## This Week in Logic at CUNY

This Week in Logic at CUNY

5/19/2024 22:30:00

This Week in Logic at CUNY:

- - - - Monday, May 20, 2024 - - - -

- - - - Tuesday, May 21, 2024 - - - -

- - - - Wednesday, May 22, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Emilio Minichiello , The CUNY Graduate Center.**

Date and Time: ** Wednesday May 22, 2024, 7:00 - 8:30 PM. IN PERSON TALK!**

Title:** Presenting Profunctors.**

Abstract: In categorical database theory, profunctors are ubiquitous. For example, they are used to define schemas in the algebraic data model. However, they can also be used to query and migrate data. In this talk, we will discuss an interesting phenomenon that arises when trying to model profunctors in a computer. We will introduce two notions of profunctor presentations: the UnCurried and Curried presentations. They are modeled on thinking of profunctors as functors P: C^op x D -> Set and as functors P: C^op -> Set^D, respectively. Semantically of course, these are equivalent, but their syntactic properties are quite different. The UnCurried presentations are more intuitive and easier to work with, but they carry a fatal flaw: there does not exist a semantics-preserving composition operation of UnCurried presentations that also preserves finiteness. Therefore we introduce the Curried presentations and show that they remedy this flaw. In the process, we characterize which UnCurried Presentations can be made Curried, and discuss some applications. This talk will be based off of this recent preprint which is joint work with Gabriel Goren Roig and Joshua Meyers.

- - - - Thursday, May 23, 2024 - - - -

- - - - Friday, May 24, 2024 - - - -

Next Week in Logic at CUNY:

- - - - Monday, May 27, 2024 - - - -

- - - - Tuesday, May 28, 2024 - - - -

- - - - Wednesday, May 29, 2024 - - - -

- - - - Thursday, May 30, 2024 - - - -

- - - - Friday, May 31, 2024 - - - -

- - - - 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@citytech.cuny.edu.

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jreitz@citytech.cuny.edu.

## KGRC Talks - May 24

Kurt Godel Research Center

5/17/2024 4:16:21

KGRC/Institute of Mathematics invites you to the following talks:
Set Theory Seminar
Kolingasse 14--16, 1090, 1st floor, SR 10,
Thursday, May 23, 11:30am--1:00pm, hybrid mode
"Concentrated sets and $\gamma$-sets in the Miller model"
V. Haberl (TU Wien)
Bartoszyński and Halbeisen conjectured that in the Miller model there
exists a concentrated set of reals of size $\mathfrak{c} = \omega_2$.
Let us recall that a set $X\subseteq 2^\omega$ is concentrated if there
exists a countable $Q\subseteq X$ such that $|X\setminus U|\leq \omega$
for every open set $U \subseteq 2^\omega$ with $Q\subseteq U$.
In our talk we shall present the main ideas of the proof that this
conjecture is false. Concentrated sets are canonical examples of
Rothberger spaces of reals. We want to analyse the possible
cardinalities of sets of reals satisfying selection principles in the
Miller model. To avoid triviality we are interested in the totally
imperfect cases, i.e. spaces that do not contain a copy of the Cantor
space. Note that since $\mathfrak{d}$-concentrated sets are totally
imperfect Menger spaces, there are such spaces of size continuum (since
$\mathfrak{d} = \mathfrak{c}$). We shall sketch the proof that for the
strongest selection principle, the $\gamma$-set property, only
cardinality atmost $\omega_1$ is possible. We hope that the tools of our
results can be used as a prototype for the non-existence of Rothberger
sets of reals with cardinality $\mathfrak{c}$. The goal would be to
prove the same for Hurewicz totally imperfect sets of reals, the latter
being a weaker property than Rothberger in the Miller model.
The talk will be based on a recent joint work with Piotr Szewczak and
Lyubomyr Zdomskyy.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at.
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Logic Colloquium
Oskar-Morgenstern-Platz 1, 1090, 2nd floor, HS 11,
Thursday, May 23, 3:00pm--3:50pm, hybrid mode
"Centenary of the Menger Conjecture"
P. Szewczak (Cardinal Stefan Wyszyński University, Warsaw, PL)
In 1924, Menger observed that any metric space $X$ which is
\emph{$\sigma$-compact} (i.e., it is a countable union of its compact
subsets) has such a property that for any basis $\mathcal{B}$ of $X$,
there are sets $B_0,B_1,\ldots\in\mathcal{B}$, such that
$\mathrm{lim}_{n\to\infty}\mathrm{diam}(B_n)=0$ and $X=\bigcup_{n\in
\omega }B_n$.
Menger conjectured that the above property characterizes
$\sigma$-compactness in the class of metric spaces. Soon thereafter
Hurewicz reformulated the Menger property without using a metric: for
any sequence $\mathcal{U}_0,\mathcal{U}_1,\ldots$ of open covers of a
given topological space, there are finite sets
$\mathcal{F}_1\subseteq\mathcal{U}_0,
\mathcal{F}_1\subseteq\mathcal{U}_1,\ldots$ such that the family
$\bigcup_{n\in\omega}\mathcal{F}_n$ is an open cover of the space.In
that way, the definition of the Menger property was extended on all
topological spaces. By the results of Fremlin--Miller and
Bartoszyński--Tsaban, there is in ZFC a subspace of the real line which
is Menger but no $\sigma$-compact.
The aim of the talk is to present an overview of the Menger property
which is one of the most influential property in the topological
selections theory and it has many connections to topology, set-theory
and function spaces.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at.
Please direct any questions about this talk to
matthias.aschenbrenner@univie.ac.at.
* * * * * * * * *
Video recordings available so far of the Set Theory Seminar:
May, 14: O. Zindulka (Czech Technical U, Prague, CZ) "Combinatorics of
Uniform Covers"
https://ucloud.univie.ac.at/index.php/s/2BBqLQZy7TownbM
May, 16: C.B. Switzer (U Wien) "Baumgartner's Axiom and Cardinal
Characteristics: A Sparse Look at Dense Sets of Reals III"
https://ucloud.univie.ac.at/index.php/s/BtQZfJS54fSnTJM
Video recordings available so far of the Logic Colloquium:
May, 16: R. Sklinos (Chinese Academy of Sciences, Beijing, CN)
"First-order sentences in random groups"
https://ucloud.univie.ac.at/index.php/s/59BbzjWPdGiCB8x
* * * * * * * * *
Updates at https://kgrc.univie.ac.at/eventsnews/.
--
Institute of Mathematics (Kurt Goedel Research Center, Logic)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## Wednesday seminar

Prague Set Theory Seminar

5/16/2024 4:21:35

Dear all,
The seminar meets on Wednesday May 22nd at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Next week there will also be an extra session of the Set Theory and
Analysis seminar on Friday May 24th at 14:00, talk delivered by John
Truss. (As well as an interesting talk on Tuesday morning.) See here:
https://www.math.cas.cz/index.php/events/seminar/6
Program (Wednesday): Jindřich Zapletal -- Partition properties of omega
one without choice
I will show that certain natural partition properties of omega one which
follow from the axiom of determinacy still hold in balanced extensions
of the Solovay model, making them consistent with such objects as Vitali
sets or ultrafilters.
Best,
David

## 53rd Nankai Logic Colloquium

Nankai Logic Colloquium

5/16/2024 0:21:51

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon, but at an irregular time, as we have two speakers this week.

Our speakers this week will be Yang Zheng and Ruiwen Li, both from Nankai University. This talk is going to take place this Friday, May 17th, from 2:30 pm to 5 pm (UTC+8, Beijing time). The first talk is starting at 2:30pm, and the second talk is starting at 4pm. Both talks are offline/online hybrid.

Yang Zheng:

Title: On equivalence relations induced by Polish groups

Abstract: In this talk, we introduce Borel orbit equivalence relations, denoted by E(G), which can well-describe the structures and properties of a Polish group G from the perspective of Borel reduction.

Given a Polish group G, let E(G) be the right coset equivalence relation $G^\omega/c(G)$, where c(G) is the group of all convergent sequences in G. We shall present the following results: for a non-trivial Polish group G, we have that: (1) G is a countable group iff $E(G)\sim_B E_0$; (2) G is TSI non-archimedean uncountable iff $E(G)\sim_B E^\omega_0$; and (3) G is non-archimedean iff $E(G)\leq_B =^+$. In particular, $E(S_\infty)\sim_B =^+$ holds. Moreover, we will provide some Rigid Theorems and a Pre-rigid Theorem on TSI Polish groups, which can transform the existence problem of Borel reduction between E(G) equivalence relations, into the existence problem of well-behaved continuous homomorphisms between Polish groups. This is a joint work with Longyun Ding.

Ruiwen Li:

Title: Topological Type and Conjugacy Relation on Minimal Systems

Abstract: The complexity of conjugacy relation on minimal systems under Borel reducibility is a well-known question in descriptive set theory. In this talk, by analyzing the conjugacy relation on Oxtoby systems, I'll define an equivalence relation named topological type, this relation gives a lower bound of conjugacy complexity of minimal systems and shows that the conjugacy relation on minimal systems cannot be classified by countable structures. Moreover, when considering the isomorphism relation of pointed minimal systems, the topological type relation describes its exact complexity.

__________________________________________________________________________________________________________________________

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

Title ：The 53th Nankai Logic Colloquium

Time ：14:30pm, May. 17, 2024(Beijing Time)

Zoom Number ： 371 037 9317

Passcode ：477893

Link ：https://zoom.us/j/3710379317?pwd=WEpLTjBtV1B2SHZaaFpnWU1qNzJVQT09&omn=92298090494

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best wishes,

Ming Xiao

## UPDATE: This Week in Logic at CUNY

This Week in Logic at CUNY

5/13/2024 10:25:31

Hi everyone,

Note the addition of two talks in the NYC Category Theory Seminar, May 15 and May 22.

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, May 13, 2024 - - - -

- - - - Tuesday, May 14, 2024 - - - -

Computational Logic Seminar

Spring 2024 (online)

Tuesday, May 14, Time 2:00 - 4:00 PM (EDT)

zoom link: ask Sergei Artemov

sartemov@gmail.com**Speaker**: *Hans van Ditmarsch, **CNRS, IRIT, University of Toulouse, France*

**Title: ***Epistemic logic and simplicial complexes*

**Abstract: **All my working life as a logician epistemic logic came with Kripke models, in particular the kind for multiple agents with equivalence relations to interpret knowledge. Sure enough, I knew about enriched Kripke models, like subset spaces, or with topologies. But at some level of abstraction you get back your standard Kripke model. Imagine my surprise, around 2018, that there is an entirely dual sort of structure on which the epistemic logical language can be interpreted and that results in the same S5 logic: simplicial complexes. Instead of points that are worlds and links labeled with agents, we now have points that are agents and links labeled with worlds. Or, instead of edges (links), triangles, tetrahedrons, etcetera, that represent worlds. Simplicial complexes are well-known within combinatorial topology and have wide usage in distributed systems to model (a)synchronous computation. The link with epistemic modal logic is recent, spreading out from Mexico City and Paris to other parts of the world, like Vienna and Bern. Other logics are relevant too, for example KB4, in order to encode crashed processes/agents. Other epistemics are relevant too, and in particular distributed knowledge, which facilitates further generalizations from simplicial complexes to simplicial sets. It will be my pleasure to present my infatuation with this novel development connecting epistemic logic and distributed computing. Suggested introductory reading is:

https://arxiv.org/abs/2002.08863

https://link.springer.com/chapter/10.1007/978-3-030-75267-5_1

Knowledge and Simplicial Complexes

Hans van Ditmarsch, Eric Goubault, Jeremy Ledent, Sergio Rajsbaum

https://drops.dagstuhl.de/entities/document/10.4230/DagRep.13.7.34

Epistemic and Topological Reasoning in Distributed Systems (Dagstuhl Seminar 23272)

Armando Castañeda, Hans van Ditmarsch, Roman Kuznets, Yoram Moses, Ulrich Schmid

Section 4.3 Representing Epistemic Attitudes via Simplicial Complexes

- - - - Wednesday, May 15, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Raymond Puzio.**

Date and Time: ** Wednesday May 15, 2024, 7:00 - 8:30 PM. IN-PERSON!**

Title:** Uniqueness of Classical Retrodiction.**

Abstract: In previous talks at this Category seminar and at the Topology, Geometry and Physics seminar, Arthur Parzygnat showed how Bayesian inversion and its generalization to quantum mechanics may be interpreted as a functor on a suitable category of states which satisfies certain axioms. Such a functor is called a retrodiction and Parzygnat and collaborators conjectured that retrodiction is unique. In this talk, I will present a proof of this conjecture for the special case of classical probability theory on finite state spaces.

In this special case, the category in question has non-degenerate probability distributions on finite sets as its objects and stochastic matrices as its morphisms. After preliminary definitions and lemmas, the proof proceeds in three main steps.

In the first step, we focus on certain groups of automorphisms of certain objects. As a consequence of the axioms, it follows that these groups are preserved under any retrodiction functor and that the restriction of the functor to such a group is a certain kind of group automorphism. Since this group is isomorphic to a Lie group, it is easy to prove that the restriction of a retrodiction to such a group must equal Bayesian inversion if we assume continuity. If we do not make that assumption, we need to work harder and derive continuity "from scratch" starting from the positivity condition in the definition of stochastic matrix.

In the second step, we broaden our attention to the full automorphism groups of objects of our category corresponding to uniform distributions. We show that these groups are generated by the union of the subgroup consisting of permutation matrices and the subgroup considered in the first step. From this fact, it follows that the restriction of a retrodiction to this larger group must equal Bayesian inversion.

In the third step, we finally consider all the objects and morphisms of our category. As a consequence of what we have shown in the first two steps and some preliminary lemmas, it follows that retrodiction is given by matrix conjugation. Furthermore, Bayesian inversion is the special case where the conjugating matrices are diagonal matrices. Because the hom sets of our category are convex polytopes and a retrodiction functor is a continuous bijection of such sets, a retodiction must map polytope faces to faces. By an algebraic argument, this fact implies that the conjugating matrices are diagonal, answering the conjecture in the affirmative.

Paper.

- - - - Thursday, May 16, 2024 - - - -

*** FINAL EXAMS WEEK BEGINS - CUNY GRADUATE CENTER ***

- - - - Friday, May 17, 2024 - - - -

Next Week in Logic at CUNY:

- - - - Monday, May 20, 2024 - - - -

- - - - Tuesday, May 21, 2024 - - - -

- - - - Wednesday, May 22, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Emilio Minichiello , The CUNY Graduate Center.**

Date and Time: ** Wednesday May 22, 2024, 7:00 - 8:30 PM. IN PERSON TALK!**

Title:** Presenting Profunctors.**

Abstract: In categorical database theory, profunctors are ubiquitous. For example, they are used to define schemas in the algebraic data model. However, they can also be used to query and migrate data. In this talk, we will discuss an interesting phenomenon that arises when trying to model profunctors in a computer. We will introduce two notions of profunctor presentations: the UnCurried and Curried presentations. They are modeled on thinking of profunctors as functors P: C^op x D -> Set and as functors P: C^op -> Set^D, respectively. Semantically of course, these are equivalent, but their syntactic properties are quite different. The UnCurried presentations are more intuitive and easier to work with, but they carry a fatal flaw: there does not exist a semantics-preserving composition operation of UnCurried presentations that also preserves finiteness. Therefore we introduce the Curried presentations and show that they remedy this flaw. In the process, we characterize which UnCurried Presentations can be made Curried, and discuss some applications. This talk will be based off of this recent preprint which is joint work with Gabriel Goren Roig and Joshua Meyers.

- - - - Thursday, May 23, 2024 - - - -

- - - - Friday, May 24, 2024 - - - -

- - - - 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@citytech.cuny.edu.

If you have a logic-related event that you would like included in future mailings, please email

jreitz@citytech.cuny.edu.

## This Week in Logic at CUNY

This Week in Logic at CUNY

5/12/2024 22:31:00

Hi everyone,

This will be our last edition of "This Week in Logic at CUNY" for the Spring 2024 semester -- regular mailings will resume in late August. Special updates may be sent for events that arise in the meantime.

Wishing you a happy and productive summer!

All the best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, May 13, 2024 - - - -

- - - - Tuesday, May 14, 2024 - - - -

Computational Logic Seminar

Spring 2024 (online)

Tuesday, May 14, Time 2:00 - 4:00 PM (EDT)

zoom link: ask Sergei Artemov

sartemov@gmail.com**Speaker**: *Hans van Ditmarsch, **CNRS, IRIT, University of Toulouse, France*

**Title: ***Epistemic logic and simplicial complexes*

**Abstract: **All my working life as a logician epistemic logic came with Kripke models, in particular the kind for multiple agents with equivalence relations to interpret knowledge. Sure enough, I knew about enriched Kripke models, like subset spaces, or with topologies. But at some level of abstraction you get back your standard Kripke model. Imagine my surprise, around 2018, that there is an entirely dual sort of structure on which the epistemic logical language can be interpreted and that results in the same S5 logic: simplicial complexes. Instead of points that are worlds and links labeled with agents, we now have points that are agents and links labeled with worlds. Or, instead of edges (links), triangles, tetrahedrons, etcetera, that represent worlds. Simplicial complexes are well-known within combinatorial topology and have wide usage in distributed systems to model (a)synchronous computation. The link with epistemic modal logic is recent, spreading out from Mexico City and Paris to other parts of the world, like Vienna and Bern. Other logics are relevant too, for example KB4, in order to encode crashed processes/agents. Other epistemics are relevant too, and in particular distributed knowledge, which facilitates further generalizations from simplicial complexes to simplicial sets. It will be my pleasure to present my infatuation with this novel development connecting epistemic logic and distributed computing. Suggested introductory reading is:

https://arxiv.org/abs/2002.08863

https://link.springer.com/chapter/10.1007/978-3-030-75267-5_1

Knowledge and Simplicial Complexes

Hans van Ditmarsch, Eric Goubault, Jeremy Ledent, Sergio Rajsbaum

https://drops.dagstuhl.de/entities/document/10.4230/DagRep.13.7.34

Epistemic and Topological Reasoning in Distributed Systems (Dagstuhl Seminar 23272)

Armando Castañeda, Hans van Ditmarsch, Roman Kuznets, Yoram Moses, Ulrich Schmid

Section 4.3 Representing Epistemic Attitudes via Simplicial Complexes

- - - - Wednesday, May 15, 2024 - - - -

- - - - Thursday, May 16, 2024 - - - -

*** FINAL EXAMS WEEK BEGINS - CUNY GRADUATE CENTER ***

- - - - Friday, May 17, 2024 - - - -

Next Week in Logic at CUNY:

- - - - Monday, May 20, 2024 - - - -

- - - - Tuesday, May 21, 2024 - - - -

- - - - Wednesday, May 22, 2024 - - - -

- - - - Thursday, May 23, 2024 - - - -

- - - - Friday, May 24, 2024 - - - -

- - - - 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@citytech.cuny.edu.

If you have a logic-related event that you would like included in future mailings, please email

jreitz@citytech.cuny.edu.

## 120 Years of Choice, Leeds, 8–12 July 2024

Conference

5/12/2024 1:00:00

120 Years of Choice, 8–12 July, 2024
This is a reminder for our conference 120 Years of Choice that will take
place at the University of Leeds from 8th to 12th of July.
For those that are still undecided, the scope of the conference is not
limited to the Axiom of Choice and we will have a wide variety of speakers
coming from different areas. The same of course also applies to poster
submissions.
Registration is still open until June 20th (20/06/2024), but we would like
to ask all participants to register at their earliest convenience, so that
we can plan accordingly.
We have now extended the submission deadline for posters to May 31st
(31/05/2024). Let us reiterate that we may be able to offer some financial
support to those presenting a poster. We encourage any early career
researchers to apply.
For registration see more details at https://120ac.set-theory.info or
email us at 120ac@leeds.ac.uk.

Tagged: Assaf Rinot, Assaf Shani, Azul Fatalini, David Asperó, Diana Montoya, Inbar Oren, John Steel, Kameryn WilliamsLorenzo Notaro, Martina Iannella, Moti Gitik, Natasha Dobrinen, Sheila Miller Edwards, Siiri Kivimäki, Toshimichi Usuba, Yair Hayut, Philipp Schlicht

## Set Theory in the United Kingdom, Oxford, 16 May 2024

Conference

5/12/2024 0:00:00

STUK 13 ("Set Theory in the United Kingdom") will take place at the
Mathematical Institute of the University of Oxford on Thursday, 16 May
2024. We have already secured István Juhász and Thilo Weinert as invited
speakers who both plan to be there in person.
https://www.dpmms.cam.ac.uk/~dbl25/STUK/
The schedule will be roughly as for the past meetings: we start in the
late morning, have one talk before lunch, then lunch, then two more talks,
and then ample time for "informal presentations" where everyone can and
should speak to present themselves, their open questions, their research
project, or their results.

Tagged: István Juhász, Julia Millhouse, Thilo Weinert

## Wednesday seminar

Prague Set Theory Seminar

5/11/2024 3:07:29

Dear all,
The seminar meets on Wednesday May 15th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jonathan Cancino Manriquez -- Basically generated ultrafilters
This is a continuation of the last talk. We will recall and extend some
facts that were already presented. Then we will prove some results on
the existence of basically generated ultrafilters.
Best,
David

## KGRC Set Theory Talks - May 12-17

Kurt Godel Research Center

5/8/2024 12:17:52

KGRC/Institute of Mathematics invites you to the following talks:
SetTheory Seminar
Kolingasse 14–16, 1090, 1st floor, SR 10, hybrid mode
TUESDAY, May 14, 3:00pm–4:30pm
”Combinatorics of Uniform Covers”
O. Zindulka (Czech Technological University, Prague, CZ)
We look at diagonalization properties for sequences of various flavors
of uniform covers of separable metric spaces and we describe them with
game-theoretic and Ramsey-like partition properties. Applications
include strong measure zero, null-additive and meager-additive sets in
Polish groups, Menger-bounded spaces etc.
Some highlights: a link to fractal measures and how it can help with
calculation of cardinal invariants; Galvin-Mycielski-Solovay Theorem in
various contexts;a solution to a Scheepers problem regarding products of
strong measure zero spaces.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Set Theory Seminar
Kolingasse 14--16, 1090, 1st floor, SR 10,
Thursday, May 16, 11:30am--1:00pm, hybrid mode
"Baumgartner's Axiom and Cardinal Characteristics: A Sparse Look at
Dense Sets of Reals III"
C. B. Switzer (U Wien)
Mini-course (25.04.2024-16.05.2024, 3 lectures) - 3rd lecture:
Given a cardinal $\kappa$, a set of reals $A\subseteq \mathbb R$ is
$\kappa$-dense if its intersection with any open interval has size
$\kappa$. Baumgartner's axiom (BA)---proved consistent by Baumgartner in
1973---states that all $\aleph_1$-dense sets of reals are order
isomorphic with the induced linear order from $\mathbb R$. This is the
most straightforward generalization to the uncountable of Cantor's proof
that all countable dense linear orders without endpoints are order
isomorphic. BA has variations to other topological spaces---given a
topological space $X$, a subset $A \subseteq X$ is $\kappa$-dense if its
intersection with each non-empty open subset has size $\kappa$. The
axiom BA($X$) states that given any two $\aleph_1$-dense subsets of $X$,
say $A$ and $B$, there is an autohomeomorphism of $X$ mapping $A$ onto
$B$. In this parlance BA is equivalent to BA ($\mathbb R$). Surprisingly
BA is not equivalent to BA ($\mathbb R^n$) for any finite $1< n <
\omega$. In fact BA does not follow from Martin's Axiom
(Abraham-Rubin-Shelah) though BA($\mathbb R^n$) does (in fact from
$\mathfrak{p} > \aleph_1$) for each $n > 1$ (Steprāns-Watson).
In these three lectures I will discuss these ideas and some related ones
including the question of when BA($X$) implies BA($Y$) for Polish spaces
$X$ and $Y$. Central to these questions are the role of cardinal
characteristics including the celebrated theorem of Todorčević that BA
implies $\mathfrak b > \aleph_1$ as well as a recent, higher dimensional
analogue of this result that for any $n < \omega$ BA($\mathbb R^n$)
implies $\mathfrak b > \aleph_1$ (S.-Steprāns). There are many beautiful
open problems in this area and I plan to make discussing them a focal
point of the talks. The talks will start slowly and should be accessible
to students. Time permitting, the final talk will include some new
results. If and when these results are presented, they are joint work
with Juris Steprāns.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Video recordings available of the Set Theory Workshop ”Compactness and
Cardinal Invariants,
Vienna, May 3, 2024:
C. Agostini (TU Wien), "On Nagata-Smirnov spaces and metrizability-like
properties"
https://ucloud.univie.ac.at/index.php/s/DpQiNFzdqxpptfT
S. Bardyla (U Wien), "Bohr compactification of discrete groups and Schur
ultrafilters"
https://ucloud.univie.ac.at/index.php/s/3cpFpjNMZ6z5ejG
J. Cancino (Czech Academy of Sciences, Prague, CZ), "Some results on
Tukey types of ultrafilters on the natural numbers"
https://ucloud.univie.ac.at/index.php/s/8eiGqEsGCszYEG6
M. Iannella (TU Wien), "Descriptive consequences of rank-into-rank axioms"
https://ucloud.univie.ac.at/index.php/s/rSjEQYjTzbdE6os
Ch. Lambie-Hanson (Czech Academy of Sciences, Prague, CZ), "Hajnal-Máté
graphs and club guessing"
https://ucloud.univie.ac.at/index.php/s/pzpofnbPMyJZ9WY
A. Medini (TU Wien), "A complete classification of the zero-dimensional
homogeneous spaces under determinacy"
https://ucloud.univie.ac.at/index.php/s/QfZ8ccqaKk5anwH
J.M. Millhouse (U Wien), "Projectively definable mad families of
multiple sizes"
https://ucloud.univie.ac.at/index.php/s/kGPsfCgqJBQPKPk
Š. Stejskalová (Charles U, Prague, CZ), "Forcing over a free Suslin tree"
https://ucloud.univie.ac.at/index.php/s/HTpXbwd9cd5zcRJ
C.B. Switzer (U Wien), "Baumgartner’s axiom and its higher dimensional
versions"
https://ucloud.univie.ac.at/index.php/s/224KHG2b9nJgp3w
T. van der Vlugt (TU Wien), "The horizontal direction"
https://ucloud.univie.ac.at/index.php/s/nSGmaJNbzpoHAoN
* * * * * * * * *
Updates at https://kgrc.univie.ac.at/eventsnews/)
--
Institute of Mathematics (Kurt Goedel Research Center, Logic)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## This Week in Logic at CUNY

This Week in Logic at CUNY

5/5/2024 22:07:18

This Week in Logic at CUNY:

- - - - Monday, May 6, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, May 6, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Lorenzo Rossi (Turin)

Title: Alethic pluralism and Kripkean truth

Abstract: According to alethic pluralism, there is more than one way of being true: truth is not unique, in that there is a plurality of truth properties each of which pertains to a specific domain of discourse. This paper shows how such a plurality can be represented in a coherent formal framework by means of a Kripke-style construction that yields intuitively correct extensions for distinct truth predicates. The theory of truth it develops can handle at least three crucial problems that have been raised in connection with alethic pluralism: mixed compounds, mixed inferences, and semantic paradoxes.

Note: This is joint work with Andrea Iacona (Turin) and Stefano Romeo (Turin).

- - - - Tuesday, May 7, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Virtual (email Victoria Gitman (

vgitman@gmail.com) for meeting id)

Tuesday, May 7, 1pm

**Ali Enayat**, University of Gothenburg

**Tarski's undefinability of truth theorem strikes again**

Tarski's undefinability of truth theorem has two versions, the first one deals with truth itself, takes some effort to prove, and is a descendant of the Epimenides (liar) paradox. The second one deals with the related concept of satisfaction, has a one-line proof, and is a descendent of Russell's paradox. This talk is about the first one, which appeared in the 1953 monograph 'Undecidable Theories' by Tarski, Mostowski, and Robinson; it was employed there to show the essential undecidability of consistent theories that can represent all recursive functions (a strong form of the Gödel-Rosser incompleteness theorem). I will present Tarski's original 1953 formulation (which differs from the common formulation in modern expositions) and will explain how it was used in my recent work with Albert Visser to show that no consistent completion of a sequential theory whose signature is finite is axiomatizable by a collection of sentences of bounded quantifier-alternation-depth. A variant of this result was proved independently by Emil Jeřábek, as I will explain. Our proof method has a pedagogical dividend since it allows one to replace the cryptic Gödel-Carnap fixed point lemma with the perspicuous undefinability of truth theorem in the proof of the Gödel-Rosser incompleteness theorem.

