’ in the definientia are interpreted veridically (Kahn 1966, Kirwan 1993, Crivelli 2004, Kimhi 2018, Szaif 2018). So the first truth condition is interpreted as follows: to assert of what is the case that it is the case, is true. I argue against this and side with those who favor a comprehensive—i.e. a jointly 1- and 2-place—interpretation (Matthen 1983, Wheeler 2011), according to which the first truth condition says: to assert of what is (F, exists) that it is (F, exists), is true. It is an open question how this interpretation makes Aristotle’s definitions sufficiently general so as to accommodate all propositional truth-value bearers. I first show that all Aristotelian propositions are reducible to propositions involving a 1- or 2-place ‘is’ and that formal properties, such as quantity and modality, merely modify the ‘is’, thus lending support to the comprehensive interpretation.

- - - - Tuesday, Nov 15, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 15, 7:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

Roman Kossak, CUNY

Generalized quantifiers in arithmetic II

This will be another talk in the MOPA series on the history of the subject.

The work on generalized quantifiers in formal systems of arithmetic was initiated in 1980 by Macintyre, motivated by the search for natural extensions of first-order arithmetic that are immune to the Kirby-Paris-Harrington style independence results. Some open questions posed by Macintyre were solved in a definitive way in 1982 by Schmerl and Simpson and after that Schmerl wrote two more papers on for Peano Arithmetic in the languages with Ramsay stationary quantifiers. Some results of Macintyre were obtained independently by Carl Morgenstern. All these papers, while very well written, are quite technical and not easily accessible for readers who are not familiar with more advanced tools of the model theory of arithmetic. I will survey the results suppressing most technical details. I will also talk about an attempt to use logic with stationary quantifiers to classify ω1-like recursively saturated models of PA.

- - - - Wednesday, Nov 16, 2022 - - - -

- - - - Thursday, Nov 17, 2022 - - - -

- - - - Friday, Nov 18, 2022 - - - -

Set Theory Seminar

CUNY Graduate Center, Friday, November 18, 12:15pm NY time

Virtual: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Brent Cody Virginia Commonwealth University

Logic Workshop

CUNY Graduate Center

Hybrid: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Friday November 18, 2:00pm-3:30pm, Room 6417

Dima Sinapova Rutgers University

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Wednesday seminar

Prague Set Theory Seminar

11/6/2022 17:37:19

Dear all,
The seminar meets on Wednesday November 9th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jonathan Cancino Manriquez -- More on the combinatorics of
dense subsets of the rationals
We will review some results about cardinal invariants related to the
combinatorics of dense subsets of the rationals, mostly focused on
almost disjoint families of dense subsets of the rationals. In
particular, we will prove a generalization of a theorem of J. Steprans
by proving that some parametrized diamond principles imply that the
almost disjointness number of the boolean algebra P(Q)/nwd is
omega_1(excluding countable maximal antichains) as well as proving that
the additivity of the meager ideal is a lower bound for such cardinal
invariant.
Best,
David

## (KGRC) sminar talks Tuesday, November 8 and Thursday, November 10

Kurt Godel Research Center

11/6/2022 12:59:01

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Will Brian (host: Vera Fischer) visits the KGRC until November 6.
Simone Ramello (host: Martin Hils) visits the KGRC until November 8.
Jonathan Schilhan (host: Thilo Weinert) visits the KGRC until November 15
and gives a talk on November 10 (see below).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC from
November 15 until January 31, 2023 and gives a talk on November 24
(details to be announced at a later time).
David Chodounsky (host: Vera Fischer) visits the KGRC from December 4
until December 8 and gives a talk on December 6 (details to be announced
at a later time).
Jan Hubicka (host: Vera Fischer) visits the KGRC from December 5 until
December 8 and gives a talk on December 6 (details to be announced at a
later time).
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC from December 5 to December 14.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Tuesday, November 8
"Compactness versus hugeness at successor cardinals, part 1"
Monroe Eskew (KGRC)
There are several ways in which small cardinals can behave like large
ones. One variety is compactness phenomena, such as the tree property,
which characterize when inaccessible cardinals satisfy some strong large
cardinal notions, but can consistently hold at small cardinals such as
$\omega_2$. Another variety is generic embedding properties coming from
saturated ideals or Chang's Conjecture that resemble embeddings associated
with huge cardinals. The known forcing strategies for obtaining
compactness and hugeness properties at small cardinals are very different.
Can they be made to hold simultaneously? In these talks, we present some
combinatorial barriers to combining them, and we show why several forcing
approaches will not work. Hopefully, by narrowing down the space of
possibilities, these negative results will point towards a path to
answering our question.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, November 10
"Entire functions and the continuum"
Jonathan Schilhan (University of Leeds, GB)
In the 60's, Erdős showed that the continuum hypothesis is equivalent to
the statement that there is an uncountable family of entire functions on
the complex plane that attains only countably many values at each point.
The argument in fact shows that any family of entire functions, that
attains at each point less values than elements of that family, must have
size continuum. Recently Kumar and Shelah have shown that consistently
such a family exists while the continuum has size $\aleph_{\omega_1}$. We
answer their main open problem by showing that continuum $\aleph_2$ is
possible as well.
This is joint work with T. Weinert.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
Zoom for both talks: If you need the Zoom data and have not received the
meeting link by the day before the talk, please contact
richard.springer@univie.ac.at! (Please direct any other requests about the
seminars and Zoom meeting(s) to vera.fischer@univie.ac.at.)