Computational Logic Seminar

Spring 2024 (online)

Tuesday, May 7, Time 2:00 - 4:00 PM (EDT)

zoom link: ask Sergei Artemov

sartemov@gmail.comSpeaker: SREEHARI KALLOORMANA, Graduate Center CUNY

Title: Formal Argumentation Theory and Argumentation Logics.

Abstract: Deductive Logic is monotonic, in that when the set of premises grows, the set of conclusions grows as well. Since the 1980s, Non-monotonic Logics, where this does not hold, have been studied to model commonsense reasoning, especially in the field of artificial intelligence. In this talk, we will be looking at argument-based nonmonotonic logics, which formalize the notion of attack and defeat in the field of argumentation theory. We will consider briefly abstract argumentation frameworks and the various semantic notions proposed by P.M. Dung in 1995, followed by logic-based structured argumentation frameworks `a la John Pollock, and the more recent ASPIC framework. Various notions of argument attack/defeat fundamental to argumentation, such as rebuttal, undercutting, and undermining, will be discussed. We will then introduce and discuss the idea of reasoning about argumentation using Justification logic, by introducing priority orderings over formulas and justification terms.

- - - - Wednesday, May 8, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: Juan Orendain, Case Western Univeristy.

Date and Time: Wednesday May 8, 2024, 7:00 - 8:30 PM. ZOOM TALK.

Title:** Canonical squares in fully faithful and absolutely dense equipments.**

Abstract: Equipments are categorical structures of dimension 2 having two separate types of 1-arrows -vertical and horizontal- and supporting restriction and extension of horizontal arrows along vertical ones. Equipments were defined by Wood in [W] as 2-functors satisfying certain conditions, but can also be understood as double categories satisfying a fibrancy condition as in [Sh]. In the zoo of 2-dimensional categorical structures, equipments nicely fit in between 2-categories and double categories, and are generally considered as the 2-dimensional categorical structures where synthetic category theory is done, and in some cases, where monoidal bicategories are more naturally defined.

In a previous talk in the seminar, I discussed the problem of lifting a 2-category into a double category along a given category of vertical arrows, and how this problem allows us to define a notion of length on double categories. The length of a double category is a number that roughly measures the amount of work one needs to do to reconstruct the double category from a bicategory along its set of vertical arrows.

In this talk I will review the length of double categories, and I will discuss two recent developments in the theory: In the paper [OM] a method for constructing different double categories from a given bicategory is presented. I will explain how this construction works. One of the main ingredients of the construction are so-called canonical squares. In the preprint [O] it is proven that in certain classes of equipments -fully faithful and absolutely dense- every square that can be canonical is indeed canonical. I will explain how from this, it can be concluded that fully faithful and absolutely dense equipments are of length 1, and so they can be 'easily' reconstructed from their horizontal bicategories.

References:

[O] Length of fully faithful framed bicategories. arXiv:2402.16296.

[OM] J. Orendain, R. Maldonado-Herrera, Internalizations of decorated bicategories via π-indexings. To appear in Applied Categorical Structures. arXiv:2310.18673.

[W] R. K. Wood, Abstract Proarrows I, Cahiers de topologie et géométrie différentielle 23 3 (1982) 279-290.

[Sh] M. Shulman, Framed bicategories and monoidal fibrations. Theory and Applications of Categories, Vol. 20, No. 18, 2008, pp. 650–738.

- - - - Thursday, May 9, 2024 - - - -

- - - - Friday, May 10, 2024 - - - -

Model Theory Seminar

CUNY Graduate Center

Friday May 10, 12:30pm NY time, Room: 6495

Alf Dolich, CUNY

**The decidability of the rings Z/mZ**

In this expository talk I will discuss recent work of Derakhshan and Macintyre on the decidability of the common theory of the rings Z/mZ as m varies through the natural numbers m>1.

Logic Workshop

CUNY Graduate Center

Friday May 10, 2:00pm-3:30pm, Room 5417

**Roman Kossak**, CUNY

**The lattice problem for models of arithmetic**

The lattice problem for models of PA is to determine which lattices can be represented either as lattices of elementary substructures of a model of PA or, more generally, which can be represented as lattices of elementary substructures of a model N that contain a given elementary substructure M of N.

Since the 1970's, the problem generated much research with highly nontrivial results with proofs combining specific methods in the model theory of arithmetic with lattice theory and various combinatorial theorems. The problem has a definite answer in the case of distributive lattices, and, despite much effort, there are still many open questions in the nondistributive case. I will briefly survey some early results and present a few proofs that illustrate the difference between the distributive and nondistributive cases.

Next Week in Logic at CUNY:

- - - - Monday, May 13, 2024 - - - -

- - - - Tuesday, May 14, 2024 - - - -

- - - - Wednesday, May 15, 2024 - - - -

- - - - Thursday, May 16, 2024 - - - -

*** FINAL EXAMS WEEK BEGINS - CUNY GRADUATE CENTER ***

- - - - Friday, May 17, 2024 - - - -

- - - - 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@citytech.cuny.edu.

If you have a logic-related event that you would like included in future mailings, please email

jreitz@citytech.cuny.edu.

## Logic Seminar 8 May 2024 17:00 hrs at NUS

NUS Logic Seminar

5/3/2024 2:34:26

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 08 May 2024, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-04
Speaker: Vittorio Cipriano
Title: Characterizing different notions of learnability of structures
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
In this talk, we combine computable structure theory and inductive inference
to study learning of families of structures. All the structures we consider
are relational and countable and all the families of structures we consider
are at most countable. The framework we use was defined in a series of papers
by Bazhenov, Fokina, Koetzing and San Mauro. In a nutshell, the framework
models the scenario in which, given a family of structures K, a learner
receives more and more information about the atomic diagram of a copy of
some A in K and, at each stage, is required to output a conjecture about
the isomorphism type of such a structure. In this context, a natural
criterion to consider is Ex-learning in which we require the learner
to stabilize to the correct conjecture after finitely many steps.
Together with Bazhenov and San Mauro we gave a descriptive set-theoretic
characterization of Ex-learning. Namely, we showed that a family of
structures is Ex-learnable if and only if the corresponding isomorphism
problem continuously reduces to E_0, the equivalence relation of eventual
agreement on infinite binary sequences. Replacing E_0 with other
equivalence relations, one obtains a hierarchy to rank such isomorphism
problems. That is, a family of structures K is E-learnable,
for an equivalence relation E, if there is a continuous reduction
from the isomorphism problem associated with K to E.
We aim to obtain model-theoretic characterization of E-learning
for different equivalence relations E. Some characterizations are
already present in the literature: here we show that a family of structures
K such that for any A_i, A_j in K there is a Sigma_n^{inf} formula satisfied
by A_i but not by A_j is E-learnable if and only if E is the (iteration
of the) Friedman-Stanely jump of the identity either on natural numbers
or on Cantor space. We also show that other learning criteria coming from
the classical setting of inductive inference of formal languages
or recursive functions have a nice model-theoretic characterization.
This talk collects joint works with Bazhenov, Jain, Marcone, San Mauro and Stephan.

## Fwd: 9 FMP: przestrzenie Banacha: geometria i operatory

Wrocław Set Theory Seminar

5/1/2024 3:26:46

Szymonie, rozeslij to, proszę do wszystkich z seminarium. To Jest wiadomość od Tomka Kanii (który prosi o informowanie wszystkich zainteresowanych) w sprawie sesji Przestrzenie Banacha, ale na liście konferencji jest też sesja Teoria Mnogości. Pozdrawiam, G

---------- Forwarded message ---------

Od:

**Tomasz Kania** <tomasz2.kania@uj.edu.pl>Date: wt., 30 kwi 2024 o 21:10

Subject: 9 FMP: przestrzenie Banacha: geometria i operatory

okazuje się, że sesja z przestrzeni Banacha się odbędzie (nie jest jednak jeszcze jasne, którego dnia konferencji); jeżeli nadal wyrażasz zainteresowanie przyjazdem, bardzo proszę o przesłanie abstraktu na:

Abstrakty - 9. Forum Matematyków Polskich (us.edu.pl)

(oraz idealnie potwierdzenie emailowe do mnie, że udało Ci się posłać).

## Set Theory Workshop "Compactness and Cardinal Invariants" Vienna, May 2, 2024

Conference

5/3/2024

Set Theory Workshop at OMP and Kolingasse
Together with our Czech research partners we invite you to this Workshop.
Time and location:
Morning session 9:00-12:00, Oskar-Morgenstern-Platz 1, SR 6, 1st fl.
Afternoon session 14:00-17:55, Kolingasse 14-16, SR 1, 1st fl.
Zoom info: Please contact petra.czarnecki@univie.ac.at
Program:
09 : 00 − 9 : 30 Andrea Medini
09 : 35 − 10 : 05 Šárka Stejskalová
10 : 05 − 10 : 40 COFFEE
10 : 40 − 11 : 10 Corey Switzer
11 : 15 − 11 : 45 Serhii Bardyla
12 : 00 − 14 : 00 LUNCH
14 : 00 − 14 : 30 Chris Lambie-Hanson
14 : 35 − 15 : 05 Jonathan Cancino
15 : 05 − 15 : 40 COFFEE
15 : 40 − 16 : 10 Julia Millhouse
16 : 15 − 16 : 45 Tristan van der Vlugt
16 : 50 − 17 : 20 Martina Iannella
17 : 25 − 17 : 55 Claudio Agostini
Organizer:
Vera Fischer (U Wien)
Radek Honzik (Charles University, Prague, CZ)
If you have any questions, please write to the organizers.
For more information see the program.

Tagged: Andrea Medini, Šárka Stejskalová, Corey Switzer, Serhii Bardyla, Chris Lambie-Hanson, Jonathan Cancino, Julia Millhous, Tristan van der Vlugt, Martina Iannella, Claudio Agostini

## UPDATE: This Week in Logic at CUNY

This Week in Logic at CUNY

4/29/2024 19:49:19

Hi everyone,

Note the addition of a talk by Benjamin Prudhomme in the Computational Logic Seminar on Tuesday 4/30.

All best,

Jonas

This Week in Logic at CUNY:

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Monday, Apr 29, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 29, 3:30pm Hill Center, Hill 705

Gabe Goldberg, Berkeley

Generalizations of the Ultrapower Axiom

Logic and Metaphysics Workshop

Date: Monday, April 29, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Anandi Hattiangadi (Stockholm).

Title: Physicalism, intentionality and normativity: The essential explanatory gap

Abstract: In this paper, I present an explanatory gap argument against the view that the semantic facts are fully grounded in the physical facts. Unlike traditional explanatory gap arguments, which stem from the failure of analytic reductive explanation, the explanatory gap I point to stems from the failure of metaphysical explanation. I argue for the following theses. (i) Physicalist grounding claims are metaphysically necessary, if true. (ii) To be explanatorily adequate, these grounding claims must be deducible from facts about essence. (iii) Semantico-physical grounding claims are possibly false, not (only) because they are conceivably false, but because they cannot be deduced from facts about essence. (iv) Semantic properties are essentially weakly normative: it lies in their natures to have correctness conditions and subjectively rationalize—rather than merely cause—behaviour. This gives rise to an explanatory gap that indicates that the semantic facts are not fully grounded in the physical facts.

- - - - Tuesday, Apr 30, 2024 - - - -

Computational Logic Seminar

Spring 2024 (online)

Tuesday, April 30

Time 2:00 - 4:00 PM (EDT)

zoom link: ask Sergei Artemov

sartemov@gmail.comSpeaker: Benjamin PrudHomme, Graduate Center CUNY

Title: On Game Theory and Epistemic Logic

Abstract: Review of basic game theory and epistemic game theory concepts, including strictly competitive games, pure and mixed strategy Nash equilibria, rationalizability, models of knowledge, distinction between mutual and common knowledge. Review of proofs of when a game has a Nash equilibrium, Nash's Theorem, Muddy Children Problem. Discussions of current and potential future efforts to utilize logic in developing a more comprehensive theory of pure strategy solutions.

- - - - Wednesday, May 1, 2024 - - - -

- - - - Thursday, May 2, 2024 - - - -

- - - - Friday, May 3, 2024 - - - -

Model Theory Seminar

CUNY Graduate Center

Friday May 3, 12:30pm NY time, Room: 6495

Athar Abdul-Quader, Purchase College

Genericity in models of arithmetic

In this talk, I plan to explore a few notions of 'genericity' in the context of models of arithmetic. I will recall the notion of genericity borrowed from set-theory, used by Simpson to prove that every countable model of PA has an expansion to a pointwise definable model of PA*. I will then explore other notions of genericity inspired by more model-theoretic contexts. One such notion is 'neutrality': in a model M, we say an undefinable set X is neutral if the definable closure relation in (M, X) is the same as in M. Another notion, inspired by work done on model-theoretic genericity by Chatzidakis and Pillay, is called CP-genericity. I will explore these notions and outline some results, including: (1) every model of PA has a neutral set which is not CP-generic, (2) every countable model of PA has a CP-generic which is not neutral (and in fact, fails neutrality spectacularly: ie, we can find a CP-generic where the expansion is pointwise definable), and (3) every countable model of PA has a neutral CP-generic. This talk touches on work contained in two papers, one of which was joint work with Roman Kossak, and the other was joint work with James Schmerl.

Set Theory Seminar

CUNY Graduate Center

Friday, May 3, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

**Spencer Unger**, University of Toronto

**Iterated ultrapower methods in analysis of Prikry type forcing**

We survey some old and new results in singular cardinal combinatorics whose proofs can be phrased in terms of iterated ultrapowers and ask a few questions.

Logic Workshop

CUNY Graduate Center

Friday May 3, 2:00pm-3:30pm, Room 5417

**Christian Wolf**, CUNY

**Computability of entropy and pressure on compact symbolic spaces beyond finite type**

In this talk we discuss the computability of the entropy Htop(X) and topological pressure Ptop(ϕ) on compact shift spaces X and continuous potentials ϕ:X→R. This question has recently been studied for subshifts of finite type (SFTs) and their factors (Sofic shifts). We develop a framework to address the computability of the entropy pressure on general shift spaces and apply this framework to coded shifts. In particular, we prove the computability of the topological pressure for all continuous potentials on S-gap shifts, generalized gap shifts, and Beta shifts. We also construct shift spaces which, depending on the potential, exhibit computability and non-computability of the topological pressure. We further show that the generalized pressure function (X,ϕ)↦Ptop(X,ϕ|X) is not computable for a large set of shift spaces X and potentials ϕ. Along the way of developing these computability results, we derive several ergodic-theoretical properties of coded shifts which are of independent interest beyond the realm of computability. The topic of the talk is joint work with Michael Burr (Clemson U.), Shuddho Das (Texas Tech) and Yun Yang (Virginia Tech).

Next Week in Logic at CUNY:

- - - - Monday, May 6, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, May 6, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Lorenzo Rossi (Turin)

Title: Alethic pluralism and Kripkean truth

Abstract: According to alethic pluralism, there is more than one way of being true: truth is not unique, in that there is a plurality of truth properties each of which pertains to a specific domain of discourse. This paper shows how such a plurality can be represented in a coherent formal framework by means of a Kripke-style construction that yields intuitively correct extensions for distinct truth predicates. The theory of truth it develops can handle at least three crucial problems that have been raised in connection with alethic pluralism: mixed compounds, mixed inferences, and semantic paradoxes.

Note: This is joint work with Andrea Iacona (Turin) and Stefano Romeo (Turin).

- - - - Tuesday, May 7, 2024 - - - -

- - - - Wednesday, May 8, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: Juan Orendain, Case Western Univeristy.

Date and Time: Wednesday May 8, 2024, 7:00 - 8:30 PM. ZOOM TALK.

Title: Canonical squares in regularly framed bicategories.

- - - - Thursday, May 9, 2024 - - - -

- - - - Friday, May 10, 2024 - - - -

Logic Workshop

CUNY Graduate Center

Friday May 10, 2:00pm-3:30pm, Room 5417

**Roman Kossak**, CUNY

**The lattice problem for models of arithmetic**

The lattice problem for models of PA is to determine which lattices can be represented either as lattices of elementary substructures of a model of PA or, more generally, which can be represented as lattices of elementary substructures of a model N that contain a given elementary substructure M of N.

Since the 1970's, the problem generated much research with highly nontrivial results with proofs combining specific methods in the model theory of arithmetic with lattice theory and various combinatorial theorems. The problem has a definite answer in the case of distributive lattices, and, despite much effort, there are still many open questions in the nondistributive case. I will briefly survey some early results and present a few proofs that illustrate the difference between the distributive and nondistributive cases.

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - 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@citytech.cuny.edu.

If you have a logic-related event that you would like included in future mailings, please email

jreitz@citytech.cuny.edu.

## Cross-Alps Logic Seminar (speaker: Spencer Unger)

Cross-Alps Logic Seminar

4/29/2024 6:58:52

On Friday 03.05.2024 at 16.00 CEST

**Spencer Unger** (University of Toronto)

will give a talk on

*Iterated ultrapower methods*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 2022 'Models, Sets and Classifications'.

All the best,

Vincenzo

## This Week in Logic at CUNY

This Week in Logic at CUNY

4/28/2024 22:30:00

This Week in Logic at CUNY:

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Monday, Apr 29, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 29, 3:30pm Hill Center, Hill 705

Gabe Goldberg, Berkeley

Generalizations of the Ultrapower Axiom

Logic and Metaphysics Workshop

Date: Monday, April 29, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Anandi Hattiangadi (Stockholm).

Title: Physicalism, intentionality and normativity: The essential explanatory gap

Abstract: In this paper, I present an explanatory gap argument against the view that the semantic facts are fully grounded in the physical facts. Unlike traditional explanatory gap arguments, which stem from the failure of analytic reductive explanation, the explanatory gap I point to stems from the failure of metaphysical explanation. I argue for the following theses. (i) Physicalist grounding claims are metaphysically necessary, if true. (ii) To be explanatorily adequate, these grounding claims must be deducible from facts about essence. (iii) Semantico-physical grounding claims are possibly false, not (only) because they are conceivably false, but because they cannot be deduced from facts about essence. (iv) Semantic properties are essentially weakly normative: it lies in their natures to have correctness conditions and subjectively rationalize—rather than merely cause—behaviour. This gives rise to an explanatory gap that indicates that the semantic facts are not fully grounded in the physical facts.

- - - - Tuesday, Apr 30, 2024 - - - -

- - - - Wednesday, May 1, 2024 - - - -

- - - - Thursday, May 2, 2024 - - - -

- - - - Friday, May 3, 2024 - - - -

Model Theory Seminar

CUNY Graduate Center

Friday May 3, 12:30pm NY time, Room: 6495

Athar Abdul-Quader, Purchase College

Genericity in models of arithmetic

In this talk, I plan to explore a few notions of 'genericity' in the context of models of arithmetic. I will recall the notion of genericity borrowed from set-theory, used by Simpson to prove that every countable model of PA has an expansion to a pointwise definable model of PA*. I will then explore other notions of genericity inspired by more model-theoretic contexts. One such notion is 'neutrality': in a model M, we say an undefinable set X is neutral if the definable closure relation in (M, X) is the same as in M. Another notion, inspired by work done on model-theoretic genericity by Chatzidakis and Pillay, is called CP-genericity. I will explore these notions and outline some results, including: (1) every model of PA has a neutral set which is not CP-generic, (2) every countable model of PA has a CP-generic which is not neutral (and in fact, fails neutrality spectacularly: ie, we can find a CP-generic where the expansion is pointwise definable), and (3) every countable model of PA has a neutral CP-generic. This talk touches on work contained in two papers, one of which was joint work with Roman Kossak, and the other was joint work with James Schmerl.

Set Theory Seminar

CUNY Graduate Center

Friday, May 3, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

**Spencer Unger**, University of Toronto

**Iterated ultrapower methods in analysis of Prikry type forcing**

We survey some old and new results in singular cardinal combinatorics whose proofs can be phrased in terms of iterated ultrapowers and ask a few questions.

Logic Workshop

CUNY Graduate Center

Friday May 3, 2:00pm-3:30pm, Room 5417

**Christian Wolf**, CUNY

**Computability of entropy and pressure on compact symbolic spaces beyond finite type**

In this talk we discuss the computability of the entropy Htop(X) and topological pressure Ptop(ϕ) on compact shift spaces X and continuous potentials ϕ:X→R. This question has recently been studied for subshifts of finite type (SFTs) and their factors (Sofic shifts). We develop a framework to address the computability of the entropy pressure on general shift spaces and apply this framework to coded shifts. In particular, we prove the computability of the topological pressure for all continuous potentials on S-gap shifts, generalized gap shifts, and Beta shifts. We also construct shift spaces which, depending on the potential, exhibit computability and non-computability of the topological pressure. We further show that the generalized pressure function (X,ϕ)↦Ptop(X,ϕ|X) is not computable for a large set of shift spaces X and potentials ϕ. Along the way of developing these computability results, we derive several ergodic-theoretical properties of coded shifts which are of independent interest beyond the realm of computability. The topic of the talk is joint work with Michael Burr (Clemson U.), Shuddho Das (Texas Tech) and Yun Yang (Virginia Tech).

Next Week in Logic at CUNY:

- - - - Monday, May 6, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, May 6, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Lorenzo Rossi (Turin)

Title: Alethic pluralism and Kripkean truth

Abstract: According to alethic pluralism, there is more than one way of being true: truth is not unique, in that there is a plurality of truth properties each of which pertains to a specific domain of discourse. This paper shows how such a plurality can be represented in a coherent formal framework by means of a Kripke-style construction that yields intuitively correct extensions for distinct truth predicates. The theory of truth it develops can handle at least three crucial problems that have been raised in connection with alethic pluralism: mixed compounds, mixed inferences, and semantic paradoxes.

Note: This is joint work with Andrea Iacona (Turin) and Stefano Romeo (Turin).

- - - - Tuesday, May 7, 2024 - - - -

- - - - Wednesday, May 8, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: Juan Orendain, Case Western Univeristy.

Date and Time: Wednesday May 8, 2024, 7:00 - 8:30 PM. ZOOM TALK.

Title: Canonical squares in regularly framed bicategories.

- - - - Thursday, May 9, 2024 - - - -

- - - - Friday, May 10, 2024 - - - -

Logic Workshop

CUNY Graduate Center

Friday May 10, 2:00pm-3:30pm, Room 5417

**Roman Kossak**, CUNY

**The lattice problem for models of arithmetic**

The lattice problem for models of PA is to determine which lattices can be represented either as lattices of elementary substructures of a model of PA or, more generally, which can be represented as lattices of elementary substructures of a model N that contain a given elementary substructure M of N.

Since the 1970's, the problem generated much research with highly nontrivial results with proofs combining specific methods in the model theory of arithmetic with lattice theory and various combinatorial theorems. The problem has a definite answer in the case of distributive lattices, and, despite much effort, there are still many open questions in the nondistributive case. I will briefly survey some early results and present a few proofs that illustrate the difference between the distributive and nondistributive cases.

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - 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@citytech.cuny.edu.

If you have a logic-related event that you would like included in future mailings, please email

jreitz@citytech.cuny.edu.

## KGRC Set Theory Talk - May 2

Kurt Godel Research Center

4/26/2024 11:54:33

KGRC/Institute of Mathematics invites you to the following
Set Theory Seminar talk:
"Baumgartner's Axiom and Cardinal Characteristics: A Sparse Look at
Dense Sets of Reals II"
C. B. Switzer (U Wien)
Kolingasse 14–16, 1090, 1st floor, SR 10,
Thursday, May 2, 11:30am–1:00pm, hybrid mode
Mini-course (25.04.2024-16.05.2024, 3 lectures) - 2nd lecture:
Given a cardinal $\kappa$, a set of reals $A\subseteq \mathbb R$ is
$\kappa$-dense if its intersection with any open interval has size
$\kappa$. Baumgartner's axiom (BA)---proved consistent by Baumgartner
in 1973---states that all $\aleph_1$-dense sets of reals are order
isomorphic with the induced linear order from $\mathbb R$. This is the
most straightforward generalization to the uncountable of Cantor's proof
that all countable dense linear orders without endpoints are order
isomorphic. BA has variations to other topological spaces---given a
topological space $X$, a subset $A \subseteq X$ is $\kappa$-dense if its
intersection with each non-empty open subset has size $\kappa$. The
axiom BA($X$) states that given any two $\aleph_1$-dense subsets of
$X$, say $A$ and $B$, there is an autohomeomorphism of $X$ mapping
$A$ onto $B$. In this parlance BA is equivalent to BA ($\mathbb R$).
Surprisingly BA is not equivalent to BA ($\mathbb R^n$) for any finite
$1< n < \omega$. In fact BA does not follow from Martin's Axiom
(Abraham-Rubin-Shelah) though BA($\mathbb R^n$) does (in fact from
$\mathfrak{p} > \aleph_1$) for each $n > 1$ (Steprāns-Watson).
In these three lectures I will discuss these ideas and some related ones
including the question of when BA($X$) implies BA($Y$) for Polish
spaces $X$ and $Y$. Central to these questions are the role of cardinal
characteristics including the celebrated theorem of Todorčević that BA
implies $\mathfrak b > \aleph_1$ as well as a recent, higher dimensional
analogue of this result that for any $n < \omega$ BA($\mathbb R^n$)
implies $\mathfrak b > \aleph_1$ (S.-Steprāns). There are many beautiful
open problems in this area and I plan to make discussing them a focal
point of the talks. The talks will start slowly and should be accessible
to students. Time permitting, the final talk will include some new
results. If and when these results are presented, they are joint work
with Juris Steprāns.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Video recordings available so far of the Set Theory Seminar:
April, 25: C.B. Switzer (U Wien), "Baumgartner's Axiom and Cardinal
Characteristics: A Sparse Look at Dense Sets of Reals I".
https://ucloud.univie.ac.at/index.php/s/EoKqnND8XYdmyL6
Video recordings available so far of the Logic Colloquium:
April, 25: J. Lopez-Abad (UNED, Barcelona, ES), "Banach spaces as metric
model-theoretical structures".
https://ucloud.univie.ac.at/index.php/s/6G4MRfPMzBjYb8e
* * * * * * * * *
Updates at https://kgrc.univie.ac.at/eventsnews/.
--
Institute of Mathematics (Kurt Goedel Research Center, Logic)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## Wednesday seminar

Prague Set Theory Seminar

4/26/2024 6:10:45

Dear all,
There will be no Wednesday seminar the following two weeks, May 1st and
May 8th (public holidays). The seminar should resume on Wednesday May
15th, Jonathan Cancino Manriquez will be presenting his results on
basically generated and Tukey-top ultrafilters.
Sean Cox will be visiting Prague starting next week, he will give
seminar talks on Monday May 6th at the Algebra seminar in Karlin
https://www.mff.cuni.cz/cs/math/ka/akce/seminare/algebraicky-seminar
and on Tuesday May 7th at the Set Theory and Analysis seminar in the
Institute
https://www.math.cas.cz/index.php/events/event/3764
Best,
David

## 51st Nankai Logic Colloquium

Nankai Logic Colloquium

4/25/2024 10:03:15

Hello everyone,

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

Our speaker this week will be Jiachen Yuan from the University of Leeds. This talk is going to take place this Friday, Apr 26, from 4pm to 5pm(UTC+8, Beijing time).

Title: What happens at the limit of a sequence of models of ZFC

Abstract: The technique of taking the tail model is an understudied object in the study of Mathematical logic. With Assaf Rinot and Zhixing You, we find it is a useful tool for constructing interesting ultrafilters. In this talk, I'll illustrate how we use it to answer a question about $\delta$-complete ultrafilters and to extend some results in infinitary combinatorics.

___________________________________________________________________________________________________________________________________________________

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 51st Nankai Logic Colloquium -- Jiachen Yuan

Time ：16:00pm, Apr. 26, 2024(Beijing Time)

Zoom Number ： 734 242 5443

Passcode ：477893

Link ：https://zoom.us/j/7342425443?pwd=NnO2EFts9VOfCR9eDFUkoI3lNn2QTo.1&omn=84627872662

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

4/22/2024 11:47:18

Hi everyone,

CUNY is on Spring Break through April 30th - however, there are still some logic events happening in and around New York City, at CUNY and beyond.

Hope all is well,

Jonas

This Week in Logic at CUNY:

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Monday, Apr 22, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 22, 3:30pm Hill Center, Hill 705

Dave Marker, University of Illinois at Chicago

Rigid real closed fields

- - - - Tuesday, Apr 23, 2024 - - - -

Computational Logic Seminar

Spring 2024 (online)

Tuesday, April 23, Time 2:00 - 4:00 PM (EDT)

zoom link: ask Sergei Artemov (

sartemov@gmail.com)

Speaker: Thomas Schlögl, Technische Universität Wien

Title: Epistemic Modeling of Truly Private Updates and a Glance at

a New Epistemic Model Checking and Visualization Tool

Abstract: Epistemic logic has been successfully applied to the modeling of epistemic and doxastic attitudes of agents in distributed systems. Dynamic Epistemic Logic (DEL) adds communication via model transforming updates. Since agents in distributed systems often exchange information without other agents knowing, however, the commonly known model updates in DEL are generally not adequate for describing fully private communication. In this talk, I will present a novel update mechanism for solving the fully private consistent update synthesis task: designing a model update that makes a given goal formula true while maintaining the consistency of the agents’ beliefs.

In addition, I will provide a first glimpse of the alpha version of a performant epistemic model checking and visualization tool I am currently working on. Model-checking allows us to verify whether a finite-state model (typically represented as a Kripke structure) satisfies a given specification. Many model-checking tools exist for a variety of logical languages, including epistemic logic. To effectively support foundational theoretical research like developing sound and efficient fully private model updates, however, a tool is needed that simultaneously provides:

.) a flexible and intuitive user interface,

.) powerful visualization capabilities for large models (>10,000 states),

.) a performant model-checking algorithm that also provides explanations/proofs/counter-examples

.) easy extendability w.r.t. logical language features and model generation/updates

- - - - Wednesday, Apr 24, 2024 - - - -

- - - - Thursday, Apr 25, 2024 - - - -

- - - - Friday, Apr 26, 2024 - - - -

Next Week in Logic at CUNY:

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Monday, Apr 29, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, April 29, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Anandi Hattiangadi (Stockholm).

Title: Physicalism, intentionality and normativity: The essential explanatory gap

Abstract: In this paper, I present an explanatory gap argument against the view that the semantic facts are fully grounded in the physical facts. Unlike traditional explanatory gap arguments, which stem from the failure of analytic reductive explanation, the explanatory gap I point to stems from the failure of metaphysical explanation. I argue for the following theses. (i) Physicalist grounding claims are metaphysically necessary, if true. (ii) To be explanatorily adequate, these grounding claims must be deducible from facts about essence. (iii) Semantico-physical grounding claims are possibly false, not (only) because they are conceivably false, but because they cannot be deduced from facts about essence. (iv) Semantic properties are essentially weakly normative: it lies in their natures to have correctness conditions and subjectively rationalize—rather than merely cause—behaviour. This gives rise to an explanatory gap that indicates that the semantic facts are not fully grounded in the physical facts.

- - - - Tuesday, Apr 30, 2024 - - - -

- - - - Wednesday, May 1, 2024 - - - -

- - - - Thursday, May 2, 2024 - - - -

- - - - Friday, May 3, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, May 3, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

**Spencer Unger**, University of Toronto

**Iterated ultrapower methods in analysis of Prikry type forcing**

We survey some old and new results in singular cardinal combinatorics whose proofs can be phrased in terms of iterated ultrapowers and ask a few questions.

Logic Workshop

CUNY Graduate Center

Friday May 3, 2:00pm-3:30pm, Room 5417

**Christian Wolf**, CUNY

**Computability of entropy and pressure on compact symbolic spaces beyond finite type**

In this talk we discuss the computability of the entropy Htop(X) and topological pressure Ptop(ϕ) on compact shift spaces X and continuous potentials ϕ:X→R. This question has recently been studied for subshifts of finite type (SFTs) and their factors (Sofic shifts). We develop a framework to address the computability of the entropy pressure on general shift spaces and apply this framework to coded shifts. In particular, we prove the computability of the topological pressure for all continuous potentials on S-gap shifts, generalized gap shifts, and Beta shifts. We also construct shift spaces which, depending on the potential, exhibit computability and non-computability of the topological pressure. We further show that the generalized pressure function (X,ϕ)↦Ptop(X,ϕ|X) is not computable for a large set of shift spaces X and potentials ϕ. Along the way of developing these computability results, we derive several ergodic-theoretical properties of coded shifts which are of independent interest beyond the realm of computability. The topic of the talk is joint work with Michael Burr (Clemson U.), Shuddho Das (Texas Tech) and Yun Yang (Virginia Tech).

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - 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@citytech.cuny.edu.

If you have a logic-related event that you would like included in future mailings, please email

jreitz@citytech.cuny.edu.

## Wednesday seminar

Prague Set Theory Seminar

4/21/2024 14:54:11

Dear all,
The seminar meets on Wednesday April 24th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jonathan has some major results and he will give a couple of
talks on these new things.
Jonathan Cancino Manriquez -- Introduction to Tukey types of
ultrafilters on the natural numbers
This will be an introductory talk to the Tukey types of ultrafilters on
the natural numbers. We will review some of the classical facts related
to Tukey top ultrafilters and basically generated ultrafilters. The
talks will be mostly based on the papers "Tukey classes of ultrafilters
on ω" (D. Millovich), and "Tukey types of ultrafilters" (N. Dobrinen and
S. Todorcevic).
Best,
David

## Set theory and topology seminar 23.04.2024 Tomasz Żuchowski

Wrocław Set Theory Seminar

4/21/2024 8:38:30

I am happy to announce that at the seminar in set theory and topology (on Tuesday 23.04.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"The Nikodym property and filters on $\omega$. Part II"

**Tomasz Żuchowski**

Abstract:

In this talk we will continue studying the family $\mathcal{AN}$ of ideals on $\omega$ presented in the Part I. Recall that $\mathcal{I}\in\mathcal{AN}$ iff there exists a density submeasure $\varphi$ on $\omega$ such that $\varphi(\omega)=\infty$ and $\mathcal{I}\subseteq Exh(\varphi)$.

We will present several conditions for a density ideal $\mathcal{I}$ equivalent to the fact that $\mathcal{I}\in\mathcal{AN}$. Next, we will make an analysis of the cofinal structure of the family $\mathcal{AN}$ ordered by the Katetov order $\leq_K$. We will prove that there is a family of size $\mathfrak{d}$ which is $\leq_K$-dominating in $\mathcal{AN}$, but there are no $\leq_K$-maximal elements in $\mathcal{AN}$.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## KGRC Talks - April 25

Kurt Godel Research Center

4/19/2024 11:03:26

KGRC/Institute of Mathematics invites you to the following talks:
Set Theory Seminar
Kolingasse 14--16, 1090, 1st floor, SR 10,
Thursday, April 25, 11:30am--1:00pm, hybrid mode
"Baumgartner's Axiom and Cardinal Characteristics: A Sparse Look at
Dense Sets of Reals"
C. B. Switzer (U Wien)
Mini-course (25.04.2024-16.05.2024, 3 lectures) - 1st lecture:
Given a cardinal $\kappa$, a set of reals $A\subseteq \mathbb R$ is
$\kappa$-dense if its intersection with any open interval has size
$\kappa$. Baumgartner's axiom (BA)---proved consistent by Baumgartner in
1973---states that all $\aleph_1$-dense sets of reals are order
isomorphic with the induced linear order from $\mathbb R$. This is the
most straightforward generalization to the uncountable of Cantor's proof
that all countable dense linear orders without endpoints are order
isomorphic. BA has variations to other topological spaces---given a
topological space $X$, a subset $A \subseteq X$ is $\kappa$-dense if its
intersection with each non-empty open subset has size $\kappa$. The
axiom BA($X$) states that given any two $\aleph_1$-dense subsets of $X$,
say $A$ and $B$, there is an autohomeomorphism of $X$ mapping $A$ onto
$B$. In this parlance BA is equivalent to BA ($\mathbb R$). Surprisingly
BA is not equivalent to BA ($\mathbb R^n$) for any finite $1< n <
\omega$. In fact BA does not follow from Martin's Axiom
(Abraham-Rubin-Shelah) though BA($\mathbb R^n$) does (in fact from
$\mathfrak{p} > \aleph_1$) for each $n > 1$ (Steprāns-Watson).
In these three lectures I will discuss these ideas and some related ones
including the question of when BA($X$) implies BA($Y$) for Polish spaces
$X$ and $Y$. Central to these questions are the role of cardinal
characteristics including the celebrated theorem of Todorčević that BA
implies $\mathfrak b > \aleph_1$ as well as a recent, higher dimensional
analogue of this result that for any $n < \omega$ BA($\mathbb R^n$)
implies $\mathfrak b > \aleph_1$ (S.-Steprāns). There are many beautiful
open problems in this area and I plan to make discussing them a focal
point of the talks. The talks will start slowly and should be accessible
to students. Time permitting, the final talk will include some new
results. If and when these results are presented, they are joint work
with Juris Steprāns.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Logic Colloquium
Oskar-Morgenstern-Platz 1, 1090, 2nd floor, HS 11,
Thursday, April 25, 3:00pm--3:50pm, hybrid mode
"Banach spaces as metric model-theoretical structures"
J. López Abad, UNED, Barcelona, ES
Banach spaces are a reach family of metric model structures. We will
discuss this in particular focussing on omega-categoricity,
ultrahomogeneity and extreme amenability, where also combinatorics plays
a crucial role.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at
Please direct any questions about this talk to
matthias.aschenbrenner@univie.ac.at.
* * * * * * * * *
Video recordings available so far of the Set Theory Seminar:
April, 18: R. Sullivan (U Münser, DE), "Generic embeddings into Fraïssé
structures":
https://ucloud.univie.ac.at/index.php/s/riHYm5qikdkPCws
Video recordings available so far of the Logic Colloquium:
April, 18: C. Agostini (TU Wien), "Countable spaces and realcompactness":
https://ucloud.univie.ac.at/index.php/s/6Az7PQPE5x8aEEy
* * * * * * * * *
Updates at https://kgrc.univie.ac.at/eventsnews/

## 50th Nankai Logic Colloquium

Nankai Logic Colloquium

4/18/2024 13:32:46

Hello everyone,

This week our weekly Nankai Logic Colloquium is going to be in the afternoon, but at an irregular time, as we have two speakers this week.

Our speakers this week will be Stevo Todorcevic from the University of Toronto and Dilip Raghavan from the National University of Singapore. This talk is going to take place this Friday, April 19, from 2:30 pm to 5 pm (UTC+8, Beijing time). The first talk is offline/online hybrid starting at 2:30pm, and the second talk is online starting at 4pm.

Stevo Todorcevic:

Title: Ultrafilters in L(R)[U]

Abstract: We give analysis of the inner model L(R)[U] under the assumptions that L(R) is a Solovay model and U is a selective ultrafilter on N. A survey of known results and open problems will be given.

Dilip Raghavan:

Title: Stable ordered-union ultrafilters

Abstract: Stable ordered-union ultrafilters were introduced by Blass in 1987. They stand in the same relation to the Milliken-Taylor theorem as selective ultrafilters do to Ramsey's theorem. In this talk, I will survey some results and problems about stable ordered-union ultrafilters.

___________________________________________________________________________________________________________________________________________________

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 50th Nankai Logic Colloquium

Time（Stevo Todorcevic） ：14:30pm, Apr. 19, 2024(Beijing Time)

Time（Dilip Raghavan） ：16:00pm, Apr. 19, 2024(Beijing Time)

Zoom Number ： 734 242 5443

Passcode ：477893

Link ：https://zoom.us/j/7342425443?pwd=NnO2EFts9VOfCR9eDFUkoI3lNn2QTo.1&omn=81450804954

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

4/14/2024 22:28:00

This Week in Logic at CUNY:

- - - - Monday, Apr 15, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 15, 3:30pm Hill Center, Hill 705

Mark Poor, Cornell

Shelah groups in ZFC

Logic and Metaphysics Workshop

Date: Monday, April 15, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Jessica Collins (Columbia)

Title: Imaging is Alpha + Aizerman

Abstract: I give a non-probabilistic account of the imaging revision process. Most familiar in its various probabilistic forms, imaging was introduced by David Lewis (1976) as the form of belief revision appropriate for supposing subjunctively that a hypothesis be true. It has played a central role in the semantics of subjunctive conditionals, in causal decision theory, and, less well known to philosophers, in the computational theory of information retrieval. In the economics literature, non-probabilistic imaging functions have been called “pseudo-rationalizable choice functions”. I show that the imaging functions are precisely those which satisfy both Sen’s Alpha Principle (aka “Chernoff’s Axiom”) and the Aizerman Axiom. This result allows us to see very clearly the formal relationship between non-probabilistic imaging and AGM revision (which is Alpha + Beta).

- - - - Tuesday, Apr 16, 2024 - - - -

Computational Logic Seminar

Spring 2024 (online)

Tuesday, April 16, Time 2:00 - 4:00 PM

zoom link: contact Sergei Artemov (

sartemov@gmail.com)

Speaker: Lukas Zenger, University of Bern

Title: Intuitionistic modal logic with the master modality

Abstract: I present a cyclic sequent calculus for intuitionistic modal logic with the master modality. Formulas of the logic are evaluated over bi-relational Kripke models with three different frame conditions: functional frames, `triangle' confluent frames, and arbitrary frames. It is shown that the calculus is sound and complete for all three classes of models. This, in particular, proves that intuitionistic modal logic with the master modality cannot distinguish between arbitrary models and functional models. Soundness is established by a standard argument while completeness is proven via a detour to non-wellfounded proofs, using a proof-search argument that draws on analyticity of the calculus. The framework is robust in the sense that it can be naturally adapted to account for various frame conditions, such as serial models, reflexive models or S4-models, as well as for a polymodal extension that can be interpreted as intuitionistic common knowledge. This is joint work with Lide Grotenhuis, Bahareh Afshari and Graham Leigh.

- - - - Wednesday, Apr 17, 2024 - - - -

- - - - Thursday, Apr 18, 2024 - - - -

- - - - Friday, Apr 19, 2024 - - - -

Logic Workshop

CUNY Graduate Center

Friday April 19, 2:00pm-3:30pm, Room 5417

Philip Scowcroft, Wesleyan University

Some applications of model theory to lattice-ordered groups

When does a hyperarchimedean lattice-ordered group embed into a hyperarchimedean lattice-ordered group with strong unit? After explaining the meaning of this question, I will describe some partial answers obtained via model theory.

Next Week in Logic at CUNY:

- - - - Monday, Apr 22, 2024 - - - -

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Tuesday, Apr 23, 2024 - - - -

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Wednesday, Apr 24, 2024 - - - -

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Thursday, Apr 25, 2024 - - - -

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Friday, Apr 26, 2024 - - - -

*** CUNY SPRING RECESS APRIL 22 - 30 ***

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - Web Site - - - -

Find us on the web at:

nylogic.github.io(site designed, built & maintained by Victoria Gitman)

-------- ADMINISTRIVIA --------

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If you have a logic-related event that you would like included in future mailings, please email

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## KGRC Talks - April 18

Kurt Godel Research Center

4/12/2024 3:31:22

KGRC/Institute of Mathematics invites you to the following talks:
Set Theory Seminar
Kolingasse 14–16, 1090, 1st floor, SR 10,
Thursday, April 18, 11:30am–1:00pm, hybrid mode
"Generic embeddings into Fraïssé structures"
R. Sullivan (U Münster, DE)
This project, in the writing-up stage, is work with A. Codenotti
(Münster), A. Panagiotopoulos (Vienna) and J. Winkel.
Let M be a Fraïssé structure (eg the random graph), and let A be a
countably infinite structure which is embeddable in M. If M has free
amalgamation, then there exists a Katetov embedding of A into M: an
embedding such that each automorphism of A extends to an automorphism of
M. Is this embedding "common" or "uncommon"?
To answer this, we investigate generic embeddings of A into M. An
embedding of A into M is said to be generic if it lies in a comeagre set
inside the Polish space Emb(A, M).
We will answer the following three questions:
- When are two embeddings of A into M generically isomorphic via an
automorphism of M?
- When is A generically corigid (i.e. Aut(M/A) trivial)?
- Let g lie in Aut(A). When is g generically extensible to an
automorphism of M?
We will also discuss a wide range of examples in the context of these
three questions.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact richard.springer@univie.ac.at.
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Logic Colloquium
Oskar-Morgenstern-Platz 1, 1090, 2nd floor, HS 11,
Thursday, April 18, 3:00pm--3:50pm, hybrid mode
"Countable spaces and realcompactness"
C. Agostini (TU Wien)
In this talk, we analyze the realcompactness number of countable spaces.
We will show that, for every cardinal $\kappa$, there exists a countable
crowded space $X$ such that $\mathsf{Exp}(X)=\kappa$ if and only if
$\mathfrak{p}\leq\kappa\leq\mathfrak{c}$. On the other hand, we show
that a scattered space of weight $\kappa$ has pseudocharacter at most
$\kappa$ in any compactification. will allow us to calculate
$\mathsf{Exp}(X)$ for an arbitrary (that is, not necessarily crowded)
countable space.
This is a joint work with Andrea Medini and Lyubomyr Zdomskyy.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact richard.springer@univie.ac.at.
Please direct any questions about this talk to
matthias.aschenbrenner@univie.ac.at.
* * * * * * * * *
Video recordings available so far of the Set Theory Seminar:
April, 11: J. M. Millhouse (U Wien), "Definable well-orderings of a
large continuum".
https://ucloud.univie.ac.at/index.php/s/twWpnZPHd8DscTe
Updates at https://kgrc.univie.ac.at/eventsnews/
--
Mag. Petra Czarnecki de Czarnce-Chalupa
Institute of Mathematics (Kurt Goedel Research Center, Logic)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## Set theory and toplogy seminar 16.04.2024 Krzysztof Zakrzewski (UW)

Wrocław Set Theory Seminar

4/11/2024 4:46:45

I am happy to announce that at the seminar in set theory and topology (on Tuesday 16.04.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"Function spaces on Corson-like compacta"

**Krzysztof Zakrzewski (MIM UW)**

Abstract:

Recall that a compact space is Eberlein compact if it is homeomorphic to a subspace of some Banach space equipped with the weak topology. A compact space is \omega-Corson compact if it embeds into a \sigma-product of real lines, that is a subspace of the product R^{\Gamma} consisting of sequences with finitely many nonzero coordinates for some set \Gamma.

Every \omega-Corson compact space is Eberlein compact. For a Tichonoff space X, let Cp(X) denote the space of real continuous functions on X endowed with the pointwise convergence topology.

During the talk we will show that the class \omega-Corson compact spaces K is invariant under linear homeomorphism of function spaces Cp(K) and other related results.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

## Wednesday seminar

Prague Set Theory Seminar

4/9/2024 10:53:14

Dear all,
There will be no seminar tomorrow, Wednesday April 10th due to the
expected lack of speakers. (Apologies for the late notice.)
The seminar will again next week, Wednesday April 17th at 11:00 in the
Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front
building.
Program: Ziemowit Kostana -- Diamond on Kurepa trees
I will discuss a restricted variant of Jensen's Diamond, that is
guessing only cofinal branches of a given Kurepa tree. It turns out to
be a very weak guessing principle, in particular
does not imply CH, and follows from Club. Nevertheless, this weak
variant may still consistently fail. This is joint work with Assaf Rinot
and Saharon Shelah.
Best,
David

## Two Related Seminars in Geometry and Topology by Shlpak Banerjee and in Logic by Philipp Kunde on Wednesday 17 April 2024

NUS Logic Seminar

4/8/2024 5:49:31

On 17 April 2024 there will be two related lectures in two seminar
series at the NUS.
At 15:30 hrs, Dr. Shilpak Banerjee will give talk at Geometry&Topology
seminar with title "(Anti-)classification results in Dynamical Systems
and Ergodic Theory" in S17-05-12, (Abstract_talk1).
At 17:00 hrs, Dr. Philipp Kunde will present
at logic seminar in S17-04-05 with title
Non-classifiability of ergodic flows up to
time change, (Abstract_talk2).
Best regards, Frank and Yue for Logic Seminar, Daren for Geometry
and Topology Seminar; all of us at Department of Mathematics, NUS.

## This Week in Logic at CUNY

This Week in Logic at CUNY

4/7/2024 22:50:00

This Week in Logic at CUNY:

- - - - Monday, Apr 8, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 8, Hill Center, Hill 705, SPECIAL TIME: 4:00pm

Jing Zhang, Toronto

Squares, ultrafilters and forcing axioms

Logic and Metaphysics Workshop

Date: Monday, April 8, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Asya Passinsky (CEU)

Title: Social construction and meta-ground

Abstract: The notion of social construction plays an important role in many areas of social philosophy, including the philosophy of gender, the philosophy of race, and social ontology. But it is far from clear how this notion (or cluster of notions) is to be understood. One promising proposal, which has been championed in recent years by Aaron Griffith (2017, 2018) and Jonathan Schaffer (2017), is that the notion of constitutive social construction may be analyzed in terms of the notion of metaphysical grounding. In this paper, I argue that a simple ground-theoretic analysis of social construction is subject to two sorts of problem cases and that existing ground-theoretic accounts do not avoid these problems. I then develop a novel ground-theoretic account of social construction in terms of meta-ground, and I argue that it avoids the problems. The core idea of the account is that in cases of social construction, the meta-ground of the relevant grounding fact includes a suitable connective social fact.

- - - - Tuesday, Apr 9, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Virtual (email Victoria Gitman for meeting id)

Tuesday, April 9, 1pm

Athar Abdul-Quader, Purchase College

Representations of lattices

Following up on the series of talks on the history of the problem, in this talk we will discuss the main technique for realizing finite lattices as interstructure lattices, due to Schmerl in 1986. We will motivate this technique by studying an example: the Boolean algebra B2. We will see how we can modify the technique to produce elementary extensions realizing specific ranked lattices to ensure that such extensions are end, cofinal, or mixed extensions.

- - - - Wednesday, Apr 10, 2024 - - - -

Speaker: Ellis D. Cooper.

Date and Time: Wednesday April 10, 2024, 7:00 - 8:30 PM. IN-PERSON

Title: Pulse Diagrams and Category Theory.

Abstract: ``Pulse diagrams'' are motivated by the ubiquity of pulsation in biology, from action potentials, to heartbeat, to respiration, and at longer time-scales to circadian rhythms and even to human behavior. The syntax of the diagrams is simple, and the semantics are easy to define and simulate with Python code. They express behaviors of parts and wholes as in categorical mereology, but are missing a compositional framework, like string diagrams. Examples to discuss include cellular automata, leaky-integrate-and-fire neurons, harmonic frequency generation, Gillespie algorithm for the chemical master equation, piecewise-linear genetic regulatory networks, Lotka-Volterra systems, and if time permits, aspects of the adaptive immune system. The talk is more about questions than about answers.

- - - - Thursday, Apr 11, 2024 - - - -

- - - - Friday, Apr 12, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, April 12, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Boban Velickovic University of Paris

Logic Workshop

CUNY Graduate Center

Friday April 12, 2:00pm-3:30pm, Room 5417

**Hans Schoutens**, CUNY

**Geometric tools for the decidability of the existential theory of Fp[[t]]**

I will give a brief survey how tools from algebraic geometry can be used in finding solutions to Diophantine equations over Fp[[t]] and similar rings. These tools include Artin approximation, arc spaces, motives and resolution of singularities. This approach yields the definability of the existential theory of Fp[[t]] (in the ring language with a constant for t) contingent upon the validity of resolution of singularities (Denef-Schoutens). Anscombe-Fehm proved a weaker result using model-theoretic tools and together with Dittmann, they gave a proof assuming only the weaker 'local uniformization conjecture.'

Next Week in Logic at CUNY:

- - - - Monday, Apr 15, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 15, 3:30pm Hill Center, Hill 705

Mark Poor, Cornell

Logic and Metaphysics Workshop

Date: Monday, April 15, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Jessica Collins (Columbia)

Title: Imaging is Alpha + Aizerman

Abstract: I give a non-probabilistic account of the imaging revision process. Most familiar in its various probabilistic forms, imaging was introduced by David Lewis (1976) as the form of belief revision appropriate for supposing subjunctively that a hypothesis be true. It has played a central role in the semantics of subjunctive conditionals, in causal decision theory, and, less well known to philosophers, in the computational theory of information retrieval. In the economics literature, non-probabilistic imaging functions have been called “pseudo-rationalizable choice functions”. I show that the imaging functions are precisely those which satisfy both Sen’s Alpha Principle (aka “Chernoff’s Axiom”) and the Aizerman Axiom. This result allows us to see very clearly the formal relationship between non-probabilistic imaging and AGM revision (which is Alpha + Beta).

- - - - Tuesday, Apr 16, 2024 - - - -

- - - - Wednesday, Apr 17, 2024 - - - -

- - - - Thursday, Apr 18, 2024 - - - -

- - - - Friday, Apr 19, 2024 - - - -

Logic Workshop

CUNY Graduate Center

Friday April 19, 2:00pm-3:30pm, Room 5417

Philip Scowcroft, Wesleyan University

Some applications of model theory to lattice-ordered groups

When does a hyperarchimedean lattice-ordered group embed into a hyperarchimedean lattice-ordered group with strong unit? After explaining the meaning of this question, I will describe some partial answers obtained via model theory.

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

## Logic Seminar Tuesday 9 April 2023 by Piotr Kowalski

NUS Logic Seminar

4/5/2024 5:03:32

Invitation to the Logic Seminar at the National University of Singapore
Date: Tuesday, 9 April 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#05-11
Speaker: Piotr Kowalski
Title: Model Completeness and Matrix Groups
Abstract:
I plan to discuss the notions of model companion and model
completeness focusing on algebraic and geometric examples.
For instance, I will mention recent joint work with Daniel
Max Hoffmann, Chieu-Minh Tran and Jinhe Ye, where we consider
model completeness of certain matrix groups.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## KGRC Talk - April 11

Kurt Godel Research Center

4/4/2024 11:13:47

KGRC/Institute of Mathematics invites you to the following
Set Theory Seminar talk:
”Definable well-orderings of a large continuum”
J. M. Millhouse (U Wien)
Kolingasse 14–16, 1090, 1st floor, SR 10,
Thursday, April 11, 11:30am–1:00pm, hybrid mode
This is the first in a series of talks where I will be going over the
history and the more recent advancements in forcing techniques used to
produce models of set theory where the continuum is strictly greater
than \(\aleph_1\), a projective well-order of the reals.
In the first talk we will establish preliminaries, understand the
motivation for obtaining such models, and go over L. Harrington's
initial 1977 construction. Subsequent talks will focus on some more
recent results, including applications of the techniques to the theory
of cardinal characteristics and the definability of various
combinatorial sets of reals.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at.
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Video recordings available so far of the Set Theory Seminar:
March, 21: M. Iannela (TU Wien), "(Piecewise) convex embeddability on
linear orders"
https://ucloud.univie.ac.at/index.php/s/eMc25cWsJzswFAx
* * * * * * * * *
Updates at https://kgrc.univie.ac.at/eventsnews/
--
Mag. Petra Czarnecki de Czarnce-Chalupa
Institute of Mathematics (Kurt Goedel Research Center, Logic)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## Nankai Logic Colloquium paused for two weeks

Nankai Logic Colloquium

4/4/2024 10:47:48

Hello Everyone,

Our Nankai Logic Colloquium is going to pause for these two weeks (April 5th and April 12th) for The 4th International Conference on Topological Algebras and Their Applications, which is currently being held at Nankai University.

The Nankai Logic Colloquium is going to be resumed after two weeks (April 19th). On that day we are going to have two talks: one given by Stevo Todorcevic and one given by Dilip Raghavan.

See you online in two weeks!