## Next Core Model Seminar

Carnegie Mellon Logic Seminar

11/4/2022 22:39:43

TUESDAY, November 8, 2022
Core Model Seminar: 1:30 - 3 PM Eastern, Online, Sandra Müller, TU Wien
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: A stationary-tower-free proof of Sealing, part 1
ABSTRACT: Sealing is a generic absoluteness principle for the theory of
the universally Baire sets of reals introduced by Woodin. It is deeply
connected to the Inner Model Program and plays a prominent role in recent
advances in inner model theory. Woodin showed in his famous Sealing
Theorem that in the presence of a proper class of Woodin cardinals Sealing
holds after collapsing a supercompact cardinal. In the first talk, I will
outline the importance of Sealing and discuss a new and
stationary-tower-free proof of Woodin’s Sealing Theorem that is based on
Sargsyan’s and Trang’s proof of Sealing from iterability. In the second
talk, I will outline the proof of an extension of the Sealing Theorem that
gives models in which Theta is regular. This is joint work with Grigor
Sargsyan.

## Logic Seminar Wed 9 Nov 2022 17:00 hrs at NUS by Benjamin T Castle

NUS Logic Seminar

11/3/2022 21:46:31

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 9 November 2022, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Benjamin T Castle
Title: Complex Polynomials up to Interdefinability
`
Abstract: Motivated by recent progress toward Zilber's Restricted
Trichotomy Conjecture, we study reducts of the complex field up to
interdefinability over parameters. Precisely, we will consider structures
of the form (C, P_1,...,P_n), where C is set of complex numbers and
the P_i are polynomial maps of potentially different arities.
Somewhat surprisingly, our main result states that almost all
such structures (in a precise sense) are interdefinable.
The proof uses a mix of tools from geometric stability
theory, combinatorics, and algebraic geometry.
This is joint work with Chieu-Minh Tran.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Logic Seminar Wed 9 Nov 2022 17:00 hrs at NUS by Benjamin T Castle

NUS Logic Seminar

11/3/2022 21:45:24

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 9 November 2022, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Benjamin T Castle
Title: Complex Polynomials up to Interdefinability
`
Abstract: Motivated by recent progress toward Zilber's Restricted
Trichotomy Conjecture, we study reducts of the complex field up to
interdefinability over parameters. Precisely, we will consider structures
of the form (C, P_1,...,P_n), where C is set of complex numbers and
the P_i are polynomial maps of potentially different arities.
Somewhat surprisingly, our main result states that almost all
such structures (in a precise sense) are interdefinable.
The proof uses a mix of tools from geometric stability
theory, combinatorics, and algebraic geometry.
This is joint work with Chieu-Minh Tran.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Logic Seminar Wed 9 Nov 2022 17:00 hrs at NUS by Benjamin T Castle

NUS Logic Seminar

11/3/2022 21:44:46

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 9 November 2022, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Benjamin T Castle
Title: Complex Polynomials up to Interdefinability
`
Abstract: Motivated by recent progress toward Zilber's Restricted
Trichotomy Conjecture, we study reducts of the complex field up to
interdefinability over parameters. Precisely, we will consider structures
of the form (C, P_1,...,P_n), where C is set of complex numbers and
the P_i are polynomial maps of potentially different arities.
Somewhat surprisingly, our main result states that almost all
such structures (in a precise sense) are interdefinable.
The proof uses a mix of tools from geometric stability
theory, combinatorics, and algebraic geometry.
This is joint work with Chieu-Minh Tran.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## UPDATE - This Week in Logic at CUNY

This Week in Logic at CUNY

10/31/2022 11:47:30

Hi everyone,

The Models of Peano Arithmetic (MOPA) talk on November 8th will be given by Roman Kossak (CUNY), on Generalized quantifiers in arithmetic. Apologies for this omission!

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Oct 31, 2022 - - - -

Rutgers Logic Seminar

Monday, October 31, 3:30pm, Rutgers University, Hill 705

Simon Thomas, Rutgers University

Invariant random subgroups and characters

Logic and Metaphysics Workshop

Date: Monday, Oct 31, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Friederike Moltmann (CNRS, Côte d’Azur).

Title: The semantics of special quantification: Higher-order metaphysics and nominalization approaches

Abstract: Prior’s problem consists in the impossibility of replacing clausal complements of most attitude verbs by ‘ordinary’ NPs; only ‘special quantifiers’ that is, quantifiers like something permit a replacement, preserving grammaticality or the same reading of the verb;

(1) a. John claims that he won.

b. ??? John claims a proposition / some thing.

c. John claims something.

In my 2013 book Abstract Objects and the Semantics of Natural Language, I have shown how this generalizes to nonreferential complements of various other intensional predicates and argued for a Nominalization Theory of special quantifiers. In this talk, I will review and extend the range of linguistic generalizations that motivate the Nominalization Theory and show that they pose serious problems for a simple higher-order semantics of special quantifiers. I will outline a new version of the Nominalization Theory for special quantifiers with attitude verbs and address the question whether there can be a unified semantics of special quantifiers for the various contexts in which they display a nominalizing force.

- - - - Tuesday, Nov 1, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 1, 1:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

**Ali Enayat**, University of Gothenburg

**Tightness, solidity, and internal categoricity: Part II**

Inspired by a certain result about PA in Albert Visser's paper 'Categories of theories and interpretations', I introduced the notions of tightness and solidity (of an arbitrary theory) in my paper 'Variations on a Visserian theme'; using them Visser's result can be expressed as: PA is a solid theory (it is easy to show that solidity implies tightness). My aforementioned paper demonstrates that besides PA, certain other canonical theories such as Z_2 (Second Order Arithmetic), ZF, and KM (Kelley-Morse Class Theory) are also solid. The first talk in this series will present : (a) the proofs of solidity of PA and Z_2, and (b) the relationship between Väänänen's notion of internal categoricity with the notions of solidity and tightness. The second part will concentrate on establishing the failure of solidity/tightness of certain subtheories of PA and Z_2, including any subtheory of PA or Z_2 that is finitely axiomatizable.