Best wishes,

Ming Xiao

## Set theory and topology seminar 9.04.2024 Jakub Rondos

Wrocław Set Theory Seminar

4/4/2024 5:07:52

I am happy to announce that at the seminar in set theory and topology (on Tuesday 9.04.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"Topological properties of compact spaces K that are preserved by isomorphisms of C(K)"

**Jakub Rondos (University of Vienna)**

Abstract:

In the talk, we present some newly discovered properties of compact Hausdorff spaces that are preserved by isomorphisms of their Banach spaces of continuous functions.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## Cross-Alps Logic Seminar (speaker: Luca Motto Ros)

Cross-Alps Logic Seminar

4/2/2024 7:02:01

On Friday 05.04.2024 at 16.00 CEST

**Luca Motto Ros** (University of Torino)

will give a talk on

*Borel complexity of graph homomorphism*

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 2022 'Models, Sets and Classifications'.

All the best,

Vincenzo

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/31/2024 22:42:00

This Week in Logic at CUNY:

- - - - Monday, Apr 1, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, April 1, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Andrew Tedder (Vienna).

Title: Relevant logics as topical logics

Abstract: There is a simple way of reading a structure of topics into the matrix models of a given logic, namely by taking the topics of a given matrix model to be represented by subalgebras of the algebra reduct of the matrix, and then considering assignments of subalgebras to formulas. The resulting topic-enriched matrix models bear suggestive similarities to the two-component frame models developed by Berto et. al. in Topics of Thought. In this talk I’ll show how this reading of topics can be applied to the relevant logic R, and its algebraic characterisation in terms of De Morgan monoids, and indicate how we can, using this machinery and the fact that R satisfies the variable sharing property, read R as a topic-sensitive logic. I’ll then suggest how this approach to modeling topics can be applied to a broader range of logics/classes of matrices, and gesture at some avenues of research.

- - - - Tuesday, Apr 2, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Virtual (email Victoria Gitman for meeting id)

Tuesday, April 2, 1pm

**Athar Abdul-Quader**, Purchase College

**Representations of lattices**

Following up on the series of talks on the history of the problem, in this talk we will discuss the main technique for realizing finite lattices as interstructure lattices, due to Schmerl in 1986. We will motivate this technique by studying an example: the Boolean algebra B2. We will see how we can modify the technique to produce elementary extensions realizing specific ranked lattices to ensure that such extensions are end, cofinal, or mixed extensions.

**Computational Logic Seminar **

**Spring 2024 ****(online) **

**Tuesday, April 2, ****Time 2:00 - 4:00 PM **

**Speaker: ****Sonja J.L. Smets**, The University of Amsterdam** **

**Title:** *Reasoning about Epistemic Superiority and Data Exchange***Abstract: **In this presentation I focus on a framework that generalizes dynamic epistemic logic in order to model a wider range of scenarios including those in which agents read or communicate (or somehow gain access to) all the information stored at specific sources, or possessed by some other agents (including information of a non-propositional nature, such as data, passwords, secrets etc). The resulting framework allows one to reason about the state of affairs in which one agent (or group of agents) has ‘epistemic superiority’ over another agent (or group). I will present different examples of epistemic superiority and I will draw a connection to the logic of functional dependence by A. Baltag and J. van Benthem. At the level of group attitudes, I will further introduce the new concept of 'common distributed knowledge', which combines features of both common knowledge and distributed knowledge. This presentation is based on joint work with A. Baltag in [1].

[1] A. Baltag and S. Smets, Learning what others know, in L. Kovacs and E. Albert (eds.), LPAR23 proceedings of the International Conference on Logic for Programming, AI and Reasoning, EPiC Series in Computing, 73:90-110, 2020. https://doi.org/10.29007/plm4

- - - - Wednesday, Apr 3, 2024 - - - -

- - - - Thursday, Apr 4, 2024 - - - -

- - - - Friday, Apr 5, 2024 - - - -

Philog Seminar

The Graduate Center of The City University of New York

April 5, Friday, 10 AM

Zoom meeting, please contact

Rohit Parikh for zoom link

Gilberto Gomes, Northern Rio de Janeiro State University

The Implicative Conditional

This talk will present and discuss the paper *The implicative conditional*, by Eric Raidl and myself, recently published in *Journal of Philosophical Logic* (with free access). The paper presents a proposal for a strong conditional, that is, one that really expresses that the consequent is a consequence of the antecedent, or that the antecedent is a sufficient reason for believing the consequent, in a given context. We claim that the implicative conditional describes the logical behavior of an empirically defined class of natural language conditionals, also named implicative conditionals, which excludes concessive and some other conditionals. The logical properties of this conditional in a reflexive normal Kripke semantics will be discussed. Its axiomatic system, which was proved sound and complete, will be presented. The implicative conditional avoids the paradoxes of the material and strict conditionals, presents connexive properties, and assures the relevance of the antecedent to the consequent.

Set Theory Seminar

CUNY Graduate Center

Friday, April 5, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Kameryn Williams Bard College at Simon's Rock

Logic Workshop

CUNY Graduate Center

Friday April 5, 2:00pm-3:30pm, Room 5417

Meng-Che 'Turbo' Ho, California State University at Northridge

Decision problem for groups as equivalence relations

In 1911, Dehn proposed three decision problems for finitely presented groups: the word problem, the conjugacy problem, and the isomorphism problem. These problems have been central to both group theory and logic, and were each proven to be undecidable in the 50's. There is much current research studying the decidability of these problems in certain classes of groups.

Classically, when a decision problem is undecidable, its complexity is measured using Turing reducibility. However, Dehn's problems can also be naturally thought of as computably enumerable equivalence relations (ceers). We take this point of view and measure their complexity using computable reductions. This yields behaviors different from the classical context: for instance, every Turing degree contains a word problem, but not every ceer degree does. This leads us to study the structure of ceer degrees containing a word problem and other related questions.

Next Week in Logic at CUNY:

- - - - Monday, Apr 8, 2024 - - - -

Rutgers Logic Seminar

Monday Apr 8, 3:30pm, Hill Center, Hill 705

Jing Zhang

Logic and Metaphysics Workshop

Date: Monday, April 8, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Asya Passinsky (CEU)

Title: Social construction and meta-ground

Abstract: The notion of social construction plays an important role in many areas of social philosophy, including the philosophy of gender, the philosophy of race, and social ontology. But it is far from clear how this notion (or cluster of notions) is to be understood. One promising proposal, which has been championed in recent years by Aaron Griffith (2017, 2018) and Jonathan Schaffer (2017), is that the notion of constitutive social construction may be analyzed in terms of the notion of metaphysical grounding. In this paper, I argue that a simple ground-theoretic analysis of social construction is subject to two sorts of problem cases and that existing ground-theoretic accounts do not avoid these problems. I then develop a novel ground-theoretic account of social construction in terms of meta-ground, and I argue that it avoids the problems. The core idea of the account is that in cases of social construction, the meta-ground of the relevant grounding fact includes a suitable connective social fact.

- - - - Tuesday, Apr 9, 2024 - - - -

- - - - Wednesday, Apr 10, 2024 - - - -

- - - - Thursday, Apr 11, 2024 - - - -

- - - - Friday, Apr 12, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, April 12, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Boban Velickovic University of Paris

Logic Workshop

CUNY Graduate Center

Friday April 12, 2:00pm-3:30pm, Room 5417

**Hans Schoutens**, CUNY

**Geometric tools for the decidability of the existential theory of Fp[[t]]**

I will give a brief survey how tools from algebraic geometry can be used in finding solutions to Diophantine equations over Fp[[t]] and similar rings. These tools include Artin approximation, arc spaces, motives and resolution of singularities. This approach yields the definability of the existential theory of Fp[[t]] (in the ring language with a constant for t) contingent upon the validity of resolution of singularities (Denef-Schoutens). Anscombe-Fehm proved a weaker result using model-theoretic tools and together with Dittmann, they gave a proof assuming only the weaker 'local uniformization conjecture.'

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)
## Wednesday seminar

Prague Set Theory Seminar

3/29/2024 2:25:55

Dear all,
The seminar meets on Wednesday April 3rd at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Sam Braunfeld -- S_infinity-invariance in random expansions and
Keisler measures
We will be concerned with randomly expanding an omega-categorical
structure M to a larger language in an Aut(M)-invariant manner. We show
that under certain conditions, such an expansion is not just
Aut(M)-invariant but fully S_infinity-invariant, which allows us to
classify such expansions. We show that the problem of classifying
Aut(M)-invariant Keisler measures on M-definable subsets may be seen as
a special case of this problem. The resulting classifications of
Aut(M)-invariant Keisler measures yield natural examples of (simple)
theories where there are non-forking formulas that are universally
measure zero.
This is joint work-in-progress with Colin Jahel and Paolo Marimon.
Best,
David

## 49th Nankai Logic Colloquium

Nankai Logic Colloquium

3/28/2024 2:16:56

Hello everyone,

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

Our speaker this week will be Aristotelis Panagiotopoulos from the Kurt Gödel Research Center. This talk is going to take place this Friday, Mar 29, from 4pm to 5pm(UTC+8, Beijing time).

Title. Strong ergodicity phenomena for Bernoulli shifts of bounded algebraic dimension

Abstract. For every Polish permutation group $P\leq \mathrm{Sym}(\mathbb{N})$ let $A\mapsto [A]_{P}$ be the assignment which maps every $A\subseteq \mathbb{N}$ to the set of all $k\in \mathbb{N}$ whose orbit under the action of the stabilizer $P_F$ of some finite $F\subseteq A$ is finite. Then $A\mapsto [A]_{P}$ is a closure operator and hence it endows $P$ with a natural notion of dimension $\mathrm{dim}(P)$. This notion of dimension has been extensively studied in model theory when $A\mapsto [A]_{P}$ satisfies additionally the \emph{exchange principle}; that is, when $A\mapsto [A]_{P}$ forms a pregeometry. However, under the exchange principle every Polish permutation group $P$ with $\mathrm{dim}(P)<\infty$ is locally compact and therefore unable to generate any ``wild" dynamics.

In this talk we will discuss the relationship between $\mathrm{dim}(P)$ and certain strong ergodicity phenomena in the absence of the exchange principle. In particular, for every $n\in\mathbb{N}$ we will provide a Polish permutation group $P$, with $\mathrm{dim}(P)=n$, whose Bernoulli shift $P\curvearrowright \mathbb{R}^{\mathbb{N}}$ is generically ergodic relative to the injective part of the Bernoulli shift of any permutation group $Q$ with $\mathrm{dim}(Q)<n$. We will use this to exhibit an equivalence relation of pinned cardinal $\aleph_1^{+}$ which strongly resembles Zapletal's counterexample to a question of Kechris, but which does not Borel reduce to the latter. Our proofs rely on the theory of symmetric models of choiceless set-theory and in the process we establish that a vast collection of symmetric models admit a theory of supports similar to the basic Cohen model. This is joint work with Assaf Shani.

___________________________________________________________________________________________________________________________________________________

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 49th Nankai Logic Colloquium -- Aristotelis Panagiotopoulos

Time ：16:00pm, Mar. 29, 2024(Beijing Time)

Zoom Number ： 734 242 5443

Passcode ：477893

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best wishes,

Ming Xiao

## Logic Seminar Talks 27 March 2024 and 3 April 2024 at NUS

NUS Logic Seminar

3/26/2024 2:52:47

Invitation to the Logic Seminar at the National University of Singapore
for the following subsequent two talks, see also the webpage
http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
(a) Date: Wednesday, 27 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Kyle Gannon
Title: Model Theoretic Events
Abstract:
This talk is motivated by the following two soft questions:
How do we sample an infinite sequence from a first order
structure? What model theoretic properties might hold on
almost all sampled sequences? We advance a plausible
framework in an attempt to answer these kinds of questions.
The central object of this talk is a proability space.
The underlying set of our space is a standard model
theoretic object, namely the space of types in countably
many variables over a monster model. Our probability measure
is an iterated Morley product of a fixed Borel-definable
Keisler measure. Choosing a point randomly in this space
with respect to our distribution yields a random generic
type in infinitely many variables. We are interested in
which model theoretic events hold for almost all random
generic types. Two different kinds of events will be discussed:
(1) The event that the induced structure on a random generic
type is isomorphic to a fixed structure;
(2) the event that a random generic type witnesses
a dividing line.
This work is joint with James Hanson.
(b) Date: Wednesday 3 April 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Frank Stephan
Title: Fuzzy Logic and Completeness
Abstract:
Fuzzy Logic allows either finitely many truth values of
the form 0,1/k,2/k,...,k/k or an infinite number of truth
values which is dense in the real interval from 0 to 1 and
which includes the two end-points 0 and 1. The specific properties
depend on the formulas chosen for calculating logical connectives;
for this talk, the following are chosen:
NOT q is 1-q;
p OR q is max{p,q};
p AND q is min{p,q};
p EOR q is min{p+q,2-p-q};
p IMPLIES q is min{1,1+q-p};
p EQUIV q is min{1+p-q,1+q-p}.
An interesting question is when is the Fuzzy Logic with these truth-values
complete in the following sense, for Propositional Logic:
One says that S logically implies alpha iff
for all truth-assignments for the atoms which make all formulas
in S have the truth value 1 it also holds that alpha has the
truth value 1. The question is now whether there is a
set of axioms for the Propositional Fuzzy Logic which allows
to prove alpha from S and these axioms.
Vilem Novak has proven in 1980 that this is the case
when there are only finitely many truth-values 0,1/k,2/k,...,k/k;
furthermore, this talk will provide a countable set S of propositional
formulas which logically imply one atoms B such that, whenever
there is an infinite set of truth-values, no finite
subset T of S logically implies B. Hence one can for infinitely
many truth-values not expect completeness, independently of
what axioms one allows. Furthermore, the set of axioms
must depend on the number of truth-values k+1 in the case
of finitely many values.
This is joint work with Neo Wei Qing and Wong Tin Lok.

## UPDATE: This Week in Logic at CUNY

This Week in Logic at CUNY

3/25/2024 11:10:24

Please note the addition of a talk in the MOPA seminar this Tuesday, 3/26 (tomorrow) by Roman Kossak.

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Mar 25, 2024 - - - -

Rutgers Logic Seminar

Monday Mar 25, 3:30pm, Hill Center, Hill 705

Arthur Apter, CUNY

A Choiceless Answer to a Question of Woodin

Logic and Metaphysics Workshop

Date: Monday, March 25, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Dan Marshall (Lingnan)

Title: A moderate theory of overall resemblance

Abstract: This paper defends the moderate theory of overall resemblance stated by: A) y is at least as similar to x as z is iff: i) every resemblance property shared by x and z is also shared by x and y, and ii) for any resemblance family of properties F, y is at least as similar to x as z is with respect to F. In this account, a resemblance property is a property that corresponds to a genuine respect in which two things can resemble each other, whereas a resemblance family is a set of properties with respect to which things can be more or less similar to each other. An example of a resemblance property is being cubical, an example of a non-resemblance property is being either a gold cube or a silver sphere, and an example of a resemblance family is the set of specific mass properties.

- - - - Tuesday, Mar 26, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Virtual (email Victoria Gitman for meeting id)

Tuesday, March 26, 1pm

Roman Kossak, CUNY

**The lattice problem for models of PA: Part ii**

The lattice problem for models of PA is to determine which lattices can be represented either as lattices of elementary substructures of a model of PA or, more generally, which can be represented as lattices of elementary substructures of a model N that contain a given elementary substructure M of N. I will talk about the history of the problem, from the seminal paper of Haim Gaifman from 1976 and other early results to some recent work of Jim Schmerl. There is much to talk about.

Computational Logic Seminar

Spring 2024 (online)

Tuesday, March 26 Time 2:00 - 4:00 PM

zoom link: contact Sergei Artemov (

sartemov@gmail.com)

Speaker: Thomas Studer, University of Bern

Title: Simplicial Complexes for Epistemic Logic

Abstract: In formal epistemology, group knowledge is often modeled as the knowledge that the group would have if the agents shared all their individual knowledge. However, this interpretation does not account for relations between agents. In this talk, we propose the notion of synergistic knowledge, which makes it possible to model different relationships between agents, e.g., groups of agents having access to shared objects. As an example, we model the problem of dining cryptographers.

- - - - Wednesday, Mar 27, 2024 - - - -

- - - - Thursday, Mar 28, 2024 - - - -

- - - - Friday, Mar 29, 2024 - - - -

** NO CLASSES AT CUNY GRADUATE CENTER **

Next Week in Logic at CUNY:

- - - - Monday, Apr 1, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, April 1, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Andrew Tedder (Vienna).

Title: Relevant logics as topical logics

Abstract: There is a simple way of reading a structure of topics into the matrix models of a given logic, namely by taking the topics of a given matrix model to be represented by subalgebras of the algebra reduct of the matrix, and then considering assignments of subalgebras to formulas. The resulting topic-enriched matrix models bear suggestive similarities to the two-component frame models developed by Berto et. al. in Topics of Thought. In this talk I’ll show how this reading of topics can be applied to the relevant logic R, and its algebraic characterisation in terms of De Morgan monoids, and indicate how we can, using this machinery and the fact that R satisfies the variable sharing property, read R as a topic-sensitive logic. I’ll then suggest how this approach to modeling topics can be applied to a broader range of logics/classes of matrices, and gesture at some avenues of research.

- - - - Tuesday, Apr 2, 2024 - - - -

- - - - Wednesday, Apr 3, 2024 - - - -

- - - - Thursday, Apr 4, 2024 - - - -

- - - - Friday, Apr 5, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, April 5, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Kameryn Williams Bard College at Simon's Rock

Logic Workshop

CUNY Graduate Center

Friday April 5, 2:00pm-3:30pm, Room 5417

Meng-Che 'Turbo' Ho, California State University at Northridge

Decision problem for groups as equivalence relations

In 1911, Dehn proposed three decision problems for finitely presented groups: the word problem, the conjugacy problem, and the isomorphism problem. These problems have been central to both group theory and logic, and were each proven to be undecidable in the 50's. There is much current research studying the decidability of these problems in certain classes of groups.

Classically, when a decision problem is undecidable, its complexity is measured using Turing reducibility. However, Dehn's problems can also be naturally thought of as computably enumerable equivalence relations (ceers). We take this point of view and measure their complexity using computable reductions. This yields behaviors different from the classical context: for instance, every Turing degree contains a word problem, but not every ceer degree does. This leads us to study the structure of ceer degrees containing a word problem and other related questions.

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)
## Set theory and topology seminar 26.03.2024 Tomasz Żuchowski

Wrocław Set Theory Seminar

3/25/2024 2:12:12

I am happy to announce that at the seminar in set theory and topology (on Tuesday 26.03.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"The Nikodym property and filters on $\omega$. Part I"

**Tomasz Żuchowski**

Abstract:

For a free filter $F$ on $\omega$, we consider the space $N_F=\omega\cup\{p_F\}$, where every element of $\omega$ is isolated and open neighborhoods of $p_F$ are of the form $A\cup\{p_F\}$ for $A\in F$.

In this talk we will study the family $\mathcal{AN}$ of such ideals $\mathcal{I}$ on $\omega$ that the space $N_{\mathcal{I}^*}$ carries a sequence $\langle\mu_n\colon n\in\omega\rangle$ of finitely supported signed measures satisfying $\|\mu_n\|\rightarrow\infty$ and $\mu_n(A)\rightarrow 0$ for every $A\in Clopen(N_{\mathcal{I}^*})$. If $\mathcal{I}\in\mathcal{AN}$ and $N_{\mathcal{I}^*}$ is embeddable into the Stone space $St(\mathcal{A})$ of a given Boolean algebra $\mathcal{A}$, then $\mathcal{A}$ does not have the Nikodym property.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/24/2024 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Mar 25, 2024 - - - -

Rutgers Logic Seminar

Monday Mar 25, 3:30pm, Hill Center, Hill 705

Arthur Apter, CUNY

A Choiceless Answer to a Question of Woodin

Logic and Metaphysics Workshop

Date: Monday, March 25, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Dan Marshall (Lingnan)

Title: A moderate theory of overall resemblance

Abstract: This paper defends the moderate theory of overall resemblance stated by: A) y is at least as similar to x as z is iff: i) every resemblance property shared by x and z is also shared by x and y, and ii) for any resemblance family of properties F, y is at least as similar to x as z is with respect to F. In this account, a resemblance property is a property that corresponds to a genuine respect in which two things can resemble each other, whereas a resemblance family is a set of properties with respect to which things can be more or less similar to each other. An example of a resemblance property is being cubical, an example of a non-resemblance property is being either a gold cube or a silver sphere, and an example of a resemblance family is the set of specific mass properties.

- - - - Tuesday, Mar 26, 2024 - - - -

Computational Logic Seminar

Spring 2024 (online)

Tuesday, March 26 Time 2:00 - 4:00 PM

zoom link: contact Sergei Artemov (

sartemov@gmail.com)

Speaker: Thomas Studer, University of Bern

Title: Simplicial Complexes for Epistemic Logic

Abstract: In formal epistemology, group knowledge is often modeled as the knowledge that the group would have if the agents shared all their individual knowledge. However, this interpretation does not account for relations between agents. In this talk, we propose the notion of synergistic knowledge, which makes it possible to model different relationships between agents, e.g., groups of agents having access to shared objects. As an example, we model the problem of dining cryptographers.

- - - - Wednesday, Mar 27, 2024 - - - -

- - - - Thursday, Mar 28, 2024 - - - -

- - - - Friday, Mar 29, 2024 - - - -

** NO CLASSES AT CUNY GRADUATE CENTER **

Next Week in Logic at CUNY:

- - - - Monday, Apr 1, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, April 1, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Andrew Tedder (Vienna).

Title: Relevant logics as topical logics

Abstract: There is a simple way of reading a structure of topics into the matrix models of a given logic, namely by taking the topics of a given matrix model to be represented by subalgebras of the algebra reduct of the matrix, and then considering assignments of subalgebras to formulas. The resulting topic-enriched matrix models bear suggestive similarities to the two-component frame models developed by Berto et. al. in Topics of Thought. In this talk I’ll show how this reading of topics can be applied to the relevant logic R, and its algebraic characterisation in terms of De Morgan monoids, and indicate how we can, using this machinery and the fact that R satisfies the variable sharing property, read R as a topic-sensitive logic. I’ll then suggest how this approach to modeling topics can be applied to a broader range of logics/classes of matrices, and gesture at some avenues of research.

- - - - Tuesday, Apr 2, 2024 - - - -

- - - - Wednesday, Apr 3, 2024 - - - -

- - - - Thursday, Apr 4, 2024 - - - -

- - - - Friday, Apr 5, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, April 5, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Kameryn Williams Bard College at Simon's Rock

Logic Workshop

CUNY Graduate Center

Friday April 5, 2:00pm-3:30pm, Room 5417

Meng-Che 'Turbo' Ho, California State University at Northridge

Decision problem for groups as equivalence relations

In 1911, Dehn proposed three decision problems for finitely presented groups: the word problem, the conjugacy problem, and the isomorphism problem. These problems have been central to both group theory and logic, and were each proven to be undecidable in the 50's. There is much current research studying the decidability of these problems in certain classes of groups.

Classically, when a decision problem is undecidable, its complexity is measured using Turing reducibility. However, Dehn's problems can also be naturally thought of as computably enumerable equivalence relations (ceers). We take this point of view and measure their complexity using computable reductions. This yields behaviors different from the classical context: for instance, every Turing degree contains a word problem, but not every ceer degree does. This leads us to study the structure of ceer degrees containing a word problem and other related questions.

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Northeast Model Theory Day

We are pleased to announce that Wesleyan University in Middletown, CT will be hosting a Northeast Model Theory Day on Saturday May 4, 2024. This one-day meeting is the first in what we hope will become an annual series, bringing together those interested in model theory from across the region.

Speakers:

Paul Baginski (Fairfield)

Artem Chernikov (Maryland)

Alf Dolich (CUNY)

Alexei Kolesnikov (Towson)

All are welcome, but please register by Monday, April 22nd. Limited travel support is available. For more information and registration, please visit

http://nemtd24.wescreates.wesleyan.edu/NEMTD 2024 sponsored by the Mid-Atlantic Mathematical Logic Seminar (NSF grant #DMS-1834219) and the Wesleyan Department of Mathematics and Computer Science.

Organizers: Alex Kruckman, Rehana Patel, Alex Van Abel. Contact

akruckman@wesleyan.edu with any questions.

- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)
## Wednesday seminar

Prague Set Theory Seminar

3/22/2024 6:37:53

Dear all,
The seminar meets on Wednesday March 27th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Egbert Thümmel -- Old questions for young people
I will present questions that arose in this seminar in the old days and
which we could not solve, but to which the young people in the seminar
will know an answer.
Best,
David

## 48th Nankai Logic Colloquium

Nankai Logic Colloquium

3/21/2024 8:53:32

Hello everyone,

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

Our speaker this week will be Dominique Lecomte from Sorbonne University. This talk is going to take place this Friday, Mar 22, from 4pm to 5pm(UTC+8, Beijing time).

Title: Descriptive properties of the irrationality type

Abstract. We present a bridge between descriptive set theory and number theory. The number-theoretic function defined by the irrationality type measures how well an irrational number can be approximated by rational numbers. We give and prove descriptive properties of the type function. In particular, it has a universality property. This is joint work with W. Banks and A. Harcharras.

___________________________________________________________________________________________________________________________________________________

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 48th Nankai Logic Colloquium -- Dominique LecomteTime ：16:00pm, Mar. 22, 2024(Beijing Time)Zoom Number ： 734 242 5443Passcode ：477893Link ：https://zoom.us/j/7342425443?pwd=NnO2EFts9VOfCR9eDFUkoI3lNn2QTo.1&omn=87996387829_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best wishes,

Ming Xiao

## Logic Seminar 20 March 2024 17:00 hrs by Sun Mengzhou

NUS Logic Seminar

3/18/2024 5:40:13

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 20 March 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Sun Mengzhou
Title: The Kaufmann-Clote question on end extensions of models of arithmetic
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
A general question in the model theory of arithmetic is:
For each theories S, T and natural number n, is it true that every
countable sufficiently saturated model of S has a proper n-elementary
end extension to a model of a T? Efforts over the past four decades
have revealed answers to this question for S and T in the
induction-collection hierarchy IΣ_n, BΣ_n, except the following
instance by Clote and Kaufmann: Is it true that, given any integer n,
every countable model of BΣ_n+2 has a proper n-elementary end extension
to a model of BΣ_n+1? We present a positive answer to the Kaufmann-Clote
question. The proof consists of a second-order ultrapower construction
based on a low basis theorem. We also include a survey on the results
related to the general question above.
This is a joint work with Tin Lok Wong and Yue Yang.

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/17/2024 22:33:00

This Week in Logic at CUNY:

- - - - Monday, Mar 18, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 18, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Michał Godziszewski (Warsaw).

Title: Modal quantifiers, potential infinity, and Yablo sequences

Abstract: When properly arithmetized, Yablo’s paradox results in a set of formulas which (with local disquotation in the background) turns out to be consistent, but omega-inconsistent. Adding either uniform disquotation or the omega-rule results in inconsistency. Since the paradox involves an infinite sequence of sentences, one might think that it doesn’t arise in finitary contexts. We study whether it does. It turns out that the issue depends on how the finitistic approach is formalized. On one of them, proposed by Marcin Mostowski, all the paradoxical sentences simply fail to hold. This happens at a price: the underlying finitistic arithmetic itself is omega-inconsistent. Finally, when studied in the context of a finitistic approach which preserves the truth of standard arithmetic, the paradox strikes back — it does so with double force, for now the inconsistency can be obtained without the use of uniform disquotation or the omega-rule.

Note: This is joint work with Rafał Urbaniak (Gdańsk).

- - - - Tuesday, Mar 19, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Tuesday, March 19, 1pm

Roman Kossak, CUNY

**The lattice problem for models of PA**

The lattice problem for models of PA is to determine which lattices can be represented either as lattices of elementary substructures of a model of PA or, more generally, which can be represented as lattices of elementary substructures of a model N that contain a given elementary substructure M of N. I will talk about the history of the problem, from the seminal paper of Haim Gaifman from 1976 and other early results to some recent work of Jim Schmerl. There is much to talk about.

**Computational Logic Seminar **

**Spring 2024 ****(online)**

**Tuesday, March 19, ****Time 2:00 - 4:00 PM **

**Speaker**: **Tudor Protopopescu**, *CUNY*

**Title:*** **Logics of Intuitionistic Knowledge and Verification*

**Abstract: **We present intuitionistic epistemic systems IEL-, IEL and IEL+, systems of verification based belief, knowledge and strict knowledge. The intuitionistic epistemic language captures basic reasoning about intuitionistic knowledge and belief, but its language has expressive limitations. Following Gödel's explication of IPC as a fragment of the more expressive system of classical modal logic S4, we present a faithful embedding of the intuitionistic systems into S4 extended with a verification modality. These systems in turn have explicit counterparts in the Logic of Proofs extended with a verification modality.

- - - - Wednesday, Mar 20, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Sina Hazratpour, Johns Hopkins University.**

Date and Time: ** Wednesday March 20, 2024, 7:00 - 8:30 PM.**

Title:** Fibred Categories in Lean.**

Abstract: Fibred categories are one of the most important and useful concepts in category theory and its application in categorical logic. In this talk I present my recent formalization of fibred categories in the interactive theorem prover Lean 4. I begin by highlighting certain technical challenges associated with handling the equality of objects and functors within the extensional dependent type system of Lean, and how they can be overcome. In this direction, I will demonstrate how we can take advantage of dependent coercion, instance synthesis, and automation tactics from the Lean toolbox. Finally I will discuss a formalization of Homotopy Type Theory in Lean 4 using a fired categorical framework.

- - - - Thursday, Mar 21, 2024 - - - -

- - - - Friday, Mar 22, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 22, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

**Arthur Apter**, CUNY

**A choiceless answer to a question of Woodin**

In a lecture presented in July 2023, Moti Gitik discussed the following question from the 1980s due to Woodin, as well as approaches to its solution and why it is so difficult to solve:

Question: Assuming there is no inner model of ZFC with a strong cardinal, is it possible to have a model M of ZFC such that M⊨'2ℵω>ℵω+2 and 2ℵn=ℵn+1 for every n<ω', together with the existence of an inner model N∗⊆M of ZFC such that for the γ,δ so that γ=(ℵω)M and δ=(ℵω+3)M, N∗⊨'γ is measurable and 2γ≥δ'?I will discuss how to find answers to this question, if we drop the requirement that M satisfies the Axiom of Choice. I will also briefly discuss the phenomenon that on occasion, when the Axiom of Choice is removed from consideration, a technically challenging question or problem becomes more tractable. One may, however, end up with models satisfying conclusions that are impossible in ZFC.

Reference: A. Apter, 'A Note on a Question of Woodin', *Bulletin of the Polish Academy of Sciences (Mathematics)*, volume 71(2), 2023, 115--121.

Logic Workshop

CUNY Graduate Center

Friday Mar 22, 2:00pm-3:30pm, Room 5417

**Mediate cardinals**

In the late 1910s Bertrand Russell was occupied with two things: getting into political trouble for his pacifism and trying to understand the foundations of mathematics. His students were hard at work with him on this second occupation. One of those students was Dorothy Wrinch. In 1923 she gave a characterization of the axiom of choice in terms of a generalization of the notion of a Dedekind-finite infinite set. Unfortunately, her career turned toward mathematical biology and her logical work was forgotten by history.

This talk is part of a project of revisiting Wrinch's work from a modern perspective. I will present the main result of her 1923 paper, that AC is equivalent to the non-existence of what she termed mediate cardinals. I will also talk about some new independence results. The two main results are: (1) the smallest κ for which a κ-mediate cardinal exists can consistently be any regular κ and (2) the collection of regular κ for which exact κ-mediate cardinals exist can consistently be any class.

Next Week in Logic at CUNY:

- - - - Monday, Mar 25, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 25, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Dan Marshall (Lingnan)

Title: A moderate theory of overall resemblance

Abstract: This paper defends the moderate theory of overall resemblance stated by: A) y is at least as similar to x as z is iff: i) every resemblance property shared by x and z is also shared by x and y, and ii) for any resemblance family of properties F, y is at least as similar to x as z is with respect to F. In this account, a resemblance property is a property that corresponds to a genuine respect in which two things can resemble each other, whereas a resemblance family is a set of properties with respect to which things can be more or less similar to each other. An example of a resemblance property is being cubical, an example of a non-resemblance property is being either a gold cube or a silver sphere, and an example of a resemblance family is the set of specific mass properties.

- - - - Tuesday, Mar 26, 2024 - - - -

- - - - Wednesday, Mar 27, 2024 - - - -

- - - - Thursday, Mar 28, 2024 - - - -

- - - - Friday, Mar 29, 2024 - - - -

** NO CLASSES AT CUNY GRADUATE CENTER **

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Groups, Logic, and Dynamics

This is the second installment of the meeting in Groups, Logic and Dynamics. We will be meeting in New Brunswick at the beginning of the spring season.

WHERE: Rutgers, The State University of New Jersey.

WHEN: Saturday, March 23

- - - - Web Site - - - -Find us on the web at: nylogic.github.io(site designed, built & maintained by Victoria Gitman)
## KGRC Talk - March 21

Kurt Godel Research Center

3/15/2024 12:17:58

KGRC/Institute of Mathematics invites you to the following
Set Theory Seminar talk:
”(Piecewise) convexembeddability on linear orders”
M. Iannella (TU Wien)
Kolingasse 14–16, 1090, 1st floor, SR 10,
Thursday, March 21, 11:30am–1:00pm, hybride mode
Given a nonempty set $\mathcal{L}$ of linear orders, we say that the linear order $L$ is $\mathcal{L}$-convex embeddable into the linear order $L'$ if it is possible to partition $L$ into convex sets, indexed by some element of $\mathcal{L}$, which are isomorphic to convex subsets of $L'$ ordered in the same way. This notion generalizes convex embeddability and (finite) piecewise convex embeddability, which arise from the special cases $\mathcal{L}=\{\mathbf{1}\}$ and $\mathcal{L}=\mathsf{Fin}$. In this talk we focus on the behaviour of these relations on the set of countable linear orders, first characterising when they are transitive, and hence a quasi-order. We then look at some combinatorial properties and complexity (with respect to Borel reducibility) of these quasi-orders. Finally, we analyse their extension to uncountable linear orders.
The presented results stem from joint work with Alberto Marcone, Luca Motto Ros, and Vadim Weinstein.
Zoom info: If you have not received the Zoom data by the day before the talk, please contact petra.czarnecki@univie.ac.at.
Please direct any questions about this talk to vera.fischer@univie.ac.at.
*******
Video recordings available so far of the Set Theory Seminar:
March, 7: S. Hovath (ETH Zurich, CH, "Magic Sets"
https://ucloud.univie.ac.at/index.php/s/LeTqoZN7aHCqDd5
March, 7: F. Uribe Zapata (TU Wien), "A general theory of iterated
forcing using finitely additive measures"
https://ucloud.univie.ac.at/index.php/s/kEwfXg8PNFp44MC
*******
Updates at https://kgrc.univie.ac.at/eventsnews/
--
Mag. Petra Czarnecki de Czarnce-Chalupa
Institute of Mathematics (Kurt Goedel Research Center, Logic)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## Set theory and topology seminar 19.03.2024 Piotr Szewczak

Wrocław Set Theory Seminar

3/14/2024 15:13:37

I am happy to announce that at the seminar in set theory and topology (on Tuesday 19.03.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"Perfectly meager sets in the transitive sense and the Hurewicz property"

**Piotr Szewczak (UKSW)**

Abstract:

We work in the Cantor space with the usual group operation +. A set X is *perfectly meager in the transitive sense* if for any perfect set P there is an F-sigma set F containing X such that for every point t the intersection of t+F and P is meager in the relative topology of P. A set X is *Hurewicz* if for any sequence of increasing open covers of X one can select one set from each cover such that the chosen sets formulate a gamma-cover of X, i.e., an infinite cover such that each point from X belongs to all but finitely many sets from the cover. Nowik proved that each Hurewicz set which cannot be mapped continuously onto the Cantor set is perfectly meager in the transitive sense. We answer a question of Nowik and Tsaban, whether of the same assertion holds for each Hurewicz set with no copy of the Cantor set inside. We solve this problem, under CH, in the negative.

This is a joint work with Tomasz Weiss and Lyubomyr Zdomskyy.

The research was funded by the National Science Centre, Poland and the Austrian Science Found under the Weave-UNISONO call in the Weave programme, project: Set-theoretic aspects of topological selections 2021/03/Y/ST1/00122

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## Wednesday seminar

Prague Set Theory Seminar

3/14/2024 10:31:23

Dear all,
The seminar meets on Wednesday March 20th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Allen Gehret -- Asymptotic couples and set theory
The subject ``asymptotic differential algebra'' has recently gained
attention with the tremendous landmark results of Aschenbrenner, van den
Dries, and van der Hoeven in the volume ``Asymptotic differential
algebra and model theory of transseries''. In this talk I will describe
a small piece of this world which I have been investigating, and its
connection to set theory. The outline of the talk is as follows:
I. 1-variable calculus, a "review"
II. Asymptotic couples
III. Dividing lines and set-theoretic independence results
IV. Current/future work? (joint with Elliot Kaplan, Nigel Pynn-Coates,...)
Best,
David

## 47th Nankai Logic Colloquium

Nankai Logic Colloquium

3/13/2024 23:16:38

Hello everyone,

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

Our speaker this week will be Sumun Iyer from Cornell University. This talk is going to take place this Friday, Mar 15, from 9am to 10am(UTC+8, Beijing time).

Title: Extremely amenable groups of homeomorphisms

Abstract: A topological group is extremely amenable if every continuous action of it on a compact Hausdorff space has a fixed point. We will first survey some known results/ general tools about extreme amenability for homeomorphism groups of connected compact spaces. We discuss a construction due to Uspenskij which gives a condition equivalent to extreme amenability for this setting. We then show a Ramsey-type statement for subsets of simplices that, together with Uspenskij's construction, gives a new proof of a theorem due to Pestov: that the group of orientation-preserving homeomorphisms of the closed unit interval is extremely amenable. This is a joint work with Lukas Michel and Alex Scott.

___________________________________________________________________________________________________________________________________________________

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 47th Nankai Logic Colloquium -- Sumun Iyer

Time ：9:00am, Mar. 15, 2024(Beijing Time)

Zoom Number ： 734 242 5443

Passcode ：477893

Link ：https://zoom.us/j/7342425443?pwd=EG6I3uatr8anqkk6HM5wZ9FKjhkjbC.1&omn=87197636384

_____________________________________________________________________

Best wishes,

Ming Xiao

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/10/2024 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Mar 11, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 11, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Otávio Bueno (Miami)

Title: Dispensing with the grounds of logical necessity

Abstract: Logical laws are typically conceived as being necessary. But in virtue of what is this the case? That is, what are the grounds of logical necessity? In this paper, I examine four different answers to this question in terms of: truth-conditions, invariance of truth-values under different interpretations, possible worlds, and brute facts. I ultimately find all of them wanting. I conclude that an alternative conception of logic that dispenses altogether with grounds of logical necessity provides a less troublesome alternative. I then indicate some of the central features of this conception.

- - - - Tuesday, Mar 12, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Tuesday, March 12, 1pm

Albert Visser, Utrecht University

**Restricted completions**

This talk reports on research in collaboration with Ali Enayat and Mateusz Łełyk.

Steffen Lempp and Dino Rossegger asked: is there a consistent completion of PA− that is axiomatised by sentences of bounded quantifier-alternation complexity? We show that there is no such restricted completion. We also show that, if one changes the measure of complexity to being Σn, there is a restricted completion. Specifically, we show that the true theory of the non-negative part of Z[X] can be axiomatised by a single sentence plus a set of Σ01-sentences.In our talk we will sketch these two answers. One of our aims is to make clear is that the negative answer for the case of quantifier-alternation complexity simply follows from Rosser's Theorem viewed from a sufficiently abstract standpoint.

- - - - Wednesday, Mar 13, 2024 - - - -

- - - - Thursday, Mar 14, 2024 - - - -

- - - - Friday, Mar 15, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 15, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Chris Lambie-Hanson, Czech Academy of Sciences

**Squares, ultrafilters and forcing axioms**

A uniform ultrafilter U over a cardinal κ>ω1 is called *indecomposable* if, whenever λ<κ and f:κ→λ, there is a set X∈U such that f[X] is countable. Indecomposability is a natural weakening of κ-completeness and has a number of implications for, e.g., the structure of ultraproducts. In the 1980s, Sheard answered a question of Silver by proving the consistency of the existence of an inaccessible but not weakly compact cardinal carrying an indecomposable ultrafilter. Recently, however, Goldberg proved that this situation cannot hold above a strongly compact cardinal: If λ is strongly compact and κ≥λ carries an indecomposable ultrafilter, then κ is either measurable or a singular limit of countably many measurable cardinals. We prove that the same conclusion follows from the Proper Forcing Axiom, thus adding to the long list of statements first shown to hold above a strongly compact or supercompact cardinal and later shown also to follow from PFA. Time permitting, we will employ certain indexed square principles to prove that our results are sharp. This is joint work with Assaf Rinot and Jing Zhang.

Logic Workshop

CUNY Graduate Center

Friday Mar 15, 2:00pm-3:30pm, Room 5417

Michał Godziszewski, University of Warsaw

**Tennebaum's Theorem for quotient presentations and model-theoretic skepticism**

A computable quotient presentation of a mathematical structure A consists of a computable structure on the natural numbers ⟨N,⋆,∗,…⟩, meaning that the operations and relations of the structure are computable, and an equivalence relation E on N, not necessarily computable but which is a congruence with respect to this structure, such that the quotient ⟨N,⋆,∗,…⟩ is isomorphic to the given structure A. Thus, one may consider computable quotient presentations of graphs, groups, orders, rings and so on.

A natural question asked by B. Khoussainov in 2016, is if the Tennenbaum Thoerem extends to the context of computable presentations of nonstandard models of arithmetic. In a joint work with J.D. Hamkins we have proved that no nonstandard model of arithmetic admits a computable quotient presentation by a computably enumerable equivalence relation on the natural numbers.

However, as it happens, there exists a nonstandard model of arithmetic admitting a computable quotient presentation by a co-c.e. equivalence relation. Actually, there are infinitely many of those. The idea of the proof consists is simulating the Henkin construction via finite injury priority argument. What is quite surprising, the construction works (i.e. injury lemma holds) by Hilbert's Basis Theorem. The latter argument is joint work with T. Slaman and L. Harrington.

Next Week in Logic at CUNY:

- - - - Monday, Mar 18, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 18, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Michał Godziszewski (Warsaw).

Title: Modal quantifiers, potential infinity, and Yablo sequences

Abstract: When properly arithmetized, Yablo’s paradox results in a set of formulas which (with local disquotation in the background) turns out to be consistent, but omega-inconsistent. Adding either uniform disquotation or the omega-rule results in inconsistency. Since the paradox involves an infinite sequence of sentences, one might think that it doesn’t arise in finitary contexts. We study whether it does. It turns out that the issue depends on how the finitistic approach is formalized. On one of them, proposed by Marcin Mostowski, all the paradoxical sentences simply fail to hold. This happens at a price: the underlying finitistic arithmetic itself is omega-inconsistent. Finally, when studied in the context of a finitistic approach which preserves the truth of standard arithmetic, the paradox strikes back — it does so with double force, for now the inconsistency can be obtained without the use of uniform disquotation or the omega-rule.

Note: This is joint work with Rafał Urbaniak (Gdańsk).

Speaker: ** Sina Hazratpour, Johns Hopkins University.**

Date and Time: ** Wednesday March 20, 2024, 7:00 - 8:30 PM.**

Title:** Fibred Categories in Lean.**

Abstract: Fibred categories are one of the most important and useful concepts in category theory and its application in categorical logic. In this talk I present my recent formalization of fibred categories in the interactive theorem prover Lean 4. I begin by highlighting certain technical challenges associated with handling the equality of objects and functors within the extensional dependent type system of Lean, and how they can be overcome. In this direction, I will demonstrate how we can take advantage of dependent coercion, instance synthesis, and automation tactics from the Lean toolbox. Finally I will discuss a formalization of Homotopy Type Theory in Lean 4 using a fired categorical framework.

- - - - Thursday, Mar 21, 2024 - - - -

- - - - Friday, Mar 22, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 22, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

**Arthur Apter**, CUNY

**A choiceless answer to a question of Woodin**

In a lecture presented in July 2023, Moti Gitik discussed the following question from the 1980s due to Woodin, as well as approaches to its solution and why it is so difficult to solve:

Question: Assuming there is no inner model of ZFC with a strong cardinal, is it possible to have a model M of ZFC such that M⊨'2ℵω>ℵω+2 and 2ℵn=ℵn+1 for every n<ω', together with the existence of an inner model N∗⊆M of ZFC such that for the γ,δ so that γ=(ℵω)M and δ=(ℵω+3)M, N∗⊨'γ is measurable and 2γ≥δ'?I will discuss how to find answers to this question, if we drop the requirement that M satisfies the Axiom of Choice. I will also briefly discuss the phenomenon that on occasion, when the Axiom of Choice is removed from consideration, a technically challenging question or problem becomes more tractable. One may, however, end up with models satisfying conclusions that are impossible in ZFC.

Reference: A. Apter, 'A Note on a Question of Woodin', *Bulletin of the Polish Academy of Sciences (Mathematics)*, volume 71(2), 2023, 115--121.

Logic Workshop

CUNY Graduate Center

Friday Mar 22, 2:00pm-3:30pm, Room 5417

Kameryn Williams Bard College at Simon's Rock

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Groups, Logic, and Dynamics

This is the second installment of the meeting in Groups, Logic and Dynamics. We will be meeting in New Brunswick at the beginning of the spring season.

WHERE: Rutgers, The State University of New Jersey.

WHEN: Saturday, March 23

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## KGRC Talks - March 11-15

Kurt Godel Research Center

3/8/2024 4:25:12

KGRC/Institute of Mathematics invites you to the following talks:
(updates at https://kgrc.univie.ac.at/eventsnews/)
Set Theory Seminar
Kolingasse 14–16, 1090, 1st floor, SR 10,
Thursday, March 14, 11:30am–1:00pm.
”How economists forgot about multi-player utility and how we remembered”
D. Schrittesser (Harbin Institute of Technology, Harbin, CN)
This is all joint work with Ali M. Khan (Johns Hopkins) and Paul Arthur
Pedersen (CUNY).
Game theory as practiced by economists is often couched in a setting
where players pick strategies, and
then a utility function tells them who has which pay off (the so-called
”normal form” of a game). For two
person games, an important special case is the zero sum game: the case
where pay offs always sum to zero.
Aumann, the sixties, defined ”strictly competitive games”, two player
games in which what is good for one
player is bad for the other. Aumann frequently stated that this is the
same class as the zero sum games—for
an appropriate choice of utility function (and provided the players
strategy spaces are closed under mixing).
We claim that Aumann must have known this because he knew the
multidimensional theory of utility. But
then in 2009, Adler, Daskalakis and Papadimitriou gave a non-trivial
proof of the fact claimed by Aumann,
for finite games, claiming that no such proof exists in the literature.
This was generalized in 2023 by Rai-
mondo to games where the set of strategies available to each player is
an appropriate set of probability
measures on [0,1] (or if you’re feeling fancy, on a standard Borel space).
In this talk, I shall show what Aumann and others must already have been
aware of, but what has apparently
been forgotten in the meantime: That these results, and more general
ones, follow easily from the theory
of mutlidimensional utility developed in the 60ies and early 70ies by
Fishburn, Roberts, and others.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at.
Please direct any questions about this talk to vera.fischer@univie.ac.at.
* * * * * * * * *
Logic Colloquium
Oskar-Morgenstern-Platz 1, 1090, 2nd floor, HS 11,
Thursday, March 14, 3:00pm–3:50pm, hybrid mode
”Projective Fraisse limits of trees”
Aleksandra Kwiatkowska (University of Münster, DE*)*
We continue the study of projective Fraisse limits developed by
Irwin-Solecki and Panagiotopoulos-Solecki by investigating families of
epimorphisms between finite trees and finite rooted trees.
We focus on particular classes of epimorphisms such as monotone,
confluent or simple confluent, which are adaptations to graphs of
monotone or confluent maps from continuum theory. As the topological
realizations of the projective Fraisse limits we obtain the dendrite D_3
the Mohler-Nikiel universal dendroid, as well as new, interesting
compact connected spaces (continua) for which we do not yet have
topological characterizations.
The talk is based on joint work with Charatonik, Roe, Yang.
Zoom info: If you have not received the Zoom data by the day before the
talk, please contact petra.czarnecki@univie.ac.at.
Please direct any questions about this talk to
aristotelis.panagiotopoulos@univie.ac.at.

## Set theory and topology seminar 12.03.2024 Grigor Sargsyan

Wrocław Set Theory Seminar

3/6/2024 10:06:30

I am happy to announce that at the seminar in set theory and topology (on Tuesday 12.03.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"Forcing extensions of models of determinacy"

**Grigor Sargsyan (IMPAN)**

Abstract:

We will give an overview of what has been recently forced over models of determinacy. In particular, we will

explain how to obtain combinatorially rich ZFC extensions by forcing over a model of determinacy axioms. Part of this work\

are joint with Paul Larson and Douglas Blue.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## Wednesday seminar

Prague Set Theory Seminar

3/6/2024 6:32:52

Dear all,
The seminar meets on Wednesday March 13th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Stefan Geschke -- Separating Borel chromatic numbers
We discuss various graphs on the Cantor space and discuss the question
whether their Borel chromatic numbers can consistently be different.
Moreover, there will be an extra seminar this week, Friday March 8th,
14:00--15:30, Institute of Mathematics CAS, seminar room Konirna,
organized by Wieslaw Kubis.
Program: Lionel Nguyen Van The -- Revisiting the Erdös-Rado canonical
partition theorem
One of the numerous strengthenings of Ramsey's theorem is due to Erdös
and Rado, who analyzed what partition properties can be obtained on
m-subsets of the naturals when colorings are not necessarily finite.
Large monochromatic sets may not appear in that case, but there is a
finite list of behaviors, called "canonical", to which every coloring
reduces. The purpose of this talk will be to remind certain not so well
known analogous theorems of the same flavor that were obtained by Prömel
in the eighties for various classes of structures (like graphs or
hypergraphs), and to show how such theorems can in fact be deduced in
the more general setting of Fraïssé classes.
Best,
David

## KGRC Set Theory Talks - March 4-8

Kurt Godel Research Center

3/5/2024 11:59:07

The KGRC welcomes as guests:

Alexi Block Gorman, Ohio State University, Columbus, US (host:
Matthias Aschenbrenner) visits March 3–9

Elliot Kaplan, McMaster University, Hamilton, CA, Columbus, US
(host: Nigel Pynn-Coates) visits March 3–9

Silvan Horvath, ETH Zurich, CH (host: Vera Fischer) visits March
4–July 31

* * * * * * * * *

KGRC/Institute of Mathematics invites you to the following talks:

(updates at

https://kgrc.univie.ac.at/) )

**SET THEORY SEMINAR**
Kolingasse 14–16, 1090, 1st floor, SR 10,

Thursday, March 7, 11:30am – 12:00pm, hybrid mode

**”Magic Sets”**

S. Horvath (ETH Zurich, CH)
A Magic Set is a set M of reals with the property that for all
nowhere constant, continuous functions f and

g on the reals it holds that f [M ] ⊆ g[M ] implies f = g.

I will cover some of the basic results on magic sets and introduce
magic forcing - a forcing notion that adds

a new magic set to the ground model.

Zoom: If you have not received the Zoom data by the day before the
talk, please contact

petra.czarnecki@univie.ac.at.

Meeting ID: 671 1734 6051

Passcode: kgrc

Please direct any questions about this talk to

vera.fischer@univie.ac.at.

* * * * * * * * *

**SET THEORY SEMINAR**
Kolingasse 14–16, 1090, 1st floor, SR 10,

Thursday, March 7, 12:00pm – 13:00pm, hybrid mode

**”A general theory of iterated forcing using finitely additive
measures”**

A. F. Uribe Zapata (TU Wien)
Saharon Shelah in 2000 introduced a finite-support iteration using
finitely additive measures to prove that,

consistently, the covering of the null ideal may have countable
cofinality. In 2019, Jakob Kellner, Saharon

Shelah, and Anda R. T ̆anasie achieved some new results and
applications using such iterations.

In this talk, based on the works mentioned above, we present a
general theory of iterated forcing using

finitely additive measures, which was developed in the speaker’s
master’s thesis. For this purpose, we intro-

duce two new notions: on the one hand, we define a new linkedness
property, which we call ”FAM-linked”

and, on the other hand, we generalize the idea of intersection
number to forcing notions, which justifies the

limit steps of our iteration theory. Finally, we show a new
separation of the left-side of Cicho ́n’s diagram

allowing a singular value.

Zoom info

Zoom: If you have not received the Zoom data by the day before the
talk, please contact

petra.czarnecki@univie.ac.at.

Passcode: kgrc

Please direct any questions about this talk to

vera.fischer@univie.ac.at.

* * * * * * * * *

**VIDEO** recordings available so far of the

**LOGIC
COLLOQUIUM:**
January 25: Y. Khomskii (Amsterdam U College, NL and U Hamburg,
DE) "Trees, Transcendence and Quasi-generic
reals"

https://ucloud.univie.ac.at/index.php/s/Wd9DPzXqQsnBPzC
November 16: D. A. Mejía (Shizuoka U, JP) ”Iterations with
ultrafilter-limits and fam-limits”

https://ucloud.univie.ac.at/index.php/s/T6pD2XgwTfNPYtn
—–

The LECTURE NOTE for Diego Mejía’s mini-course available so far of
the Set Theory Seminar:

January 25: D. A. Mejıa (Shizuoka U, JP) ”Forcing techniques for
Cicho ́n’s Maximum”

https://mathematik.univie.ac.at/fileadmin/user_upload/f_mathematik/Events_News/Vortraege_Events/2023-24/20240122_Mejia_minicourse-1.pdf.

**VIDEO **recordings available so far of the

**SET THEORY
SEMINAR**:

January 25: D. A. Mejía (Shizuoka U, JP), ”Forcing techniques for
Cicho ́n’s Maximum VI” video:

https://ucloud.univie.ac.at/index.php/s/8EyKfLZW3NBH4f2
January 18: D. A. Mejía (Shizuoka U, JP), ”Forcing techniques for
Cicho ́n’s Maximum V”
video:

https://ucloud.univie.ac.at/index.php/s/QrKjY6CYtJMx7WT
January 11: D. A. Mejía (Shizuoka U, JP), ”Forcing techniques for
Cicho ́n’s Maximum IV”

https://ucloud.univie.ac.at/index.php/s/KFpbqsLjQm3tcKn
## NUS Logic Seminar Talk by Rupert Hoelzl on 6 March 2024 17:00 hrs

NUS Logic Seminar

3/5/2024 0:20:55

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 6 March 2024, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Rupert Hoelzl, Universitaet der Bundeswehr, Munich
Title: Benign approximations and non-speedability
Abstract:
A left-computable number x is called regainingly approximable if
there is a computable increasing sequence (x_n)_{n in N} of
rational numbers converging to x such that x-x_n < 2^-n.
for infinitely many n in N; and it is called nearly computable if
there is such an (x_n)_n such that for every computable increasing
function s:N -> N the sequence (x_{s(n+1)}-x_{s(n)}){n in N}
converges computably to 0.
In this talk we study the relationship between both concepts
by constructing on the one hand a non-computable number that is
both regainingly approximable and nearly computable, and on the
other hand a left-computable number that is nearly computable
but not regainingly approximable; it then easily follows that
the two notions are incomparable with non-trivial intersection.
With this relationship clarified, we then hold the keys to
answering an open question of Merkle and Titov: they studied
speedable numbers, that is, left-computable numbers whose
approximations can be sped up in a certain sense, and asked
whether, among the left-computable numbers,
being Martin-Loef random is equivalent to being non-speedable.
As we show that the concepts of speedable and regainingly
approximable numbers are equivalent within the nearly
computable numbers, our second construction provides a negative answer.
This is joint work with Philip Janicki.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## Set theory and topology seminar 5.03.2024 Agnieszka Widz

Wrocław Set Theory Seminar

3/4/2024 1:13:20

I am happy to announce that at the seminar in set theory and topology (on Tuesday 5.03.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

**Agnieszka Widz**

Abstract:

The Random Graph can be generated almost surely by connecting vertices with a fixed probability $p\in(0,1)$, independently of other pairs. In my talk, I will recall the construction and explore interesting properties of the Random Graph, investigating the impact of varying probabilities for each edge. Specifically, I will characterize sequences $(p_n)_{n\in\IN}$ for which there exists a bijection $f$ between pairs of vertices in $\IN$, such that if we connect vertices $v$ and $w$ with probability $p_{f(\{v,w\})}$, the Random Graph emerges almost surely.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## This Week in Logic at CUNY

This Week in Logic at CUNY

3/3/2024 22:44:00

This Week in Logic at CUNY:

- - - - Monday, Mar 4, 2024 - - - -

Rutgers Logic Seminar

Monday, March 4, 3:30pm, Rutgers University, Hill 705

Sean Cox, Virginia Commonwealth

Sparse systems, CH, and Denjoy-Carleman classes

Abstract: Hardin and Taylor proved that, for any set $S$, a wellordering of ${}^{\mathbb{R}} S$ allows one to build a "predictor" $\mathcal{P}$ for partial functions from $\mathbb{R} \to S$, in the sense that for any total $F \in {}^{\mathbb{R}} S$, $\mathcal{P}(F \restriction (-\infty,t)) = F(t)$ for almost every $t \in \mathbb{R}$. They asked: for which classes $\Gamma \subseteq \text{Homeo}^+(\mathbb{R})$ could one further arrange that $\mathcal{P}$ is invariant with respect to precomposition with members of $\Gamma$? Subsequent work of Hardin-Taylor, Bajpai-Velleman, and my joint work with Aldi, Buffkin, Cline, Cody, Elpers, and Lee have made progress on this problem. This talk will focus on the negative direction: if $\Gamma$ carries a "sparse system", then there is no $\Gamma$-invariant predictor. In recent work with Aldi, Buffkin, and Cline, we proved that 1) sparse systems always exist for "non-quasi-analytic" Denjoy-Carleman classes, and 2) CH holds if and only if some--equivalently, every--quasi-analytic Denjoy Carleman class carries a sparse system. The latter strengthens the previous Cody-Cox-Lee result that CH is equivalent to existence of a sparse analytic system.