- - - - Wednesday, Nov 2, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Astra Kolomatskaia, Stony Brook.**

Date and Time: ** Wednesday November 2, 2022, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** The Objective Metatheory of Simply Typed Lambda Calculus.**

Abstract: Lambda calculus is the language of functions. One reduces the application of a function to an argument by substituting the argument for the function's formal parameter inside of the function's body. The result of such a reduction may have further instances of function application. We can write down expressions, such as ((λ f. f f) (λ f. f f)), in which this process does not terminate. In the presence of types, however, one has a normalisation theorem, which effectively states that "programs can be run". One proof of this theorem, which only works for the most elementary of type theories, is to assign some monotone well-founded invariant to a given reduction algorithm. A much more surprising proof proceeds by constructing the normal form of a term by structural recursion on the term's syntactic representation, without ever performing reduction. Such normalisation algorithms fall under the class of Normalisation by Evaluation. Since the accidental discovery of the first such algorithm, it was clear that NbE had some underlying categorical content, and, in 1995, Altenkirch, Hofmann, and Streicher published the first categorical normalisation proof. Discovering this content requires first asking the question “What is STLC?”, perhaps preceded by the question “What is a type theory?”. In this talk we will lay out the details of Altenkirch's seminal paper and explore conceptual refinements discovered in the process of its formalisation in Cubical Agda.

- - - - Thursday, Nov 3, 2022 - - - -

- - - - Friday, Nov 4, 2022 - - - -

Set Theory Seminar

CUNY Graduate Center, Friday, November 4, 12:15pm NY time, room 6495

Hybrid: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

**Corey Switzer**, University of Vienna

**The Special Tree Number**

A tree of height ω1 with no cofinal branch is called *special* if it can be decomposed into countably many antichains or, equivalently if it carries a specializing function: a function f:T→ω so that if f(s)=f(t) then s and t are incomparable in the tree ordering. It is known that there is always a non-special tree of size continuum, but the existence of a smaller one is independent of ZFC. Motivated by this we introduce the special tree number, st, the least size of a tree of height ω1 which is neither non-special nor has a cofinal branch. Classical facts imply that st can be smaller than essentially all well studied cardinal characteristics. Conversely in this talk we will show that st can be larger than a, g, and both the left hand side and bottom row of the Cichon diagram. Thus st is independent of many well known cardinal invariants. Central to this result is an in depth investigation of the types of reals added by the Baumgartner specialization poset which we will discuss as well.

Logic Workshop

CUNY Graduate Center

Hybrid (email Victoria Gitman for meeting id)

Friday November 4, 2:00pm-3:30pm, Room 6417

**Dave Marker**, University of Illinois at Chicago

**Automorphisms of differentially closed fields**

Answering a question of Russell Miller, we show that there are differentially closed fields with no non-trivial automorphisms.

Next Week in Logic at CUNY:

- - - - Monday, Nov 7, 2022 - - - -

Rutgers Logic Seminar

Monday, November 7, 3:30pm, Rutgers University, Hill 705

Simon Thomas, Rutgers University

Invariant random subgroups and characters

Nov 7th, Tom Benhamou, UIC

Logic and Metaphysics Workshop

Date: Monday, November 7, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Victoria Gitman (CUNY).

Title: Set theory without the powerset axiom

Abstract: Many natural and useful set-theoretic structures fail to satisfy the Powerset axiom. For example, the universe of sets can be decomposed into the H_alpha-hierarchy, indexed by cardinals alpha, where each H_alpha consists of all sets whose transitive closure has size less than alpha. If alpha is a regular cardinal, then H_alpha satisfies all axioms of ZFC except, maybe, the Powerset axiom (it will only satisfy Powerset if alpha is inaccessible). Class forcing extensions of models of ZFC will often fail to satisfy ZFC, but if the class forcing is nice enough, then it will preserve all the axioms of ZFC except, maybe, the Powerset axiom. Finally, a strong second-order set theory, extending Kelley-Morse by adding a choice principle for classes (Choice Scheme), is bi-interpretable with a strong first-order set theory without the Powerset axiom. Thus working in a strong enough second-order set theory can be reinterpreted as working in a strong first-order set theory in which the Powerset axiom fails. It turns out that simply taking the axioms of ZFC and removing the Powerset axiom does not yield a robust set theory. I will discuss robust (and strong) axiomatizations of set theory without Powerset and how much of the standard set theoretic machinery is still effective even in the strongest theories in the absence of Powerset. Because of the bi-interpretability of a strong set theory without Powerset with Kelley-Morse plus Choice Scheme, these results will have consequences for which set theoretic machinery continues to work in set theories with classes. Time permitting, I will also talk about some unexpectedly strange models of set theory without Powerset.

- - - - Tuesday, Nov 8, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 8, 7:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

Roman Kossak, CUNY

Generalized quantifiers in arithmetic

This will be another talk in the MOPA series on the history of the subject.

The work on generalized quantifiers in formal systems of arithmetic was initiated in 1980 by Macintyre, motivated by the search for natural extensions of first-order arithmetic that are immune to the Kirby-Paris-Harrington style independence results. Some open questions posed by Macintyre were solved in a definitive way in 1982 by Schmerl and Simpson and after that Schmerl wrote two more papers on for Peano Arithmetic in the languages with Ramsay stationary quantifiers. Some results of Macintyre were obtained independently by Carl Morgenstern. All these papers, while very well written, are quite technical and not easily accessible for readers who are not familiar with more advanced tools of the model theory of arithmetic. I will survey the results suppressing most technical details. I will also talk about an attempt to use logic with stationary quantifiers to classify ω1-like recursively saturated models of PA.

- - - - Wednesday, Nov 9, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Andrei Rodin, University of Lorraine (Nancy, France).**

Date and Time: ** Wednesday November 9, 2022, 7:00 - 8:30 PM.**

Title:** Kolmogorov's Calculus of Problems and Homotopy Type theory.**

Abstract: A. N. Kolmogorov in 1932 proposed an original version of mathematical intuitionism where the concept of problem plays a central role, and which differs in its content from the versions of intuitionism developed by A. Heyting and other followers of L. Brouwer. The popular BHK-semantics of Intuitionistic logic follows Heyting's line and conceals the original features of Kolmogorov's logical ideas. Homotopy Type theory (HoTT) implies a formal distinction between sentences and higher-order constructions and thus provides a mathematical argument in favour of Kolmogorov's approach and against Heyting's approach. At the same time HoTT does not support the constructive notion of negation applicable to general problems, which is informally discussed by Kolmogorov in the same context. Formalisation of Kolmogorov-style constructive negation remains an interesting open problem.

- - - - Thursday, Nov 10, 2022 - - - -

- - - - Friday, Nov 11, 2022 - - - -

Set Theory Seminar

Friday, November 11, 12:15pm NY time

Virtual: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Peter Holy, Technical University of Vienna

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Cross-Alps Logic Seminar (speaker: Jacopo Emmenegger)

Cross-Alps Logic Seminar

10/31/2022 5:07:22

On Friday 04.11.2022 at 16:00

**Jacopo Emmenegger** (University of Genoa)

will give a talk on

*Quotients and equality, (co)algebraically*Please refer to the usual webpage of our

LogicGroup for more details and the abstract of the talk.

The seminar will be held remotely through Webex. Please write to vincenzo.dimonte [at] uniud [dot] it for the link to the event.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2017 'Mathematical logic: models, sets, computability'.

## This Week in Logic at CUNY

This Week in Logic at CUNY

10/30/2022 22:26:23

This Week in Logic at CUNY:

- - - - Monday, Oct 31, 2022 - - - -

Rutgers Logic Seminar

Monday, October 31, 3:30pm, Rutgers University, Hill 705

Simon Thomas, Rutgers University

Invariant random subgroups and characters

Logic and Metaphysics Workshop

Date: Monday, Oct 31, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Friederike Moltmann (CNRS, Côte d’Azur).

Title: The semantics of special quantification: Higher-order metaphysics and nominalization approaches

Abstract: Prior’s problem consists in the impossibility of replacing clausal complements of most attitude verbs by ‘ordinary’ NPs; only ‘special quantifiers’ that is, quantifiers like something permit a replacement, preserving grammaticality or the same reading of the verb;

(1) a. John claims that he won.

b. ??? John claims a proposition / some thing.

c. John claims something.

In my 2013 book Abstract Objects and the Semantics of Natural Language, I have shown how this generalizes to nonreferential complements of various other intensional predicates and argued for a Nominalization Theory of special quantifiers. In this talk, I will review and extend the range of linguistic generalizations that motivate the Nominalization Theory and show that they pose serious problems for a simple higher-order semantics of special quantifiers. I will outline a new version of the Nominalization Theory for special quantifiers with attitude verbs and address the question whether there can be a unified semantics of special quantifiers for the various contexts in which they display a nominalizing force.

- - - - Tuesday, Nov 1, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 1, 1:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

**Ali Enayat**, University of Gothenburg

**Tightness, solidity, and internal categoricity: Part II**

Inspired by a certain result about PA in Albert Visser's paper 'Categories of theories and interpretations', I introduced the notions of tightness and solidity (of an arbitrary theory) in my paper 'Variations on a Visserian theme'; using them Visser's result can be expressed as: PA is a solid theory (it is easy to show that solidity implies tightness). My aforementioned paper demonstrates that besides PA, certain other canonical theories such as Z_2 (Second Order Arithmetic), ZF, and KM (Kelley-Morse Class Theory) are also solid. The first talk in this series will present : (a) the proofs of solidity of PA and Z_2, and (b) the relationship between Väänänen's notion of internal categoricity with the notions of solidity and tightness. The second part will concentrate on establishing the failure of solidity/tightness of certain subtheories of PA and Z_2, including any subtheory of PA or Z_2 that is finitely axiomatizable.

- - - - Wednesday, Nov 2, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Astra Kolomatskaia, Stony Brook.**

Date and Time: ** Wednesday November 2, 2022, 7:00 - 8:30 PM. IN PERSON TALK.**

Title:** The Objective Metatheory of Simply Typed Lambda Calculus.**

Abstract: Lambda calculus is the language of functions. One reduces the application of a function to an argument by substituting the argument for the function's formal parameter inside of the function's body. The result of such a reduction may have further instances of function application. We can write down expressions, such as ((λ f. f f) (λ f. f f)), in which this process does not terminate. In the presence of types, however, one has a normalisation theorem, which effectively states that "programs can be run". One proof of this theorem, which only works for the most elementary of type theories, is to assign some monotone well-founded invariant to a given reduction algorithm. A much more surprising proof proceeds by constructing the normal form of a term by structural recursion on the term's syntactic representation, without ever performing reduction. Such normalisation algorithms fall under the class of Normalisation by Evaluation. Since the accidental discovery of the first such algorithm, it was clear that NbE had some underlying categorical content, and, in 1995, Altenkirch, Hofmann, and Streicher published the first categorical normalisation proof. Discovering this content requires first asking the question “What is STLC?”, perhaps preceded by the question “What is a type theory?”. In this talk we will lay out the details of Altenkirch's seminal paper and explore conceptual refinements discovered in the process of its formalisation in Cubical Agda.