Logic and Metaphysics Workshop

Date: Monday, March 4, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Elise Crull (CUNY).

Title: Declaring no dependence

Abstract: Viable fundamental ontologies require at least one suitably stable, generic-yet-toothy metaphysical dependence relation to establish fundamentality. In this talk I argue that recent experiments in quantum physics using Page-Wootters devices to model global vs. local dynamics cast serious doubt on the existence of such metaphysical dependence relations when – and arguably, inevitably within any ontological framework – physical systems serve as the relata.

- - - - Tuesday, Mar 5, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Tuesday, March 5, 1pm

Piotr Gruza University of Warsaw

**Tightness and solidity in fragments of Peano Arithmetic**

It was shown by Visser that Peano Arithmetic has the property that no two distinct extensions of it (in its language) are bi-interpretable. Enayat proposed to refer to this property of a theory as *tightness* and to carry out a more systematic study of tightness and its stronger variants, which he called *neatness* and *solidity*.

Enayat proved that not only PA, but also ZF, Z2, and KM are solid; and on the other hand, that finitely axiomatisable fragments of them are not even tight. Later work by a number of authors showed that many natural proper fragments of these theories are also not tight.

Enayat asked whether there are proper solid subtheories (containing some basic axioms that depend on the theory) of the theories listed above. We answer this question in the case of PA by proving that for every n there exists a solid theory strictly between IΣn and PA. Furthermore, we can require that the theory does not interpret PA, and that if any true arithmetic sentence is added to it, the theory still does not prove PA.

Joint work with Leszek Kołodziejczyk and Mateusz Łełyk.

Computational Logic Seminar

Spring 2024 (online) For a zoom link

contact S.ArtemovTuesday, March 5, Time 2:00 - 4:00 PM

Speaker: Sergei Artemov, Graduate Center

Title: On Tolerance Analysis in Extensive-Form Games.

Abstract: Epistemic assumptions, including rationality of actors, can change during the game, e.g., due to unexpected moves of players. We discuss a body of examples and outline the corresponding logic foundation of belief revision in games.

- - - - Wednesday, Mar 6, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Jean-Pierre Marquis, Universite de Montreal.**

Date and Time: ** Wednesday March 6, 2024, 7:00 - 8:30 PM. IN PERSON TALK!**

Title:** Hom sweet Hom: a sketch of the history of duality in category theory.**

Abstract: Duality, in its various forms and roles, played a surprisingly important part in the development of category theory. In this talk, I will concentrate on the development of these forms and roles that lead to the categorical formulation of Stone-type dualities in the 1970s. I will emphasize the epistemological gain and loss along the way.

- - - - Thursday, Mar 7, 2024 - - - -

- - - - Friday, Mar 8, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 8, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Jonathan Osinski University of Hamburg

We consider logics in which the collection of sentences over a set-sized vocabulary can form a proper class. The easiest example of such a logic is L∞∞, which allows for disjunctions and conjunctions over arbitrarily sized sets of formulas and quantification over strings of variables of any infinite length. Model theory of L∞∞ is very restricted. For instance, it is inconsistent for it to have nice compactness or Löwenheim-Skolem properties. However, Trevor Wilson recently showed that the existence of a Löwenheim-Skolem-Tarski number of a certain class-sized fragment of L∞∞ is equivalent to the existence of a supercompact cardinal, and various other related results. We continue this work by considering several appropriate class-sized logics and their relations to large cardinals. This is joint work with Trevor Wilson.

Next Week in Logic at CUNY:

- - - - Monday, Mar 11, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, March 11, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Otávio Bueno (Miami)

Title: Dispensing with the grounds of logical necessity

Abstract: Logical laws are typically conceived as being necessary. But in virtue of what is this the case? That is, what are the grounds of logical necessity? In this paper, I examine four different answers to this question in terms of: truth-conditions, invariance of truth-values under different interpretations, possible worlds, and brute facts. I ultimately find all of them wanting. I conclude that an alternative conception of logic that dispenses altogether with grounds of logical necessity provides a less troublesome alternative. I then indicate some of the central features of this conception.

- - - - Tuesday, Mar 12, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Tuesday, March 12, 1pm

Albert Visser, Utrecht University

**Restricted completions**

This talk reports on research in collaboration with Ali Enayat and Mateusz Łełyk.

Steffen Lempp and Dino Rossegger asked: is there a consistent completion of PA− that is axiomatised by sentences of bounded quantifier-alternation complexity? We show that there is no such restricted completion. We also show that, if one changes the measure of complexity to being Σn, there is a restricted completion. Specifically, we show that the true theory of the non-negative part of Z[X] can be axiomatised by a single sentence plus a set of Σ01-sentences.In our talk we will sketch these two answers. One of our aims is to make clear is that the negative answer for the case of quantifier-alternation complexity simply follows from Rosser's Theorem viewed from a sufficiently abstract standpoint.

- - - - Wednesday, Mar 13, 2024 - - - -

- - - - Thursday, Mar 14, 2024 - - - -

- - - - Friday, Mar 15, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 15, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Chris Lambie-Hanson, Czech Academy of Sciences

Logic Workshop

CUNY Graduate Center

Friday Mar 15, 2:00pm-3:30pm, Room 5417

Michał Godziszewski, University of Warsaw

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Groups, Logic, and Dynamics

This is the second installment of the meeting in Groups, Logic and Dynamics. We will be meeting in New Brunswick at the beginning of the spring season.

WHERE: Rutgers, The State University of New Jersey.

WHEN: Saturday, March 23

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

3/1/2024 9:36:33

Dear all,
Due to the scheduled water supply outage in the Institute next
Wednesday, the seminar is cancelled next week (March 6th). Stefan's talk
will take place one week later, Wednesday March 13th. I will send one
more regular announcement during week before the seminar.
Best,
David
On 29/02/2024 21:05, David Chodounsky wrote:
> Dear all,
>
> The seminar meets on Wednesday March 6th at 11:00 in the Institute of
> Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
>
>
> Program: Stefan Geschke -- Separating Borel chromatic numbers
>
> We discuss various graphs on the Cantor space and discuss the question
> whether their Borel chromatic numbers can consistently be different.
>
>
> Best,
> David

## Wednesday seminar

Prague Set Theory Seminar

2/29/2024 15:05:12

Dear all,
The seminar meets on Wednesday March 6th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Stefan Geschke -- Separating Borel chromatic numbers
We discuss various graphs on the Cantor space and discuss the question
whether their Borel chromatic numbers can consistently be different.
Best,
David

## 45th Nankai Logic Colloquium

Nankai Logic Colloquium

2/29/2024 1:51:04

Hello everyone,

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

Our speaker this week will be Takayuki Kihara from Nagoya University. This talk is going to take place this Friday, Mar. 01, from 4pm to 5pm(UTC+8, Beijing time).

[Title]
On the Wadge degrees of Borel partitions
[Abstract]
In descriptive set theory, there are a lot of semi-well-ordered hierarchies, such as the Borel hierarchy, the projective hierarchy, and the difference hierarchy. Under AD, their ultimate refinement is provided by the Wadge degrees, which is also semi-well-ordered.
Now, the question arises: what exactly gives rise to this semi-well-ordered structure?
Our goal is to reveal the true structure behind this semi-well-order. To achieve this, it is crucial to handle not subsets (two-valued functions) but partitions (k-valued functions). As long as we only observe two-valued functions, all dynamic mechanisms lurking behind collapse, appearing to our eyes only as a semi-well-order. By dealing with partitions, we can expose the ultimate dynamic structure that was concealed. What existed there is not a semi-well-order but rather a better quasi-order, -- a sort of transfinite "matryoshkas" of trees.

_____________________________________________________________________________________________________

Title ：The 45th Nankai Logic Colloquium --Takayuki Kihara

Time ：16:00pm, Mar. 1, 2024(Beijing Time)

Zoom Number ： 776 677 2207

Passcode ：477893

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## Cross-Alps Logic Seminar (speaker: Simon Henry)

Cross-Alps Logic Seminar

2/26/2024 5:36:45

On Friday 01.03.2024 at 16.00 CET

**Simon Henry** (University of Ottawa)

will give a talk on

*Higher categorical language*

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 2022 'Models, Sets and Classifications'.

All the best,

Vincenzo

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/25/2024 22:25:00

This Week in Logic at CUNY:

- - - - Monday, Feb 26, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, Feb 26, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Matteo Plebani (Turin).

Title: Semantic paradoxes as collective tragedies

Abstract: What does it mean to solve a paradox? A common assumption is that to solve a paradox we need to find the wrong step in a certain piece of reasoning. In this talk, I will argue while in the case of some paradoxes such an assumption might be correct, in the case of paradoxes such as the liar and Curry’s paradox it can be questioned.

- - - - Tuesday, Feb 27, 2024 - - - -

MOPA

CUNY Graduate Center

Tuesday, Feb 27, 1pm

Elliot Glazer Harvard University

Computational Logic Seminar

Spring 2024 (online)

Tuesday, February 27, 2:00 - 4:00 PM

For a ZOOM link contact Sergei Artemov (

sartemov@gc.cuny.edu)

Speaker: Vincent Peluce, Graduate Center

Title: What is Intuitionistic Arithmetic

Abstract: L.E.J. Brouwer famously took the subject’s intuition of time to be foundational and from there ventured to build up mathematics. Despite being largely critical of formal methods, Brouwer valued axiomatic systems for their use in both communication and memory. Through the Dutch Mathematical Society, Gerrit Mannoury posed a challenge in 1927 to provide an axiomatization of intuitionistic arithmetic. Arend Heyting’s 1928 axiomatization was chosen as the winner and has since enjoyed the status of being the de facto formalization of intuitionistic arithmetic. We argue that axiomatizations of intuitionistic arithmetic ought to make explicit the role of the subject’s activity in the intuitionistic arithmetical process. While Heyting Arithmetic is useful when we want to contrast constructed objects with platonistic ones, Heyting Arithmetic omits the contribution of the subject and thus falls short as a response to Mannoury’s challenge. We offer our own solution, Doxastic Heyting Arithmetic, or DHA, which we contend axiomatizes Brouwerian intuitionistic arithmetic

Speaker: ** Astra Kolomatskaia, Stony Brook.**

Date and Time: ** Wednesday February 28, 2024, 7:00 - 8:30 PM. IN PERSON TALK! ****Room 6417**

Title:** Displayed Type Theory and Semi-Simplicial Types.**

Abstract: One way to think about the language of Homotopy Type Theory [HoTT], is that it enforces that anything you can say is "up to homotopy". In particular, equality proofs are not strict, but rather carry the data of a particular [class of] deformation. In HoTT, all types have the structure of an infinity groupoid, and thus the language allows for conveniently working with certain infinitary structures synthetically. However, one of the most important and long standing open problems in the field is to analytically define infinitary structures such as semi-simplicial types [i.e. semi-simplicial sets "valued in" homotopy types]. The primary difficulty with this has been that as soon as you use the equality symbol in an attempted definition of such a structure, you fall into a pit of higher coherence issues such that infinitely many layers of higher coherences, with each depending on the proofs of all of the prior ones and growing exponentially in complexity, become required. In HoTT, therefore, one comes directly face-to-face with the core problems of homotopy coherent mathematics.

In this talk, we will construct semi-simplicial types in Displayed Type Theory [dTT], a fully semantically general homotopy type theory. Many of our main results are independent of type theory and will say something new and surprising about the homotopy theoretic notion of a classifier for semi-simplicial objects.

- - - - Thursday, Feb 29, 2024 - - - -

- - - - Friday, Mar 1, 2024 - - - -

Model Theory Seminar

CUNY Graduate Center

Friday Mar 1, 12:30pm NY time, Room: 6495

Rehana Patel Wesleyan University

I will present a transfer principle in structural Ramsey theory from finite structures to ultraproducts. In joint work with Bartosova, Dzamonja and Scow, we show that under certain mild conditions and assuming CH, when a class of finite structures has finite small Ramsey degrees, the ultraproduct has finite big Ramsey degrees for internal colorings. All Ramsey-theoretic definitions will be provided, and if time permits, I will give a sketch of the proof.

Logic Workshop

CUNY Graduate Center

Friday Mar 1, 2:00pm-3:30pm, Room 5417

Alf Dolich, CUNY

**Component Closed Structures on the Reals**

A structure, R, expanding (R,<) is called component closed if whenever X⊆Rn is definable so are all of X's connected components. Two basic examples of component closed structures are (R,<,+,⋅) and (R,<,⋅,Z). It turns out that these two structures are exemplary of a general phenomenon for component closed structures from a broad class of expansions of (R,<): either their definable sets are very 'tame' (as in the case of the real closed field) or they are quite 'wild' (as in the case of the real field expanded by the integers).

Next Week in Logic at CUNY:

- - - - Monday, Mar 4, 2024 - - - -

Rutgers Logic Seminar

Monday, March 4, 3:30pm, Rutgers University, Hill 705

Sean Cox, Virginia Commonwealth

Logic and Metaphysics Workshop

Date: Monday, March 4, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Elise Crull (CUNY).

Title: Declaring no dependence

Abstract: Viable fundamental ontologies require at least one suitably stable, generic-yet-toothy metaphysical dependence relation to establish fundamentality. In this talk I argue that recent experiments in quantum physics using Page-Wootters devices to model global vs. local dynamics cast serious doubt on the existence of such metaphysical dependence relations when – and arguably, inevitably within any ontological framework – physical systems serve as the relata.

- - - - Tuesday, Mar 5, 2024 - - - -

MOPA (Models of Peano Arithmetic)

CUNY Graduate Center

Tuesday, March 5, 1pm

Piotr Gruza University of Warsaw

- - - - Wednesday, Mar 6, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Jean-Pierre Marquis, Universite de Montreal.**

Date and Time: ** Wednesday March 6, 2024, 7:00 - 8:30 PM. IN PERSON TALK!**

Title:** Hom sweet Hom: a sketch of the history of duality in category theory.**

Abstract: Duality, in its various forms and roles, played a surprisingly important part in the development of category theory. In this talk, I will concentrate on the development of these forms and roles that lead to the categorical formulation of Stone-type dualities in the 1970s. I will emphasize the epistemological gain and loss along the way.

- - - - Thursday, Mar 7, 2024 - - - -

- - - - Friday, Mar 8, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, March 8, 12:30pm NY time

Virtual: Please email Victoria Gitman (

vgitman@gmail.com) for meeting id.

Jonathan Osinski University of Hamburg

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Groups, Logic, and Dynamics

This is the second installment of the meeting in Groups, Logic and Dynamics. We will be meeting in New Brunswick at the beginning of the spring season.

WHERE: Rutgers, The State University of New Jersey.

WHEN: Saturday, March 23

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

2/25/2024 12:23:35

Dear all,
The seminar meets on Wednesday February 28th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Pavel Pudlák -- Colorings of $k$-sets with low discrepancy on
small sets
Joint result with Vojtech Rodl
According to Ramsey theorem, for every $k$ and $n$, if $N$ is
sufficiently large, then for every 2-coloring $\psi$ of $k$-element
subsets of $[N]$ there exists a monochromatic set $S\sub[N]$ (a set such
that all $k$-element subsets of $S$ have the same color given by
$\psi$), $|S|=m$. The least such number is denoted by $R_k(m)$. Old
results of Erd\H os, Hajnal and Rado (1965) imply that $R_k(m)\leq {\rm
tw}_{k}(c m)$, where $\tw_k(x)$ is the tower function defined by ${\rm
tw}_1(x)=x$ and ${\rm tw}_{i+1}(x)=2^{{\rm tw}_i(x)}$. On the other
hand, these authors also showed that if $N\leq {\rm tw}_{k-1}(c'm^2)$,
then there exists a coloring~$\psi$ such that there is no monochromatic
$S\sub[N]$, $|S|=m$.
We are interested in the question what more one can say when $N$ is
smaller than ${\rm tw}_{k-1}(m)$ and $m$ is only slightly larger than
$k$. We will show that, for particular values of the parameters $k,m,N$,
there are colorings such that on all subsets $S$, $|S|\geq m$, the
number of $k$-subsets of one color is close to the number of $k$-subsets
of the other color.
Best,
David

## 44th Nankai Logic Colloquium

Nankai Logic Colloquium

2/21/2024 22:15:22

Hello everyone,

Happy Chinese New Year, Nankai Logic Colloquium is resuming for the new semester!

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

Our speaker this week will be Clark Lyons from the University of California, Los Angeles. This talk is going to take place this Friday, Feb 23, from 9am to 10am(UTC+8, Beijing time).

Title: Baire Measurable Matchings in Non-amenable Graphs
Abstract: Tutte's theorem provides a necessary and sufficient condition
for a finite graph to have a perfect matching. In this talk I will
present joint work with Kastner showing that if a locally finite Borel
graph satisfies a strengthened form of Tutte's condition, then it has a
perfect matching which is Baire measurable. As a consequence, the
Schreier graph of a free action of a non-amenable group on a Polish
space admits a Baire measurable perfect matching. This is analogous to
the result of Csoka and Lippner on factor of IID perfect matchings for
non-amenable Cayley graphs.

_____________________________________________________________________________________________________

Title ：The 44th Nankai Logic Colloquium --Clark Lyons

Time ：9:00am, Feb. 23, 2024(Beijing Time)

Zoom Number ： 776 677 2207

Passcode ：477893

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## Set theory and topology seminar 27.02.2024 Grzegorz Plebanek

Wrocław Set Theory Seminar

2/20/2024 14:46:02

I am happy to announce that at the seminar in set theory and topology (on Tuesday 27.02.2024 at 17:15 in room A.4.1 C-19** ** (Wrocław University of Science and Technology) the lecture:

"Aftermath of the Winter School"

**Grzegorz Plebanek**

Abstract:

We shall discuss two problems on measures on compact spaces posed by Jiri Spurny.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room A.4.1.A in C-19.

## Wednesday seminar

Prague Set Theory Seminar

2/19/2024 5:14:01

Dear all,
The seminar meets on Wednesday February 21st at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Jonathan Cancino Manriquez -- Preserving independent families
We will review some classical facts about the preservation of
independent families and facts related to the side by side Sacks model.
Best,
David

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/18/2024 22:38:00

This Week in Logic at CUNY:

- - - - Monday, Feb 19, 2024 - - - -

Rutgers Logic Seminar

Monday, Feb 19, 3:30pm, Rutgers University, Hill 705

Artem Chernikov, Maryland

Intersecting sets in probability spaces and Shelah's classification

Abstract: For any fixed n and e > 0, given a sufficiently long sequence of events in a probability space all of measure at least e, some n of them will have a common intersection. This follows from the inclusion-exclusion principle. A more subtle pattern: for any 0 < p < q < 1, we can't find events A_i and B_i so that the measure of A_i intersected B_j is less that p and of A_j intersected B_i is greater than q for all 1 < i < j < n, assuming n is sufficiently large. This is closely connected to a fundamental model-theoretic property of probability algebras called stability. We will discuss these and more complicated patterns that arise when our events are indexed by multiple indices. In particular, how such results are connected to higher arity generalizations of de Finetti's theorem in probability, structural Ramsey theory, hypergraph regularity in combinatorics, and model theory (no prior knowledge is expected - all of these will be introduced).

- - - - Tuesday, Feb 20, 2024 - - - -

**Computational Logic Seminar **

**Spring 2024 ****(online)**

**Tuesday, February 20 **** **

**Time 2:00 - 4:00 PM **

zoom link:

**Speaker**: *Matteo Plebani*, *The University of Turin*

**Title:** *Counterpossibles in relative computability theory: a closer look*

**Abstract: **A counterpossible is a counterfactual with an impossible antecedent, like “if zero were equal to one, two would be equal to five”. Matthias Jenny [Jenny, 2018] has argued that the following is an example of a false counterpossible:

HT If the validity problem were algorithmically solvable, then arithmetical truth would be also algorithmically decidable

As Jenny himself emphasizes, establishing that HT is a false counterpossible would be highly significant. According to the standard analysis of counterfactuals ([Lewis, 1973], [Stalnaker, 1968]) all counterpossibles are vacuously true. If HT is false, then, the standard analysis of counterfactuals is wrong.

In this paper, we will argue that HT admits two readings, which are expressed by two different ways of formalizing HT. Under the first reading, HT is clearly a counterpossible. Under the second reading, HT is clearly false. Hence, it is possible to read HT as a counterpossible (section 2) and it is possible to read HT as a false claim (section 3). However, it is unclear that it is possible to do both things at once, i.e. interpret HT as a false counterpossible.

It can be proven that the two readings are not equivalent. The formalization expressing the first reading is a mathematical theorem, which means that under the first reading, HT is a true counterpossible. On the other hand, I will argue that under the second reading HT, while false, is best interpreted as a counterpossible with a contingent antecedent.

- - - - Wednesday, Feb 21, 2024 - - - -

- - - - Thursday, Feb 22, 2024 - - - -

- - - - Friday, Feb 23, 2024 - - - -

Logic Workshop

CUNY Graduate Center

Friday Feb 23, 2:00pm-3:30pm, Room 5417

Tom Benhamou Rutgers University

**Commutativity of cofinal types of ultrafilters**

The Tukey order finds its origins in the concept of Moore-Smith convergence in topology, and is especially important when restricted to ultrafilters with reverse inclusion. The Tukey order of ultrafilters over ω was studied intensively by Blass, Dobrinen, Isbell, Raghavan, Shelah, Todorcevic and many others, but still contains many fundamental unresolved problems. After reviewing the topological background for the Tukey order, I will present a recent development in the theory of the Tukey order restricted to ultrafilters on measurable cardinals, and explain how different the situation is when compared to ultrafilters on ω. Moreover, we will see an important application to the Galvin property of ultrafilters. In the second part of the talk, we will demonstrate how ideas and intuition from ultrafilters over measurable cardinals lead to new results on the Tukey order restricted to ultrafilters over ω. This is joint with Natasha Dobrinen.

Next Week in Logic at CUNY:

- - - - Monday, Feb 26, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, Feb 26, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Matteo Plebani (Turin).

Title: Semantic paradoxes as collective tragedies

Abstract: What does it mean to solve a paradox? A common assumption is that to solve a paradox we need to find the wrong step in a certain piece of reasoning. In this talk, I will argue while in the case of some paradoxes such an assumption might be correct, in the case of paradoxes such as the liar and Curry’s paradox it can be questioned.

- - - - Tuesday, Feb 27, 2024 - - - -

MOPA

CUNY Graduate Center

Tuesday, Feb 27, 1pm

Elliot Glazer Harvard University

- - - - Wednesday, Feb 28, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Astra Kolomatskaia, Stony Brook.**

Date and Time: ** Wednesday February 28, 2024, 7:00 - 8:30 PM. IN PERSON TALK! ****Room 6417**

Title:** Displayed Type Theory and Semi-Simplicial Types.**

Abstract: One way to think about the language of Homotopy Type Theory [HoTT], is that it enforces that anything you can say is "up to homotopy". In particular, equality proofs are not strict, but rather carry the data of a particular [class of] deformation. In HoTT, all types have the structure of an infinity groupoid, and thus the language allows for conveniently working with certain infinitary structures synthetically. However, one of the most important and long standing open problems in the field is to analytically define infinitary structures such as semi-simplicial types [i.e. semi-simplicial sets "valued in" homotopy types]. The primary difficulty with this has been that as soon as you use the equality symbol in an attempted definition of such a structure, you fall into a pit of higher coherence issues such that infinitely many layers of higher coherences, with each depending on the proofs of all of the prior ones and growing exponentially in complexity, become required. In HoTT, therefore, one comes directly face-to-face with the core problems of homotopy coherent mathematics.

In this talk, we will construct semi-simplicial types in Displayed Type Theory [dTT], a fully semantically general homotopy type theory. Many of our main results are independent of type theory and will say something new and surprising about the homotopy theoretic notion of a classifier for semi-simplicial objects.

This talk is based on joint work with Michael Shulman. Reference: https://arxiv.org/abs/2311.18781

- - - - Thursday, Feb 29, 2024 - - - -

- - - - Friday, Mar 1, 2024 - - - -

Model Theory Seminar

CUNY Graduate Center

Friday Mar 1, 12:30pm NY time, Room: 6495

Rehana Patel Wesleyan University

Logic Workshop

CUNY Graduate Center

Friday Mar 1, 2:00pm-3:30pm, Room 5417

Alf Dolich, CUNY

**Component Closed Structures on the Reals**

A structure, R, expanding (R,<) is called component closed if whenever X⊆Rn is definable so are all of X's connected components. Two basic examples of component closed structures are (R,<,+,⋅) and (R,<,⋅,Z). It turns out that these two structures are exemplary of a general phenomenon for component closed structures from a broad class of expansions of (R,<): either their definable sets are very 'tame' (as in the case of the real closed field) or they are quite 'wild' (as in the case of the real field expanded by the integers).

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Groups, Logic, and Dynamics

This is the second installment of the meeting in Groups, Logic and Dynamics. We will be meeting in New Brunswick at the beginning of the spring season.

WHERE: Rutgers, The State University of New Jersey.

WHEN: Saturday, March 23

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Logic Seminar Wed 21.02.2024 17:00 hrs at NUS by Neil Barton

NUS Logic Seminar

2/18/2024 18:47:25

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 21 February 2024, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Neil Barton
Title: Title: Potentialist Sets, Intensions, and Non-Classicality
A popular view in the philosophy of set theory is that of *potentialism*:
the position that the set-theoretic universe unfolds as more sets come
into existence or become accessible to us. This often gets formalised
using *modal logic*, but there is always a question of how to move to
*non-modal* theories. In this latter regard, a difficult question for
the potentialist is to explain how *intensional entities* (entities
individuated by an application condition rather than an extension) behave,
and in particular what logic governs them. This talk will discuss some
work in progress on this issue. We'll see how to motivate acceptance of
different propositional logics for different flavours of potentialism,
and discuss the prospects for proving results about the kinds of
first-order theories validated.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/11/2024 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Feb 12, 2024 - - - -

Rutgers Logic Seminar

Monday, Feb 12, 3:30pm, Rutgers University, Hill 705

Gunter Fuchs, CUNY

Blurry HOD: a hierarchy of inner models

For a cardinal $\kappa\ge 2$, one can weaken the classical concept "x is ordinal definable" (i.e., x is the unique object satisfying some condition involving ordinal parameters) to "x is <$\kappa$-blurrily ordinal definable," meaning that x is one of fewer than $\kappa$ many objects satisfying some condition involving ordinal parameters. By considering the hereditary version of this, one naturally arrives at the inner model <$\kappa$-HOD, the class of all hereditarily <$\kappa$-blurrily ordinal definable sets. In ZFC, by varying $\kappa$, one obtains a hierarchy of inner models spanning the entire spectrum from HOD to V. Those stages in the hierarchy where something new is added I call leaps.