- - - - Thursday, Nov 3, 2022 - - - -

- - - - Friday, Nov 4, 2022 - - - -

Set Theory Seminar

CUNY Graduate Center, Friday, November 4, 12:15pm NY time, room 6495

Hybrid: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

**Corey Switzer**, University of Vienna

**The Special Tree Number**

A tree of height ω1 with no cofinal branch is called *special* if it can be decomposed into countably many antichains or, equivalently if it carries a specializing function: a function f:T→ω so that if f(s)=f(t) then s and t are incomparable in the tree ordering. It is known that there is always a non-special tree of size continuum, but the existence of a smaller one is independent of ZFC. Motivated by this we introduce the special tree number, st, the least size of a tree of height ω1 which is neither non-special nor has a cofinal branch. Classical facts imply that st can be smaller than essentially all well studied cardinal characteristics. Conversely in this talk we will show that st can be larger than a, g, and both the left hand side and bottom row of the Cichon diagram. Thus st is independent of many well known cardinal invariants. Central to this result is an in depth investigation of the types of reals added by the Baumgartner specialization poset which we will discuss as well.

Logic Workshop

CUNY Graduate Center

Hybrid (email Victoria Gitman for meeting id)

Friday November 4, 2:00pm-3:30pm, Room 6417

**Dave Marker**, University of Illinois at Chicago

**Automorphisms of differentially closed fields**

Answering a question of Russell Miller, we show that there are differentially closed fields with no non-trivial automorphisms.

Next Week in Logic at CUNY:

- - - - Monday, Nov 7, 2022 - - - -

Rutgers Logic Seminar

Monday, November 7, 3:30pm, Rutgers University, Hill 705

Simon Thomas, Rutgers University

Invariant random subgroups and characters

Nov 7th, Tom Benhamou, UIC

Logic and Metaphysics Workshop

Date: Monday, November 7, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Victoria Gitman (CUNY).

Title: Set theory without the powerset axiom

Abstract: Many natural and useful set-theoretic structures fail to satisfy the Powerset axiom. For example, the universe of sets can be decomposed into the H_alpha-hierarchy, indexed by cardinals alpha, where each H_alpha consists of all sets whose transitive closure has size less than alpha. If alpha is a regular cardinal, then H_alpha satisfies all axioms of ZFC except, maybe, the Powerset axiom (it will only satisfy Powerset if alpha is inaccessible). Class forcing extensions of models of ZFC will often fail to satisfy ZFC, but if the class forcing is nice enough, then it will preserve all the axioms of ZFC except, maybe, the Powerset axiom. Finally, a strong second-order set theory, extending Kelley-Morse by adding a choice principle for classes (Choice Scheme), is bi-interpretable with a strong first-order set theory without the Powerset axiom. Thus working in a strong enough second-order set theory can be reinterpreted as working in a strong first-order set theory in which the Powerset axiom fails. It turns out that simply taking the axioms of ZFC and removing the Powerset axiom does not yield a robust set theory. I will discuss robust (and strong) axiomatizations of set theory without Powerset and how much of the standard set theoretic machinery is still effective even in the strongest theories in the absence of Powerset. Because of the bi-interpretability of a strong set theory without Powerset with Kelley-Morse plus Choice Scheme, these results will have consequences for which set theoretic machinery continues to work in set theories with classes. Time permitting, I will also talk about some unexpectedly strange models of set theory without Powerset.

- - - - Tuesday, Nov 8, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 8, 7:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

This will be another talk in the MOPA series on the history of the subject.

The work on generalized quantifiers in formal systems of arithmetic was initiated in 1980 by Macintyre, motivated by the search for natural extensions of first-order arithmetic that are immune to the Kirby-Paris-Harrington style independence results. Some open questions posed by Macintyre were solved in a definitive way in 1982 by Schmerl and Simpson and after that Schmerl wrote two more papers on for Peano Arithmetic in the languages with Ramsay stationary quantifiers. Some results of Macintyre were obtained independently by Carl Morgenstern. All these papers, while very well written, are quite technical and not easily accessible for readers who are not familiar with more advanced tools of the model theory of arithmetic. I will survey the results suppressing most technical details. I will also talk about an attempt to use logic with stationary quantifiers to classify ω1-like recursively saturated models of PA.

- - - - Wednesday, Nov 9, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Andrei Rodin, University of Lorraine (Nancy, France).**

Date and Time: ** Wednesday November 9, 2022, 7:00 - 8:30 PM.**

Title:** Kolmogorov's Calculus of Problems and Homotopy Type theory.**

Abstract: A. N. Kolmogorov in 1932 proposed an original version of mathematical intuitionism where the concept of problem plays a central role, and which differs in its content from the versions of intuitionism developed by A. Heyting and other followers of L. Brouwer. The popular BHK-semantics of Intuitionistic logic follows Heyting's line and conceals the original features of Kolmogorov's logical ideas. Homotopy Type theory (HoTT) implies a formal distinction between sentences and higher-order constructions and thus provides a mathematical argument in favour of Kolmogorov's approach and against Heyting's approach. At the same time HoTT does not support the constructive notion of negation applicable to general problems, which is informally discussed by Kolmogorov in the same context. Formalisation of Kolmogorov-style constructive negation remains an interesting open problem.

- - - - Thursday, Nov 10, 2022 - - - -

- - - - Friday, Nov 11, 2022 - - - -

Set Theory Seminar

Friday, November 11, 12:15pm NY time

Virtual: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Peter Holy, Technical University of Vienna

- - - - Other Logic News - - - -- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)-------- ADMINISTRIVIA --------To subscribe/unsubscribe to this list, please email your request to jreitz@nylogic.org.If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org.
## Barcelona Set Theory Seminar

Barcelona Logic Seminar

10/30/2022 3:19:41

Dear All,

Please find attached the announcement of the next Barcelona Set Theory Seminar session.