I will give an overview of what is known about this hierarchy: ZFC-provable facts regarding the relationships between the stages of the hierarchy and the basic structure of leaps, and consistency results on leap constellations, including consistency strength determinations.

- - - - Tuesday, Feb 13, 2024 - - - -

MOPA

CUNY Graduate Center

Tuesday, Feb 13, 1pm

Dino Rossegger TU WienThe Borel complexity of first-order theories

The Borel hierarchy gives a robust way to stratify the complexity of sets of countable structures and is intimately tied with definability in infinitary logic via the Lopez-Escobar theorem. However, what happens with sets axiomatizable in finitary first-order logic, such as the set of structures satisfying a given finitary first-order theory T? Is the complexity of the set of T's models in any way related to the quantifier complexity of the sentences axiomatizing it? In particular, if a theory T is not axiomatizable by a set of sentences of bounded quantifier complexity, can the set of models of T still be at a finite level of the Borel hierarchy?

In this talk, we will present results concerning these questions:

In joint work with Andrews, Gonzalez, Lempp, and Zhu we show that the set of models of a theory T is Π0ω-complete if and only if T does not have an axiomatization by sentences of bounded quantifier complexity, answering the last question in the negative. We also characterize the Borel complexity of the set of models of complete theories in terms of their finitary axiomatizations. Our results suggest that infinitary logic does not provide any efficacy when defining first-order properties, a phenomenon already observed by Wadge and Keisler and, recently, rediscovered by Harrison-Trainor and Kretschmer using different techniques.

Combining our results with recent results by Enayat and Visser, we obtain that a large class of theories studied in the foundations of mathematics, sequential theories, have a maximal complicated set of models.

**Computational Logic Seminar **

**Spring 2024 ****(online)**

**Tuesday, February 13 **** **

**Speaker**: Melvin Fitting, CUNY Graduate Center

**Title:** *About Semantic Tableaus*

**Abstract:**I will sketch the basics of tableau proof systems, beginning with those for classical propositional logic. Then I will move to intuitionistic tableaus and modal tableaus (more than one kind of tableau system). Finally I’ll say something about quantifiers. Slides exist for the beginning part of the talk. When they run out I’ll work on the Zoom equivalent of a blackboard.

- - - - Wednesday, Feb 14, 2024 - - - -

- - - - Thursday, Feb 15, 2024 - - - -

- - - - Friday, Feb 16, 2024 - - - -

Computability Seminar

CUNY Graduate Center

Friday, Feb 16, 10:30-11:30am NY time, Room: 3305

Speaker: Andrea Volpi, University of Udine

**Largeness notions**

Finite Ramsey Theorem states that fixed n,m,k∈N, there exists N∈N such that for each coloring of [N]n with k colors, there is a homogeneous subset H of N of cardinality at least m. Starting with the celebrated Paris-Harrington theorem, many Ramsey-like results have been studied using different largeness notions rather than the cardinality. I will introduce the largeness notion defined by Ketonen and Solovay based on fundamental sequences of ordinals. Then I will describe an alternative and more flexible largeness notion using blocks and barriers. If time allows, I will talk about how the latter can be used to study a more general Ramsey-like result.

Logic Workshop

CUNY Graduate Center

Friday Feb 16, 2:00pm-3:30pm, Room 5417

Damir Dzhafarov, University of Connecticut

**The Ginsburg-Sands theorem and computability**

In their 1979 paper `Minimal Infinite Topological Spaces,’ Ginsburg and Sands proved that every infinite topological space has an infinite subspace homeomorphic to exactly one of the following five topologies on ω: indiscrete, discrete, initial segment, final segment, and cofinite. The proof, while nonconstructive, features an interesting application of Ramsey's theorem for pairs (RT22). We analyze this principle in computability theory and reverse mathematics, using Dorais's formalization of CSC spaces. Among our results are that the Ginsburg-Sands theorem for CSC spaces is equivalent to ACA0, while for Hausdorff spaces it is provable in RCA0. Furthermore, if we enrich a CSC space by adding the closure operator on points, then the Ginsburg-Sands theorem turns out to be equivalent to the Chain-Antichain Principle (CAC). The most surprising case is that of the Ginsburg-Sands theorem restricted to T1 spaces. Here, we show that the principle lies strictly between ACA0 and RT22, yielding perhaps the first natural theorem of ordinary mathematics (i.e., conceived outside of logic) to occupy this interval. I will discuss the proofs of both the implications and separations, which feature several novel combinatorial elements, and survey a new class of purely combinatorial principles below ACA0 and not implied by RT22 revealed by our investigation. This is joint work with Heidi Benham, Andrew DeLapo, Reed Solomon, and Java Darleen Villano.

Next Week in Logic at CUNY:

- - - - Monday, Feb 19, 2024 - - - -

- - - - Tuesday, Feb 20, 2024 - - - -

- - - - Wednesday, Feb 21, 2024 - - - -

- - - - Thursday, Feb 22, 2024 - - - -

- - - - Friday, Feb 23, 2024 - - - -

Logic Workshop

CUNY Graduate Center

Friday Feb 23, 2:00pm-3:30pm, Room 5417

Tom Benhamou Rutgers University

- - - - Other Logic News - - - -

CONFERENCE ANNOUNCEMENT

Groups, Logic, and Dynamics

This is the second installment of the meeting in Groups, Logic and Dynamics. We will be meeting in New Brunswick at the beginning of the spring season.

WHERE: Rutgers, The State University of New Jersey.

WHEN: Saturday, March 23

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

2/10/2024 6:25:52

Dear all,
The seminar meets on Wednesday February 14th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
The program is not yet determined, the backup option is Chris and/or
Šárka talking about Kurepa trees.
Best,
David

## Logic Seminar Talk 7 February 2024 17:00 hrs by Alexander Rabinovich at NUS

NUS Logic Seminar

2/6/2024 0:43:32

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 7 February 2024, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Alexander Rabinovich, Tel Aviv University
Title: The Church Synthesis Problem over Continuous Time
Abstract:
Church's Problem asks for the construction of a procedure which, given a
logical specification S(I,O) between input-strings I and
output-strings O, determines whether there exists an operator F that
implements the specification in the sense that S(I,F(I)) holds for all
inputs I. Buechi and Landweber gave a procedure to solve Church's
problem for MSO specifications and operators computable by finite-state
automata. We investigate a generalization of the Church synthesis
problem to the continuous time of the non-negative reals. It turns out
that in the continuous time there are phenomena which are very different
from the canonical discrete time domain of the natural numbers.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## This Week in Logic at CUNY

This Week in Logic at CUNY

2/4/2024 22:38:00

This Week in Logic at CUNY:

- - - - Monday, Feb 5, 2024 - - - -

Rutgers Logic Seminar

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

Filippo Calderoni, Rutgers

The L-space conjecture and descriptive set theory

Logic and Metaphysics Workshop

Date: Monday, Feb 5, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

Roman Kossak, CUNY

*Title*: Some model theory for axiomatic theories of truth

*Abstract*: Tarski’s arithmetic is the complete theory of (N,+,x,Tr), where (N,+,x) is the standard model of arithmetic and Tr is the set of Gödel numbers of all true arithmetic sentences. An axiomatic theory of truth is an axiomatic subtheory of Tarski’s arithmetic. If (M,+,x,T) is a model of an axiomatic theory of truth, then we call T a truth class. In 1981, Kotlarski, Krajewski, and Lachlan proved that every completion of Peano’s arithmetic has a model that is expandable to a model with a truth class T that satisfies all biconditionals in Tarski’s definition of truth formalized in PA. If T is such a truth class, it assigns truth values to all sentences in the sense of M, standard and nonstandard. The proof showed that such truth classes can be quite pathological. For example, they may declare true some infinite disjunctions of the single sentence (0=1). In 2018, Enayat and Visser gave a much simplified model-theoretic proof, which opened the door for further investigations of nonstandard truths, and many interesting new results by many authors appeared. I will survey some of them, concentrating on their model-theoretic content.

- - - - Tuesday, Feb 6, 2024 - - - -

- - - - Wednesday, Feb 7, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Saeed Salehi, Univeristy of Tarbiz.**

Date and Time: ** Wednesday February 7, 2024, 11:00AM - 12:00 NOON. NOTICE SPECIAL TIME!!! ZOOM TALK!!! (see website for zoom link)**

Title:** On Chaitin's two HP's: (1) Heuristic Principle and (2) Halting Probability.**

Abstract: Two important achievements of Chaitin will be investigated: the Omega number, which is claimed to be the halting probability of input-free programs, and the heuristic principle, which is claimed to hold for program-size complexity. Chaitin's heuristic principle says that the theories cannot prove the heavier sentences; the sentences and the theories were supposedly weighed by various computational complexities, which all turned out to be wrong or incomplete. In this talk, we will introduce a weighting that is not based on any computational complexity but on the provability power of the theories, for which Chaitin's heuristic principle holds true. Also, we will show that the Omega number is not equal to the halting probability of the input-free programs and will suggest some methods for calculating this probability, if any.

- - - - Thursday, Feb 8, 2024 - - - -

- - - - Friday, Feb 9, 2024 - - - -

Computability Seminar

CUNY Graduate Center

Friday, Feb 9, 10:30-11:30am NY time, Room: 3305

Title: Computability of equilibrium measures

Speaker: Emma Dinowitz, Grad Center

Set Theory Seminar

CUNY Graduate Center

Friday, Feb 9, 12:30pm NY time, Room: 6494

Tom Benhamou Rutgers University

**Tukey-top ultrafilters under UA**

In the first part of the talk, we will provide some background and motivation to study the Glavin property. In particular, we will present a recently discovered connection between the Galvin property and the Tukey order on ultrafilters. This is a joint result with Natasha Dobrinen. In the second part, we will introduce several diamond-like principles for ultrafilters, and prove some relations with the Galvin property. Finally, we use the Ultrapower Axiom to characterize the Galvin property in the known canonical inner models. The second and third part is joint work with Gabriel Goldberg.

Logic Workshop

CUNY Graduate Center

Friday Feb 9, 2:00pm-3:30pm, Room 5417

Russell Miller CUNY

**Properties of Generic Algebraic Fields**

The algebraic field extensions of the rational numbers Q – equivalently, the subfields of the algebraic closure ¯¯¯¯Q – naturally form a topological space homeomorphic to Cantor space. Consequently, one can speak of 'large' collections of such fields, in the sense of Baire category: collections that are comeager in the space. Under a standard definition, the *1-generic fields* form a comeager set in this space. Therefore, one may think of a property common to all 1-generic fields as a property that one might reasonably expect to be true of an arbitrarily chosen algebraic field.

We will present joint work with Eisenträger, Springer, and Westrick that proves several intriguing properties to be true of all 1-generic fields F. First, in every such F, both the subring Z of the integers and the subring OF of the algebraic integers of F cannot be defined within F by an existential formula, nor by a universal formula. (Subsequent work by Dittman and Fehm has shown that in fact these subrings are completely undefinable in these fields.) Next, for every presentation of every such F, the *root set*

RF={p∈Z[X]:p(X)=0 has a solution in F}

is always of low Turing degree relative to that presentation, but is essentially always undecidable relative to the presentation. Moreover, the set known as *Hilbert's Tenth Problem for F*,

HTP(F)={p∈Z[X1,X2,…]:p(X1,…,Xn)=0 has a solution in Fn},

is exactly as difficult as RF, which is its restriction to single-variable polynomials. Finally, even the question of having infinitely many solutions,

{p∈Z[X1,X2,…]:p(→X)=0 has infinitely many solutions in Fn},

is only as difficult as RF. These results are proven by using a forcing notion on the fields and showing that it is decidable whether or not a given condition forces a given polynomial to have a root, or to have infinitely many roots.

Next Week in Logic at CUNY:

- - - - Monday, Feb 12, 2024 - - - -

Rutgers Logic Seminar

Monday, Feb 12, 3:30pm, Rutgers University, Hill 705

Gunter Fuchs, CUNY

- - - - Tuesday, Feb 13, 2024 - - - -

MOPA

CUNY Graduate Center

Tuesday, Feb 13, 1pm

Dino Rossegger TU WienThe Borel complexity of first-order theories

The Borel hierarchy gives a robust way to stratify the complexity of sets of countable structures and is intimately tied with definability in infinitary logic via the Lopez-Escobar theorem. However, what happens with sets axiomatizable in finitary first-order logic, such as the set of structures satisfying a given finitary first-order theory T? Is the complexity of the set of T's models in any way related to the quantifier complexity of the sentences axiomatizing it? In particular, if a theory T is not axiomatizable by a set of sentences of bounded quantifier complexity, can the set of models of T still be at a finite level of the Borel hierarchy?

In this talk, we will present results concerning these questions:

In joint work with Andrews, Gonzalez, Lempp, and Zhu we show that the set of models of a theory T is Π0ω-complete if and only if T does not have an axiomatization by sentences of bounded quantifier complexity, answering the last question in the negative. We also characterize the Borel complexity of the set of models of complete theories in terms of their finitary axiomatizations. Our results suggest that infinitary logic does not provide any efficacy when defining first-order properties, a phenomenon already observed by Wadge and Keisler and, recently, rediscovered by Harrison-Trainor and Kretschmer using different techniques.

Combining our results with recent results by Enayat and Visser, we obtain that a large class of theories studied in the foundations of mathematics, sequential theories, have a maximal complicated set of models.

- - - - Wednesday, Feb 14, 2024 - - - -

- - - - Thursday, Feb 15, 2024 - - - -

- - - - Friday, Feb 16, 2024 - - - -

Computability Seminar

CUNY Graduate Center

Friday, Feb 16, 10:30-11:30am NY time, Room: 3305

Speaker: Andrea Volpi, University of Udine

**Largeness notions**

Finite Ramsey Theorem states that fixed n,m,k∈N, there exists N∈N such that for each coloring of [N]n with k colors, there is a homogeneous subset H of N of cardinality at least m. Starting with the celebrated Paris-Harrington theorem, many Ramsey-like results have been studied using different largeness notions rather than the cardinality. I will introduce the largeness notion defined by Ketonen and Solovay based on fundamental sequences of ordinals. Then I will describe an alternative and more flexible largeness notion using blocks and barriers. If time allows, I will talk about how the latter can be used to study a more general Ramsey-like result.

Logic Workshop

CUNY Graduate Center

Friday Feb 16, 2:00pm-3:30pm, Room 5417

Damir Dzhafarov, University of Connecticut

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

2/3/2024 7:21:06

Dear all,
There is no seminar on Wednesday next week.
However, we have Andy Zucker visiting the Institute during the next
week, Andy will give a talk at the Set Theory and Analysis seminar on
Tuesday morning 10:00--11:30, Institute of Mathematics CAS, Zitna 25,
konirna room, ground floor, front building.
Program: Andy Zucker -- Ultracoproducts and weak containment for flows
of topological groups
We develop the theory of ultracoproducts and weak containment for flows
of arbitrary topological groups. This provides a nice complement to
corresponding theories for p.m.p. actions and unitary representations of
locally compact groups. For the class of locally Roelcke precompact
groups, the theory is especially rich, allowing us to define for certain
families of G-flows a suitable compact space of weak types. When G is
locally compact, all G-flows belong to one such family, yielding a
single compact space describing all weak types of G-flows.
Best,
David

## This Week in Logic at CUNY

This Week in Logic at CUNY

1/28/2024 22:30:00

This Week in Logic at CUNY:

- - - - Monday, Jan 29, 2024 - - - -

Rutgers Logic Seminar

Monday, Jan 29, 3:30pm, Rutgers University, Hill 705

Jenna Zomback, Maryland

Boundary actions of free semigroups

- - - - Tuesday, Jan 30, 2024 - - - -

- - - - Wednesday, Jan 31, 2024 - - - -

- - - - Thursday, Feb 1, 2024 - - - -

- - - - Friday, Feb 2, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, Feb 2, 12:30pm NY time, Room: 6494

Dima Sinapova Rutgers University

Logic Workshop

CUNY Graduate Center

Friday Feb 2, 2:00pm-3:30pm, Room 5417

Gunter Fuchs CUNY

TBA

Next Week in Logic at CUNY:

- - - - Monday, Feb 5, 2024 - - - -

Logic and Metaphysics Workshop

Date: Monday, Feb 5, 4.15-6.15pm (NY time)

Room: Graduate Center Room 7395

*Title*: Some model theory for axiomatic theories of truth

*Abstract*: Tarski’s arithmetic is the complete theory of (N,+,x,Tr), where (N,+,x) is the standard model of arithmetic and Tr is the set of Gödel numbers of all true arithmetic sentences. An axiomatic theory of truth is an axiomatic subtheory of Tarski’s arithmetic. If (M,+,x,T) is a model of an axiomatic theory of truth, then we call T a truth class. In 1981, Kotlarski, Krajewski, and Lachlan proved that every completion of Peano’s arithmetic has a model that is expandable to a model with a truth class T that satisfies all biconditionals in Tarski’s definition of truth formalized in PA. If T is such a truth class, it assigns truth values to all sentences in the sense of M, standard and nonstandard. The proof showed that such truth classes can be quite pathological. For example, they may declare true some infinite disjunctions of the single sentence (0=1). In 2018, Enayat and Visser gave a much simplified model-theoretic proof, which opened the door for further investigations of nonstandard truths, and many interesting new results by many authors appeared. I will survey some of them, concentrating on their model-theoretic content.

- - - - Tuesday, Feb 6, 2024 - - - -

- - - - Wednesday, Feb 7, 2024 - - - -

The New York City Category Theory Seminar

Department of Computer Science

Department of Mathematics

The Graduate Center of The City University of New York

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: ** Saeed Salehi, Univeristy of Tarbiz.**

Date and Time: ** Wednesday February 7, 2024, 11:00AM - 12:00 NOON. NOTICE SPECIAL TIME!!! ZOOM TALK!!! (see website for zoom link)**

Title:** On Chaitin's two HP's: (1) Heuristic Principle and (2) Halting Probability.**

Abstract: Two important achievements of Chaitin will be investigated: the Omega number, which is claimed to be the halting probability of input-free programs, and the heuristic principle, which is claimed to hold for program-size complexity. Chaitin's heuristic principle says that the theories cannot prove the heavier sentences; the sentences and the theories were supposedly weighed by various computational complexities, which all turned out to be wrong or incomplete. In this talk, we will introduce a weighting that is not based on any computational complexity but on the provability power of the theories, for which Chaitin's heuristic principle holds true. Also, we will show that the Omega number is not equal to the halting probability of the input-free programs and will suggest some methods for calculating this probability, if any.

- - - - Thursday, Feb 8, 2024 - - - -

- - - - Friday, Feb 9, 2024 - - - -

Set Theory Seminar

CUNY Graduate Center

Friday, Feb 9, 12:30pm NY time, Room: 6494

Tom Benhamou Rutgers University

Logic Workshop

CUNY Graduate Center

Friday Feb 9, 2:00pm-3:30pm, Room 5417

Russell Miller CUNY

TBA

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## 43rd Nankai Logic Colloquium

Nankai Logic Colloquium

1/24/2024 21:58:06

Hello everyone,

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

Our speaker this week will be Alexander S. Kechris from the California Institute of Technology. This talk is going to take place this Friday, Jan 26, from 9am to 10am(UTC+8, Beijing time).

Title: The compact action realization problem

Abstract:

In this talk I will discuss realizations of countable Borel equivalence relations by continuous actions of countable groups, focusing in particular on the problem of realization by continuous actions on compact spaces and more specifically subshifts. This also leads to considering a natural universal space for actions and equivalence relations via subshifts and the study of the descriptive and topological properties in this universal space of various classes of countable Borel equivalence relations, especially the hyperfinite ones.

_____________________________________________________________________________________________________

Title ：The 43rd Nankai Logic Colloquium --Alexander S. Kechris

Time ：9:00am, Jan. 26, 2024(Beijing Time)

Zoom Number ： 776 677 2207

Passcode ：477893

Link ：https://us02web.zoom.us/j/7766772207?pwd=eUtGVzBMdExhZWl6ZllRRFZaVnU2dz09&omn=85249314599

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## 7th Workshop on Generalised Baire Spaces

Conference

1/24/2024

This is the seventh in a series of workshops that have taken place from 2014. These workshops aim to connect researchers working in the descriptive set theory of Baire and Cantor spaces of functions on uncountable cardinals and its connections with infinite combinatorics and model theory. The upcoming workshop features several well-known speakers and aims to connect this area with large cardinals. There will be ample time for discussion and collaboration.

Tagged: Claudio Agostini, David Chodounský, Peter Holy, Philipp Lücke, Chris Lambie-Hanson, Luca Motto Ros, Miguel Moreno, Beatrice Pitton, Grigor Sargsyan, Farmer Schlutzenberg, Sarka Stejskalova, Dorottya Sziraki, Christopher Henney-Turner

## Invitation to Logic Seminar 31 January 2024 17:00 hrs at NUS by Yu Liang

NUS Logic Seminar

1/23/2024 2:22:23

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 31 January 2023, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Yu Liang
Title: Some Applications of Recursion Theory to Geometric Measure Theory
Abstract: Geometric measure theory relates effectivity notions
to dimensions and measures like the Hausdorff dimension.
The talk gives further links to the Axiom of Determinacy
over ZF (it is not consistent with ZFC) and how these
influence the geometry of the finite-dimensional Euclidian
Space and its subsets. The talk explains the theorems of
Besicovitch and Davis, of father and son Lutz and of Slaman;
these theorems are related to recent results in the
field including those by the speaker.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## This Week in Logic at CUNY

This Week in Logic at CUNY

1/21/2024 22:30:00

Hi everyone,

The Spring 2024 semester starts this Thursday, 1/25 -- welcome back! While many seminars will not meet this week, please take note of the special memorial event for Martin Davis on Friday 1/26.

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Jan 22, 2024 - - - -

Rutgers Logic Seminar

Monday, Dec 11, 3:30pm, Rutgers University, Hill 705

Will Boney (Texas State)

Building generalized indiscernibles in nonelementary classes with set theory

- - - - Tuesday, Jan 23, 2024 - - - -

- - - - Wednesday, Jan 24, 2024 - - - -

- - - - Thursday, Jan 25, 2024 - - - -

- - - - Friday, Jan 26, 2024 - - - -

Memorial Lectures for Martin Davis

January 26, 2024

Courant Institute

All are welcome to attend this special event in memory of Professor Martin Davis.

There will be three lectures on his work from 1:00 - 2:30 pm, a memorial for Martin

and Virginia Davis from 2:45 - 3:45 pm, and a reception afterwards from 4-6 pm.

Preregistration is requested, ideally by January 15, using the website

https://cims.nyu.edu/dynamic/conferences/davis-memorial/Next Week in Logic at CUNY:

- - - - Monday, Jan 29, 2024 - - - -

- - - - Tuesday, Jan 30, 2024 - - - -

- - - - Wednesday, Jan 31, 2024 - - - -

- - - - Thursday, Feb 1, 2024 - - - -

- - - - Friday, Feb 2, 2024 - - - -

- - - - 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

1/21/2024 3:39:49

Dear all,
The seminar meets on Wednesday January 24th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
There will be no seminar on Wednesday January 31st (Winter School) and
probably no seminar on February 7th (workshop in Bristol).
Program January 24th:
Cesar Corral -- MAD families with pseudocompact hyperspaces
Pseudocompactness of hyperspaces was studied by J. Ginsburg, who asked
whether there is a relationship between the pseudocompactness of
X^\omega and the hyperspace exp(X) for a topological space X. For an
almost disjoint family \mathcal{A}, maximality is equivalent to the
pseudocompactness of \Psi(\mathcal{A}) and that of
\Psi(\mathcal{A})^\omega. Hence J. Cao and T. Nogura asked whether
some/every MAD family has a pseudocompact hyperspace.
Recently, the statement that every MAD family has a pseudocompact
hyperspace was proved to be equivalent to the Novak or Baire number
\mathfrak{n} being greater than \mathfrak{c}, however, not much more is
known about the existence of MAD families with pseudocompact hyperspace.
We will address this problem by showing many models and cardinal
invariant assumptions that imply the existence of MAD families with
pseudocompact hyperspace.
Best,
David

## Second Wrocław Logic Conference, Wrocław, 31 May to 2 Jun, 2024

Conference

1/20/2024 16:23:50

SECOND WROCLAW LOGIC CONFERENCE will take place 31st May - 2nd June 2024, in Wrocław, Poland.
The website of the conference: https://prac.im.pwr.edu.pl/~twowlc/
There is no conference fee.
There will be two special lectures during the conference:
* Mostowski lecture, by Stevo Todorcevic,
* Ryll-Nardzewski lecture, by Jan van Mill.
Invited speakers:
Monroe Eskew (KGRC)
Rafal Filipow, University of Gdańsk
Takehiko Gappo, TU Wien
Martin Goldstern, TU Wien
Eliza Jabłońska, AGH
Ziemowit Kostana, University of Warsaw and Bar-Ilan University
Andrzej Kucharski, University of Silesia
Aleksandra Kwiatkowska, University of Wrocław & WWU Munster
Andreas Lietz, University of Munster
Matteo Viale, University of Torino
Zoltán Vidnyánszky, Eotvos University
Bartosz Wcisło, University of Gdańsk
The conference is organized by Politechnika Wrocławska and Uniwersytet Wrocławski. This is a continuation of First Gdansk Logic Conference.
Scientific Committee:
Arturo Martinez-Celis (Uniwersytet Wrocławski)
Grigor Sargsyan (Polish Academy of Sciences)
Szymon Żeberski (Politechnika Wrocławska)
Organizing Committee:
Wrocław Set Theory Group & Grigor Sargsyan

Tagged: Monroe Eskew, Rafal Filipow, Takehiko Gappo, Martin Goldstern, Eliza Jabłońska, Ziemowit Kostana, Andrzej Kucharski, Aleksandra Kwiatkowska, Andreas Lietz, Matteo Viale, Zoltán Vidnyánszky, Bartosz Wcisło

## Set Theory and Topology Seminar 23.01.2024 Łukasz Mazurkiewicz

Wrocław Set Theory Seminar

1/19/2024 16:23:50

I am happy to announce that at the seminar in Set Theory and Topology on Tuesday 23.01.2024 at 17:15 in room 601 (Mathematical Institute, University of Wrocław) the lecture:

"Analytic families of trees"

will be presented by

**Łukasz Mazurkiewicz**

Abstract.

Every tree can be seen as a point in a space P(2^<\omega) or P(\omega^<\omega). Therefore, families of trees are subsets of these "incarnations" of Cantor space and, as such, can be analyzed from the perspective of descriptive complexity. In this talk I would like to explore some classical families of trees with some focus put on the ones, which are analytic complete.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room.

## Urgent Announcement of Nankai Logic Colloquium: change to Voov (Tencent meeting)

Nankai Logic Colloquium

1/19/2024 2:26:08

Hello everyone,

Sorry, we have changed the meeting software to Voov (Tencent meeting) because the our Zoom account has been banned.

Please download Voov (Tencent meeting) from the following link:

https://voovmeeting.com/download-center.html?from=1002

the attachment is the Manual for using Voov (Tencent meeting)

_____________________________________________________________________________________________________

Title ：The 42nd Nankai Logic Colloquium --Gianluca Paolini

Time ：16:00pm, Jan. 19, 2024(Beijing Time)

Voov (Tencent meeting) Number ： 370 658 815

Passcode ： 123456

_____________________________________________________________________

Best Wishes,

Ming Xiao

## Set Theory in the United Kingdom, London, February 15, 2024

Conference

1/20/2024 4:43:35

You are invited to attend (or zoom-into) STUK 12, Set Theory in the United Kingdom. The meeting will take place on the campus of UCL on February 15, 2024, from 11am-6pm and will be broadcast via zoom.

https://www.dpmms.cam.ac.uk/~dbl25/STUK/
Invited speakers will include:
Shaun Allison
Raiean Banerjee
Martina Ianella
The scientific organizers are Benedikt Loewe and Andrew Brooke-Taylor. The local organizer is Samuel Coskey.

Tagged: Shaun Allison, Raiean Banerjee, Martina
Ianella

## 42nd Nankai Logic Colloquium

Nankai Logic Colloquium

1/18/2024 4:43:35

Hello everyone,

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

Our speaker this week will be Gianluca Paolini from the University of Turin. This talk is going to take place this Friday, Jan 19, from 4pm to 5pm(UTC+8, Beijing time).