SPEAKER: Philipp Lücke

TITLE: Rowbottom cardinals and definability

DATE: Wednesday, 2 November 2022

TIME: 16:00 (CEST)

PLACE: Room B1 (UB). The Seminar can also be followed online via Zoom:

Meeting ID: 985 6524 7347

Passcode: 243408

Best regards,

Joan

P.S.: If you do not wish to receive any more announcements, please send an email to

bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria

ICREA Research Professor

Universitat de Barcelona

Departament de Matemàtiques i Informàtica

Gran Via de les Corts Catalanes 585

08007 Barcelona

Catalonia

Phone: +34 93 402 1609

joan.bagaria@icrea.cat
bagaria@ub.edu

## Core Model Seminar on Tuesday

Carnegie Mellon Logic Seminar

10/29/2022 19:00:05

TUESDAY, November 1, 2022
Core Model Seminar: 1:30 - 3 PM Eastern, Online, Derek Levinson,
University of California, Los Angeles
Join Zoom Meeting:
https://cmu.zoom.us/j/97749733438?pwd=Yk5PcSsvekptWWxMNUhCU2pFbzA0Zz09
Meeting ID: 977 4973 3438
Passcode: 457791
TITLE: Unreachability of Pointclasses in $L(R)$, part 2
ABSTRACT: We present Hjorth's proof that there is no sequence of distinct
$\Sigma^1_2$ sets of length $\delta^1_2$. Then we prove in $L(R)$ if
$\Gamma$ is an inductive-like pointclass then there is no sequence of
distinct $\Gamma$ sets of length $\delta_\Gamma^+$.
ORGANIZERS' NOTE: If you'd like access to our archives of presentation
materials and recordings, please ask Ernest Schimmerling.

## (KGRC) two(!) seminar talks on Thursday, November 3

Kurt Godel Research Center

10/28/2022 10:55:49

The KGRC welcomes as guests:
Martin Hils (host: Matthias Aschenbrenner) visits the KGRC until March 31,
2023 and gives a talk on January 19, 2023 (details to be announced at a
later time).
Franz-Viktor Kuhlmann (host: Matthias Aschenbrenner) visits the KGRC from
November 1 until January 31, 2023 and gives a talk on November 24 (details
to be announced at a later time).
Will Brian (host: Vera Fischer) visits the KGRC from November 1 to
November 6 and gives two talks (see below).
Simone Ramello (host: Martin Hils) visits the KGRC from November 3 to
November 8.
David Chodounsky (host: Vera Fischer) visits the KGRC from December 4
until December 8 and gives a talk on December 6 (details to be announced
at a later time).
Jan Hubicka (host: Vera Fischer) visits the KGRC from December 5 until
December 8 and gives a talk on December 6 (details to be announced at a
later time).
Stefan Ludwig (hosts: Martin Hils and Matthias Aschenbrenner) visits the
KGRC from December 5 to December 14.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, November 3
"Covering versus partitioning with Polish spaces"
Will Brian (UNC Charlotte, US)
A topological space is Polish if it is second countable and completely
metrizable. We may think of these as the small, or "essentially countable"
members of the category of completely metrizable spaces. In this talk, we
explore the question of whether, given a completely metrizable space $X$,
it is possible to cover $X$ with fewer Polish spaces than it can be
partitioned into. Surprisingly, this question not only turns out to be
independent of ZFC, but proving its independence requires large cardinal
axioms. I will sketch some of the ideas that go into one direction of this
independence proof. Specifically, I will describe how a version of the
model-theoretic transfer principle called Chang's Conjecture implies that
there is a completely metrizable space that can be covered with fewer
Polish spaces than it can be partitioned into.
Time and Place
Talk at 3:00pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Kolingasse 14-16
1090 Wien
1st floor
Seminar room 10
For details about how to join the Zoom session, please see the end of this
message.
* * *
Set Theory Research Seminar
Kurt Gödel Research Center
Thursday, November 3
(Please note the unusual day, time and place!)
"Partitioning the real line into Borel sets"
Will Brian (UNC Charlotte, US)
I will sketch a proof that, assuming $0^\dagger$ does not exist, if there
is a partition of the real line $\mathbb{R}$ into $\aleph_\omega$ Borel
sets, then there is also a partition of $\mathbb{R}$ into
$\aleph_{\omega+1}$ Borel sets. (And the same is true for any singular
cardinal of countable cofinality in place of $\aleph_\omega$.) This
contrasts starkly with the situation for successor-of-successor cardinals,
where the spectrum of possible sizes of partitions of $\mathbb{R}$ into
Borel sets can seemingly be made completely arbitrary. For example, given
any $A \subseteq \omega$ with $0, 1 \in A$, there is a forcing extension
in which $A = \{n < \omega :$ there is a partition of $\mathbb{R}$ into
$\aleph_n$ Borel sets$\}$.
Time and Place
Talk at 4:45pm in hybrid mode, in person as well as via Zoom. (Students at
Uni Wien are required to attend in person.)
Universität Wien
Institut für Mathematik
Oskar-Morgenstern-Platz 1
1090 Wien
2nd floor
Seminar room 14
Zoom: If you need the Zoom data and have not received the meeting link by
the day before the talk, please contact richard.springer@univie.ac.at!
(Please direct any other requests about the seminars and Zoom meeting(s)
to vera.fischer@univie.ac.at.)

## Wednesday seminar

Prague Set Theory Seminar

10/27/2022 11:27:36

Dear all,
The seminar meets on Wednesday November 2nd at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Please note that the open days of the Institute will take place next
week, so expect children running around and other minor inconveniences.
Program: Chris Lambie Hanson -- Partition relations on Polish spaces
We study partition relations on Polish spaces, asserting that arbitrary
colorings of products of uncountable Polish spaces have "large"
monochromatic subsets (for example, products of somewhere dense subsets
on which the coloring is constant). We will discuss situations in which
such partition relations provably do or do not hold and will prove a
sharp result indicating the effect of such relations on the value of the
continuum. Time and interest permitting, we will also discuss
connections with the Halpern-Lauchli theorem and its variations. This is
joint work with Andy Zucker.
Best,
David

## Logic Seminar Wed 2 Nov 2022 17:00 hrs at NUS by Wu Guohua

NUS Logic Seminar

10/26/2022 21:46:22

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 02 November 2022, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Wu Guohua
Title: Ring constructions: axioms needed
Abstract: Many constructions in rings involve applications
of various axioms, which guarantee the existence of wanted
objects. In this talk, I will present examples of such
constructions, and show how these axioms are applied
and really needed.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Logic Seminar 26 October 2022 17:00 hrs at NUS by Sun Mengzhou

NUS Logic Seminar

10/25/2022 18:24:01

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 26 October 2022, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Sun Mengzhou
Title: End extensions of weak arithmetic theories
Abstract: Paris and Kirby showed that a countable model satisfies
B Sigma_{n+2} if and only if it has an (n+2)-elementary proper
end extension. Later Kaufman asked whether we can always extend
countable models of B Sigma_{n+2} to some model of B Sigma_{n+1}.
We briefly discuss what we have now related to this question and
what is the difficulty here.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## UPDATE - This Week in Logic at CUNY

This Week in Logic at CUNY

10/24/2022 10:29:51

Hi everyone,

Just an update - David Marker's talk in the Logic Workshop will take place on Friday, November 4th (it was erroneously marked as this Friday, October 28).

Apologies for this error,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Oct 24, 2022 - - - -

Rutgers Logic Seminar

Monday, October 24, 3:30pm, Rutgers University, Hill 705

Corey Switzer, University of Vienna

The Special Tree Number

Logic and Metaphysics Workshop

Date: Monday, Oct 24, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Tomorrow, Monday, October 24th, 4.15-6.15 (NY time)

Speaker: Rohit Parikh (CUNY)

Speaker Medium: In-person at the Graduate Center, Room 7314 (you may also attend virtually).

Title: A measure of group coherence

Abstract: The Stanford Encyclopedia of Philosophy has an article on Social Epistemology and also one on group rights. Wikipedia has an article on group coherence. Clearly, groups are important and that importance is acknowledged. But what is missing is a measure of group coherence or as I shall say, groupiness. The Democratic party is a group but the Squad is a more coherent subgroup and works more closely with each other. The bees in a beehive work coherently with each other but it is not clear if this coherence is buttressed by common beliefs. The purpose of this talk, and of this project is to propose a measure of groupiness, investigate its properties, ask about the extent to which it enables group action, and about the extent to which it comports with epistemic logic and with the theory of information.

- - - - Tuesday, Oct 25, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, October 25, 1:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

**Ali Enayat**, University of Gothenburg

**Tightness, solidity, and internal categoricity**

Inspired by a certain result about PA in Albert Visser's paper 'Categories of theories and interpretations', I introduced the notions of tightness and solidity (of an arbitrary theory) in my paper 'Variations on a Visserian theme'; using them Visser's result can be expressed as: PA is a solid theory (it is easy to show that solidity implies tightness). My aforementioned paper demonstrates that besides PA, certain other canonical theories such as Z_2 (Second Order Arithmetic), ZF, and KM (Kelley-Morse Class Theory) are also solid. The first talk in this series will present : (a) the proofs of solidity of PA and Z_2, and (b) the relationship between Väänänen's notion of internal categoricity with the notions of solidity and tightness. The second part will concentrate on establishing the failure of solidity/tightness of certain subtheories of PA and Z_2, including any subtheory of PA or Z_2 that is finitely axiomatizable.

Computational Logic Seminar

Tuesday, October 25, Time 2:00 - 4:00 PM, Room 3310-B,

For a zoom link contact

SArtemov@gmail.comSpeaker: Sergei Artemov, Graduate Center CUNY

Title: How to Prove, and Not to Prove, Consistency

Abstract: The consistency of a formal theory is a sequential property **C** = {C_0, C_1, ... C_n, ...}, where each C_n states that the n-th derivation does not contain a contradiction. For proving **C** in a theory **T**, Hilbert suggested (i) finding a procedure that given n builds a **T**-proof of C_n and (ii) proving in **T** that this procedure always works.

However, for Peano Arithmetic PA, the traditional way here has been to compress **C** into a single arithmetical formula Consis(PA) and apply the Second Gödel Incompleteness theorem, stating the unprovability of Consis(PA) in PA, to claim the unprovability of **C** in PA. This chain of reasoning is fundamentally flawed: one can only conclude that (a compressed form of) consistency is not provable in a FINITE fragment of PA whereas PA is known to be (much) stronger than any of its finite fragments.

Following the original Hilbert's approach, we were able to show that the consistency property of PA is indeed provable in PA. These findings dismantle a foundational “impossibility paradigm”: *there exists no consistency proof of a system that can be formalized in the system itself.* (Encyclopaedia Britannica, Article "Metalogic," 2000).

- - - - Wednesday, Oct 26, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417

Speaker: ** Ross Street, Macquarie University.**

Date and Time: ** Wednesday October 26, 2022, 7:00 - 8:30 PM.**

Title:** The core groupoid can suffice.**

Abstract: Let V be the monoidal category of modules over a commutative ring R. I am interested in categories A for which there is a groupoid G such that the functor categories [A,V] and [G,V] are equivalent. In particular, G could be the core groupoid of A; that is, the subcategory with the same objects and with only the invertible morphisms. Every category A can be regarded as a V-category (that is, an R-linear category), denoted RA, with the same objects and with hom R-module RA(a,b) free on the homset A(a,b). Indeed, RA is the free V-category on A so that the V-functor category [RA,V] is the ordinary functor category [A,V] with the pointwise R-linear structure. In these terms, we are interested in when RA and RG are Morita equivalent V-categories. In my joint work with Steve Lack on Dold-Kan-type equivalences, we had many examples of this phenomenon. However, the example of Nick Kuhn, where A is the category of finite vector spaces over a fixed finite field F with all F-linear functions and G is the general linear groupoid over F, does not fit our theory. Yet the ``kernel'' of the equivalence is of the same type. The present work shows that the category theory behind the Kuhn result also covers our Dold-Kan-type setting. I plan to start with a baby example which highlights the ideas.

I am grateful to Nick Kuhn and Ben Steinberg for their patient email correspondence with me on this topic.

- - - - Thursday, Oct 27, 2022 - - - -

- - - - Friday, Oct 28, 2022 - - - -

Set Theory Seminar

CUNY Graduate Center, Friday, October 28, 12:15pm NY time

Virtual: Please email Victoria Gitman (

vgitman@nylogic.org) for meeting id.

Andreas Lietz, University of Münster

**Forcing 'NSω1 is ω1-dense' from Large Cardinals - A Journey guided by the Stars: Part II**

An ideal I on ω1 is ω1-dense if (P(ω1)/I)+ has a dense subset of size ω1. We prove, assuming large cardinals, that there is a semiproper forcing P so thatVP⊨‘NSω1 is ω1-dense'.This answers a question of Woodin positively. Our general strategy is based on the observation that replacing the role of Pmax in Woodin's axiom (∗) by Qmax results in an axiom Qmax−(∗) which implies ‘NSω1 is ω1-dense'.

We proceed in three steps: First we define and motivate a new forcing axiom QM and then modify the Asperó-Schindler proof of ‘MM++⇒(∗)' to show ‘QM⇒Qmax−(∗)'. Finally, assuming a supercompact limit of supercompact cardinals exists, we construct a semiproper partial order forcing QM. This last step involves proving two new iteration theorems both of which allow for forcings killing stationary sets.

Logic Workshop

CUNY Graduate Center

Hybrid (email Victoria Gitman for meeting id)

Friday October 28, 2:00pm-3:30pm, Room 6417

**Ideal Independence, Filters and Maximal Sets of Reals**

A family I⊆[ω]ω is called ideal independent if given any finite, distinct A,B0,...,Bn−1∈I, the set A∖⋃i<nBi is infinite. In other words, the ideal generated by I∖{A} does not contain A for any A∈I. The least size of a maximal (with respect to inclusion) ideal independent family is denoted smm and has recently been tied to several interesting questions in cardinal characteristics and Boolean algebra theory. In this talk we will sketch our new proof that this number is ZFC-provably greater than or equal to the ultrafilter number – the least size of a base for a non-principal ultrafilter on ω. The proof is entirely combinatorial and relies only on a knowledge of ultrafilters and their properties. Time permitting, we will also discuss some interesting new applications of ideal independent families to topology via a generalization of Mrowka spaces usually studied for almost disjoint families. This is joint work with Serhii Bardyla, Jonathan Cancino and Vera Fischer.

Next Week in Logic at CUNY:

- - - - Monday, Oct 31, 2022 - - - -

Rutgers Logic Seminar

Monday, October 31, 3:30pm, Rutgers University, Hill 705

Simon Thomas, Rutgers University

Invariant random subgroups and characters

Logic and Metaphysics Workshop

Date: Monday, Oct 31, 4.15-6.15 (NY time), GC 7315

For meeting information (including zoom link for those wishing to attend remotely), please sign up for our mailing list at

https://logic.commons.gc.cuny.edu/about/Friederike Moltmann (CNRS, Côte d’Azur).

Title: The semantics of special quantification: Higher-order metaphysics and nominalization approaches

Abstract: Prior’s problem consists in the impossibility of replacing clausal complements of most attitude verbs by ‘ordinary’ NPs; only ‘special quantifiers’ that is, quantifiers like something permit a replacement, preserving grammaticality or the same reading of the verb;

(1) a. John claims that he won.

b. ??? John claims a proposition / some thing.

c. John claims something.

In my 2013 book Abstract Objects and the Semantics of Natural Language, I have shown how this generalizes to nonreferential complements of various other intensional predicates and argued for a Nominalization Theory of special quantifiers. In this talk, I will review and extend the range of linguistic generalizations that motivate the Nominalization Theory and show that they pose serious problems for a simple higher-order semantics of special quantifiers. I will outline a new version of the Nominalization Theory for special quantifiers with attitude verbs and address the question whether there can be a unified semantics of special quantifiers for the various contexts in which they display a nominalizing force.

- - - - Tuesday, Nov 1, 2022 - - - -

Models of Peano Arithmetic (MOPA)

Tuesday, November 1, 1:00pm

Virtual (email Victoria Gitman

vgitman@nylogic.org for meeting id)

**Ali Enayat**, University of Gothenburg

**Tightness, solidity, and internal categoricity: Part II**

Inspired by a certain result about PA in Albert Visser's paper 'Categories of theories and interpretations', I introduced the notions of tightness and solidity (of an arbitrary theory) in my paper 'Variations on a Visserian theme'; using them Visser's result can be expressed as: PA is a solid theory (it is easy to show that solidity implies tightness). My aforementioned paper demonstrates that besides PA, certain other canonical theories such as Z_2 (Second Order Arithmetic), ZF, and KM (Kelley-Morse Class Theory) are also solid. The first talk in this series will present : (a) the proofs of solidity of PA and Z_2, and (b) the relationship between Väänänen's notion of internal categoricity with the notions of solidity and tightness. The second part will concentrate on establishing the failure of solidity/tightness of certain subtheories of PA and Z_2, including any subtheory of PA or Z_2 that is finitely axiomatizable.

- - - - Wednesday, Nov 2, 2022 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York, Room 6417