Title: The Isomorphism Problem for Oligomorphic Groups with Weak Elimination of Imaginaries

Abstract: In Nies et al. [JML 22 (2022)] it was asked if equality on the reals is sharp as a lower bound for the complexity of topological isomorphism between oligomorphic groups. We prove that under the assumption of weak elimination of imaginaries this is indeed the case. Our methods are model theoretic and they also have applications on the classical problem of reconstruction of isomorphisms of permutation groups from (topological) isomorphisms of automorphisms groups. As a concrete application, we give an explicit description of Aut(GL(V)) for any vector space V of dimension \aleph_0 over a finite field, in affinity with the classical description for finite dimensional spaces due to Schreier and van der Waerden.

_____________________________________________________________________________________________________

Title ：The 42nd Nankai Logic Colloquium --Gianluca Polini

Time ：16:00pm, Jan. 19, 2024(Beijing Time)

Zoom Number ： 708 354 1963

Passcode ： 477893

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## Cross-Alps Logic Seminar for World Logic Day (speaker: Charles Steinhorn)

Cross-Alps Logic Seminar

1/15/2024 2:00:00

On
Friday 19.01.2023 at 16:00

on
the occasion of World Logic Day 2024, a special session of the
Cross-Alps Logic Seminars will take place, with special guest

**Charles
Steinhorn** (Vassar College)

who
will give a talk on

**O-minimality
as a framework for tame mathematical economics**

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 2022 'Models, sets and classification'.

## Wednesday seminar

Prague Set Theory Seminar

1/14/2024 16:51:04

Dear all,
The seminar meets on Wednesday January 17th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Chris Lambie-Hanson -- Indecomposable ultrafilters and the
Proper Forcing Axiom
A common heuristic in the study of forcing axioms and compactness
principles is the following: in models of strong forcing axioms, such as
PFA, the cardinal omega_2 behaves in many ways like a strongly compact
or supercompact cardinal. For example, classical results in the study of
large cardinals imply that the Singular Cardinal Hypothesis holds, and
square principles fail, above a strongly compact cardinal. Much later,
both of these conclusions were also shown to follow from the Proper
Forcing Axiom. In this talk, we present a very recent result in this
vein. We will prove that, if PFA holds and kappa is a cardinal carrying
a uniform indecomposable ultrafilter, then kappa is either measurable or
a countable limit of measurable cardinals, providing an analogue of a
recent result of Goldberg establishing the same conclusion above a
strongly compact cardinal. This is joint work with Assaf Rinot and Jing
Zhang.
Best,
David

## Logic Seminar at NUS Wed 17.01.2024 17:00 hrs by Tatsuta Makoto

NUS Logic Seminar

1/12/2024 1:45:52

Invitation to the Logic Seminar at the National University of Singapore
Date: Wednesday, 17 January 2024, 17:00 hrs
Place: NUS, Department of Mathematics, S17#04-05
Speaker: Tatsuta Makoto
Title: Brotherston's Conjecture: Equivalence of Inductive Definitions
and Cyclic Proofs
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html
An inductive definition is a way to define a predicate by an
expression which may contain the predicate itself. The predicate
is interpreted by the least fixed point of the defining equation.
Inductive definitions are important in computer science, since
they can define useful recursive data structures such as lists and trees.
Inductive definitions are important also in mathematical logic,
since they increase the proof theoretic strength. Martin-Loef's
system of inductive definitions given in 1971 is one of the
most popular system of inductive definitions.
In 2006 Brotherston proposed an alternative formalization
of inductive definitions, called a cyclic proof system.
In general, for proof search, a cyclic proof system can find
an induction formula in a more efficient way than Martin-Loef's
system, since a cyclic proof system does not have to choose
fixed induction formulas in advance.
The equivalence of the provability of Martin-Loef's system for
inductive definitions and that of the cyclic proof system was
conjectured in 2006. The speaker and Berardi solved it in 2017.
This talk will explain this problem.

## 41st Nankai Logic Colloquium

Nankai Logic Colloquium

1/11/2024 1:25:50

Hello everyone,

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

Our speaker this week will be Felipe Garcia-Ramos from Jagiellonian University. This talk is going to take place this Friday, Jan 12, from 4pm to 5pm(UTC+8, Beijing time).

Title: Local entropy theory and descriptive complexity.

Abstract: We will discuss the descriptive complexity of families of dynamical systems that appear in the context of local entropy theory, such as completely positive entropy, uniform positive entropy, and completely positive mean dimension.

The talk will contain joint work with Udayan Darji and joint work with Yonatan Gutman.

_____________________________________________________________________________________________________

Title ：The 41st Nankai Logic Colloquium --Felipe Garcia-Ramos

Time ：16:00pm, Jan. 12, 2024(Beijing Time)

Zoom Number ： 708 354 1963

Passcode ： 477893

Link ：https://zoom.us/j/7083541963?pwd=cEcxRUgzNEtaWXJMeGszU2NCclVLZz09&omn=93150685735

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## KGRC Talks - January 8-12

Kurt Godel Research Center

1/6/2024 9:44:06

The KGRC welcomes as guest:
Aleksander Cieślak (host: Damian Sobota) visits January 8-12, 2024.
* * * * * * * * *
The KGRC/Institute of Mathematics invites you to the following talks:
(updates at https://kgrc.univie.ac.at/eventsnews/)
SET THEORY SEMINAR,
Kolingasse 14-16, 1090, 1st floor, SR 10,
TUESDAY, January 9, 3:00pm - 4:30pm, hybrid mode. (Please note the unusual date
and time!)
"Cofinalities of tree ideals"
A. Cieślak (Wrocław U of Technology, PL)
If $\mathcal{T}$ is a collection of trees on $\omega^\omega$, then we
define the tree ideal $t_0$ as a collection of these $X\subset
\omega^\omega$ such that each $T\in\mathcal{T}$ has a subtree
$S\in\mathcal{T}$ which shares no branches with $X$. We will be interested
in the cofinalities of tree ideals. Building on the work of Brendle,
Khomskii, and Wohofsky, we will analyse the condition called
"Incompatibility Shrinking Property", which implies that
$cof(t_0)>2^\omega$. We will investigate under which assumptions this
property is satisfied for two types of trees. These types are Laver and
Miller trees which split positively according to some fixed ideal on
$\omega$.
Joint work with Arturo Martinez Celis.
Zoom: If you have not received the Zoom data by the day before the talk,
please contact petra.czarnecki@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * * * * * * * *
SET THEORY SEMINAR,
Kolingasse 14-16, 1090, 1st floor, SR 10,
Thursday, January 11, 11:30am - 1:00pm, hybrid mode.
"Forcing techniques for Cichoń's Maximum: FS iterations with measures and
ultrafilters on the natural numbers"
D. A. Mejía (Shizuoka U, JP)
Mini-course (30.11.2023-25.01.2024, 6 lectures) - 4th lecture:
We complete the proof of the consistency of the constellation for the left
side of Cichoń's diagram by showing how to preserve a strong witness for
the unbounding number. However, this requires a modification of the
iteration, and a new theory of iterations with measures and ultrafilters.
Zoom: If you have not received the Zoom data by the day before the talk,
please contact petra.czarnecki@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * * * * * * * *
LOGIC COLlOQUIUM, Faculty of Mathematcs/KGRC,
Oskar-Morgenstern-Platz 1, 1090, 2nd floor, HS 11,
Thursday, January 11, 3:00pm - 3:50pm, hybrid mode.
"The Model Theoretic Covering Reflection Property"
A. Lietz (TU Wien)
The Covering Reflection Property holds at a cardinal $\kappa$ if for every
first order structure $\mathcal B$ in a countable language, there is some
$\mathcal A$ of size $<\kappa$ so that $\mathcal B$ can be covered with
the ranges of elementary embeddings $j:\mathcal A\rightarrow \mathcal B$.
That is, for every $b\in\mathcal B$, there is some $a\in\mathcal A$ and an
elementary embedding $j:\mathcal A\rightarrow\mathcal B$ with $j(a)=b$. We
discuss this property and isolate a new large cardinal notion strictly
between almost huge and huge cardinals and show that the least cardinal
exhibiting the Covering Reflection Property is exactly the least such
large cardinal. Moreover, there is a natural correspondence between such
large cardinals and strong forms of the Covering Reflection Property.
This is joint work with Joel D. Hamkins, Nai-Chung Hou and Farmer
Schlutzenberg.
Zoom: If you have not received the Zoom data by the day before the talk,
please contact petra.czarnecki@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
--
Mag. Petra Czarnecki de Czarnce-Chalupa
Institute of Mathematics (Kurt Goedel Research Center)
University of Vienna
Kolingasse 14-16, #7.48
1090 Vienna, Austria
Phone: +43/ (0)1 4277-50501

## set theory and topology seminar 9.01.2024 Piotr Borodulin-Nadzieja

Wrocław Set Theory Seminar

1/4/2024 11:19:58

I am happy to announce that at the seminar in Set Theory and Topology on Tuesday 9.01.2024 at 17:15 in room 601 (Mathematical Institute, University of Wrocław) the lecture:

"Fams on omega"

will be presented by

**Piotr Borodulin-Nadzieja**

Abstract.

I will review some recent results about finitely additive measures on omega. In particular, I will talk about some new examples of such measures, motivated by the problem if there is a P-measure in the Silver model. Joint work with Jonathan Cancino and Adam Morawski.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room.

## Wednesday seminar

Prague Set Theory Seminar

1/4/2024 10:22:41

Dear all,
The seminar meets on Wednesday January 10th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Matteo Casarosa -- Nonvanishing derived limits and
(generalized) cardinal characteristics
Combinatorial set theory has long proven useful in dealing with the
so-called derived limits. These functors in turn are related to several
problems in algebraic topology, such as the additivity of Strong
Homology. Set-theoretic methods have yielded both vanishing and
nonvanishing consistency results for these functors when computed on
certain inverse systems of abelian groups indexed either on the ordinals
or the (generalized) Baire space. In the second case, nonvanishing
results have so far assumed the existence of a scale (i.e. a linear
cofinal subset in the mod finite quasi-order). In this presentation, we
discuss some recent developments in the case where such a set does not
exist, including some work in progress with Jeffrey Bergfalk.
Best,
David

## 40th Nankai Logic Colloquium

Nankai Logic Colloquium

1/2/2024 9:47:34

Hello everyone,

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

Our speaker this week will be Steve Jackson from the University of North Texas. This talk is going to take place this Friday, Jan 05, from 4pm to 5pm(UTC+8, Beijing time).

Title: Forcing, hyperaperiodicity, and marker techniques in Borel equivalence relations.

Abstract: We will survey some of the useful techniques that have developed for the study of continuous and Borel actions of countable groups. These include hyperaperiodicity, forcing methods, and various marker techniques. We will present some previous results which use these techniques and also present some more recent results along with some currently open problems. For example, using some of the new methods we can show that there is no continuous k-line section or even k-treeing for the free part of the shift action of Z^2. We also present some results concerning finite asymptotic dimension for equivalence relations.

_____________________________________________________________________________________________________

Title ：The 40th Nankai Logic Colloquium --Steve Jackson

Time ：16:00pm, Jan. 5, 2024(Beijing Time)

Zoom Number ： 393 758 7647

Passcode ： 055758

Link ：https://us06web.zoom.us/j/3937587647?pwd=RdX4CjblPBY3xABriIFSFI8iUqHSfI.1&omn=81620949347

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## Wednesday seminar

Prague Set Theory Seminar

1/2/2024 8:50:19

Dear all,
The seminar meets tomorrow, Wednesday January 3rd at 11:00 in the
Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front
building.
The program is not yet decided, walk-in speakers will be welcomed.
Best,
David

## Stationary Sets and Algebra, VCU, May 20, 2024

Conference

12/30/2023 10:54:43

We will host a workshop at VCU from May 20-22, 2024, on recent applications of set theory to problems in algebra. The website is here:
https://stationarysetsandalgebra2024.wordpress.com/
The program and format will depend on the interests and backgrounds of the participants, but the goal is for the workshop to be accessible to graduate students and postdocs who have at least some exposure to set theory, model theory, or logic.
The workshop is funded by NSF grant DMS-2154141.
Please let Sean Cox (scox9@vcu.edu) know if you are interested in attending. There is some travel funding for student and postdoc participants.
Organizers: Sean Cox and Brent Cody

## 39th Nankai Logic Colloquium

Nankai Logic Colloquium

12/27/2023 10:54:43

Hello everyone,

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

Our speaker this week will be Yinhe Peng from the Academy of Mathematics and Systems Science, CAS. This talk is going to take place this Friday, Dec 29, from 4pm to 5pm(UTC+8, Beijing time).

Title: The topological basis problem under different assumptions

Abstract: For a class $\mathcal{K}$ of uncountable regular topological spaces, a subclass $\mathcal{B}$ is a basis if every space in $\mathcal{K}$ contains a subspace in $\mathcal{B}$. An important and interesting problem in set-theoretic topology is the topological basis problem: which class of topological spaces has a finite (or even 3-element) basis?

In this talk, I will first briefly recall several known results of the topological basis problem on different classes of spaces. Then, I will introduce recent progress on the topological basis problem under various assumptions. For example, together with Liuzhen Wu, we prove that

(1) under ZF+AD, the class of regular spaces of size $\geq$ continuum has a 3 element basis;

(2) under ZF+AD+V=L($\mathbb{R}$), the class of uncountable regular spaces has a 4 element basis.

I will also introduce definable version of the topological basis problem under ZFC.

_____________________________________________________________________________________________________

Title ：The 39th Nankai Logic Colloquium --Yinhe Peng

Time ：16:00pm, Dec. 29, 2023(Beijing Time)

Zoom Number ： 393 758 7647

Passcode ： 055758

Link ：https://us06web.zoom.us/j/3937587647?pwd=RdX4CjblPBY3xABriIFSFI8iUqHSfI.1&omn=83015084221

_____________________________________________________________________

The records of past talks can be accessed at https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## BLAST, North Texas, April 6-9, 2024

Conference

12/20/2023 14:03:10

We would like to bring your attention to the upcoming BLAST 2024 conference, which will take place at the University of North Texas in Denton, TX on April 6-9, 2024.
There will be an excursion on April 8 to Dallas, TX to witness the total eclipse.
BLAST is a conference series focusing on Boolean Algebras, Lattices, Universal Algebra and Model Theory, Set Theory, and Topology.
Invited Speakers
Monroe Eskew (University of Vienna)
Vera Fischer (University of Vienna)
Ralph Freese (University of Hawaii)
Gabriel Goldberg (UC Berkeley)
Jan Grebík (UCLA)
Diana Montoya (TU Wien)
Justin Moore (Cornell University)
Dmitri Pavlov (Texas Tech)
Sandra Müller (TU Wien)
David Simmons (University of York)
Dima Sinapova (Rutgers University)
Slawomir Solecki (Cornell University)
Šárka Stejskalová (Charles University)
Tutorials
Andrew Marks (UC Berkeley)
Agnes Szendrei (University of Colorado)
There is financial support available for students and young researchers which is provided by the NSF to attend the conference and give a contributed talk. Please see the website for details.
https://www.math.unt.edu/~ntrang/blast2024/
If you have any questions, feel free to contact us at BLAST2024@unt.edu.
Best regards,
Lior Fishman, Steve Jackson, John Krueger, Nam Trang

Tagged: Monroe Eskew, Vera Fischer, Ralph Freese, Gabriel Goldberg, Jan Grebik, Diana Montoya, Justin Moore, Dmitri Pavlov, Sandra Müller, David Simmons, Dima Sinapova, Slawomir Solecki, Šárka Stejskalová

## Wednesday seminar

Prague Set Theory Seminar

12/17/2023 14:03:10

Dear all,
The seminar meets on Wednesday December 20th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
The program is not yet decided, walk-in speakers are welcome. The backup
option is Chris Lambie-Hanson giving a spontaneous talk.
Let me also remind you that the Christmas meeting of the Institute will
take place on Wednesday December 20th at 16:00 in the blue lecture room.
All friends of the Institute are invited.
Best,
David

## Set Theory Seminar 19.12.2023 Aleksander Cieślak

Wrocław Set Theory Seminar

12/15/2023 14:13:22

I am happy to announce that at the seminar in Set Theory and Topology on Tuesday 19.12.2023 at 17:15 in room 601 (Mathematical Institute, University of Wrocław) the lecture:

"Antichain numbers and other cardinal invariants of ideals "

will be presented by

**Aleksander Cieślak**

Abstract.

Suppose that J is an ideal on \omega. The J-antichain number is the smallest cardinality of a maximal antichain in the algebra P(\omega) modulo J. We will estimate the J-antichain numbers for various Borel ideals. To do so, we will focus on two features of ideals which are crucial for our construction. First one is a cardinal invariant of an ideal J which lies (strictly) in between add*J and cov*J. The second one is a property which allows diagonalisation of antichains and which is similar (but not equal) to being a P^+ ideal.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room.

## 38th Nankai Logic Colloquium

Nankai Logic Colloquium

12/14/2023 5:06:34

Hello everyone,

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

Our speaker this week will be Forte Shinko from the University of California, Berkeley. This talk is going to take place this Friday, Dec 15, from 9am to 10am(UTC+8, Beijing time).

We are pausing our colloquium for once next week, due to the Annual Meeting of the Chinese Mathematical Society 2023. The Colloquium will be resumed Dec. 29.

Title: Hyperfiniteness of generic actions on Cantor spaceAbstract: A countable discrete group is exact if it has a free action on Cantor space which is measure-hyperfinite, that is, for every Borel probability measure on Cantor space, there is a conull set on which the orbit equivalence relation is hyperfinite. For an exact group, it is known that the generic action on Cantor space is measure-hyperfinite, and it is open as to whether the generic action is hyperfinite; an exact group for which the generic action is not hyperfinite would resolve a long-standing open conjecture about whether measure-hyperfiniteness and hyperfiniteness are equivalent. We show that for any countable discrete group with finite asymptotic dimension, its generic action on Cantor space is hyperfinite. This is joint work with Sumun Iyer._____________________________________________________________________________________________________

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 38th Nankai Logic Colloquium --Forte Shinko

Time ：9:00am, Dec. 15, 2023(Beijing Time)

Zoom Number ： 803 835 0307

Passcode ： 266169

Link ：https://us06web.zoom.us/j/8038350307?pwd=SisXBBK3gNWNaGdSTQtTbrdCoZn01g.1&omn=84935506346

_____________________________________________________________________

The records of past talks can be accessed from https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## (KGRC) one talk TOMORROW, December 12, two talks on Thursday, December 14

Kurt Godel Research Center

12/11/2023 13:09:40

The KGRC welcomes as guests:
David Asperó (host: Monroe Eskew) visits the KGRC from December 11 to
December 15.
Piotr Kowalski (host: Matthias Aschenbrenner) visits the KGRC from
December 13 to December 15.
* * *
Set Theory Seminar
Kurt Gödel Research Center
Tuesday, December 12
"Forcing with end-extendible virtual models"
David Asperó (University of East Anglia, Norwich, UK)
We address the problem of obtaining the saturation of the nonstationary
ideal on $\omega_2$ restricted to cofinality $\omega_1$ by forcing with
side conditions consisting of virtual models with generators. This is
joint work with Boban Velickovic.
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 have not received the Zoom data, please contact
richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * *
Set Theory Seminar
Kurt Gödel Research Center
Thursday, December 14
"Forcing techniques for Cichoń's Maximum: Preservation theory for cardinal
characteristics III"
Diego Alejandro Mejía (Shizuoka University, JP)
Mini-course (30.11.2023-25.01.2024, 6 lectures) - 3rd lecture:
We now deal with the more difficult task of forcing the converse
inequalities on the left side of Cichon's diagram. We first show how Cohen
reals add suitable Tukey connections (or what we also call "strong
witnesses"). Next, we need to preserve such Tukey connections along FS
iterations. For this purpose, we use a modern device of a preservation
technique from Judah and Shelah (1990), and Brendle (1991), illustrating
how combinatorial properties of forcing notions influence the preservation
of such Tukey connections. However, serious problems related to the
bounding number remain, which motivates more recent research that will be
presented in the fourth lecture.
Time and Place
Talk at 11:30am 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 have not received the Zoom data, please contact
richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, December 14
"Galois actions of finitely generated groups rarely have model companions"
Piotr Kowalski (Uniwersytet Wrocławski, PL)
This is joint work with Özlem Beyarslan. In our previous work (published
as "Model theory of fields with virtually free group actions", Proc.
London Math. Soc., (2) 118 (2019), 221-256), we used an erroneous argument
in the proof of Theorem 3.6 saying that if $G$ is a finitely generated
virtually free group, then the theory of $G$-actions on fields has a model
companion. In our recent paper (to appear in Bull. London Math. Soc.), we
show a "strong negation" of the statement from Theorem 3.6 above, that is,
we show that if $G$ is an infinite finitely generated virtually free
group, then the theory of $G$-actions on fields has a model companion if
and only if $G$ is free. In this talk, I will present some results and
conjectures regarding the companionability of the theory of group actions
on fields and (time permitting) discuss some related proofs.
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 have not received the Zoom data, please contact
richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.

## This Week in Logic at CUNY

This Week in Logic at CUNY

12/10/2023 22:22:00

Hi everyone,

This will be the final edition of This Week in Logic at CUNY for the Fall 2023 semester. Regular mailings will resume at the end of January.

Wishing you a happy and safe holiday season,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Dec 11, 2023 - - - -

Rutgers Logic Seminar

Monday, Dec 11, 3:30pm, Rutgers University, Hill 705

Eyal Kaplan, Berkeley

Preserving the Ultrapower Axiom in forcing extensions

Logic and Metaphysics Workshop

Date: Monday, Dec 11, 4.15-6.15pm (NY time)

Room: Graduate Center Room 4419

Rohit Parikh (CUNY)

Title: The logic of social choice

Abstract: Logic entered social choice theory through Kenneth Arrow who was a student of the logician Alfred Tarski at City College of New York. Arrow’s impossibility result, which was axiomatic in nature, showed that there is no rational procedure to define the popular choice when there are three or more candidates. Arrow’s result led to a rich field. However, subsequent work has concentrated on what happens when voters face a slate of three or more candidates. There is not enough work on a theory of candidate slates themselves. Thus an election with just Donald Trump and Joe Biden is seen as unproblematic since there are only two candidates. The actual quality of the candidates does not matter. We will propose a method which depends on the actual quality of a candidate. Then it becomes a dominant game theoretic strategy for each party to nominate as good a candidate as possible. The goodness of a candidate is defined in terms of a dot product of two vectors: the candidate’s position and the position of a typical voter.

- - - - Tuesday, Dec 12, 2023 - - - -Models of Peano Arithmetic (MOPA)

Tuesday, Dec 12, 1:00pm

Virtual (email Victoria Gitman

vgitman@gmail.com for meeting id)

Karel Hrbáček, CUNY

**Multi-level nonstandard analysis, the axiom of choice, and recent work of R. Jin**

Model-theoretic frameworks for nonstandard methods require the existence of nonprincipal ultrafilters over N, a strong form of the Axiom of Choice (AC). While AC is instrumental in many abstract areas of mathematics, its use in infinitesimal calculus or number theory should not be necessary.

In the paper KH and M. G. Katz, Infinitesimal analysis without the Axiom of Choice, Ann. Pure Applied Logic 172, 6 (2021), https://arxiv.org/abs/2009.04980, we have formulated SPOT, a theory in the language that has, in addition to membership, a unary predicate 'is standard.' The theory extends ZF by three simple axioms, Transfer, Nontriviality and Standard Part, that reflect the insights of Leibniz. It is a subtheory of the nonstandard set theories IST and HST, but unlike them, it is a conservative extension of ZF. Arguments carried out in SPOT thus do not depend on any form of AC. Infinitesimal calculus can be developed in SPOT. A stronger theory SCOT is a conservative extension of ZF + Dependent Choice. It is suitable for handling such features as an infinitesimal approach to the Lebesgue measure.

Renling Jin recently gave a groundbreaking nonstandard proof of Szemeredi's theorem in a model-theoretic framework that has three levels of infinity. I will formulate and motivate SPOTS, a multi-level version of SPOT, carry out Jin's proof of Ramsey's theorem in SPOTS, and discuss how his proof of Szemeredi's theorem can be developed in it.

While it is still open whether SPOTS is conservative over ZF, SCOTS (the multi-level version of SCOT) is a conservative extension of ZF + Dependent Choice.

- - - - Wednesday, Dec 13, 2023 - - - -

- - - - Thursday, Dec 14, 2023 - - - -

* EXAMS WEEK CUNY GRADUATE CENTER *

- - - - Friday, Dec 15, 2023 - - - -

Next Week in Logic at CUNY:

- - - - Monday, Dec 18, 2023 - - - -

- - - - Tuesday, Dec 19, 2023 - - - -

- - - - Wednesday, Dec 20, 2023 - - - -

- - - - Thursday, Dec 21, 2023 - - - -

- - - - Friday, Dec 22, 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

12/10/2023 15:04:47

Dear all,
The seminar meets on Wednesday December 13th at 11:00 in the Institute
of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Šárka Stejskalová -- Forcing over a free Suslin tree
In the talk I will discuss a joint work with John Krueger which leads to
a positive solution of a question from 1997 of Jin and Shelah for
omega_1-trees: Is there a model where there are no Kurepa trees, but
there is a ccc forcing with size at most omega_1 which adds a Kurepa
tree? We will start by discussing related concepts of an almost Kurepa
Suslin tree and a Suslin tree with more than omega_1-many automorphisms.
Then we will sketch a proof for the positive solution of Jin and
Shelah's question using a forcing over a free Suslin tree. We will
demonstrate the method in more detail by solving another open question
by Moore: Is there a model where there are no Kurepa trees, but there is
an Aronszajn tree which is not saturated? (An omega_1-tree is said to be
saturated if every family of subtrees with pairwise countable
intersections has size at most omega_1.)
Best,
David

## 37th Nankai Logic Colloquium

Nankai Logic Colloquium

12/7/2023 1:00:38

Hello everyone,

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

Our speaker this week will be Wei He from Nanjing Normal University. This talk is going to take place this Friday, Dec 08, from 9am to 10am(UTC+8, Beijing time).

Title: Ordered Structure of Topological Groups

Abstract: In this talk, we discuss the ordered structure of the lattices of group topologies on an abstract group. We are in particular concerned with the gaps and distributive conditions of the lattice of group topologies.

We will see that the order structure of the group topologies is closely connected with the algebraic structure and the topological structure of a topological group.

_____________________________________________________________________________________________________

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

Title ：The 37th Nankai Logic Colloquium --Wei He

Time ：9:00pm, Dec. 8, 2023(Beijing Time)

Zoom Number ： 803 835 0307

Passcode ： 266169

_____________________________________________________________________

The records of past talks can be accessed from https://space.bilibili.com/253421893.

Best Wishes,

Ming Xiao

## (KGRC) CORRECTED: the future of KGRC announcements, plus three talks

Kurt Godel Research Center

12/5/2023 12:50:03

The following corrects announcements sent a few minutes ago that stated
the wrong time for Julia Wolf. The time is 3:00pm. Apologies for any
confusion caused!
* * *
Dear all,
The KGRC needs to reorganize event announcements. This includes the way
the list of recipients is maintained. If you would like to receive these
announcements in the future, please register your mail address at
https://kgrc.univie.ac.at/newsletter/
For next week announcements will be sent to the current list and the new
list in parallel. If you do not want to receive event announcements beyond
that, no action is required on your part.
Thank you!
* * *
The KGRC welcomes as guests:
Andre Nies (host: Matthias Aschenbrenner) visits the KGRC until December
19 and gives a talk, see below.
David Asperó (host: Monroe Eskew) visits the KGRC from December 11 to
December 15.
Piotr Kowalski (host: Matthias Aschenbrenner) visits the KGRC from
December 13 to December 15.
* * *
Model Theory Seminar
Kurt Gödel Research Center
Wednesday, December 6
"Tame regularity in hypergraphs"
Julia Wolf (Cambridge University, UK)
Szemerédi's celebrated regularity lemma states, roughly speaking, that the
vertex set of any large graph can be partitioned into a bounded number of
sets in such a way that all but a small proportion of pairs of sets from
this partition induce a 'regular' graph. The example of the half-graph
shows that the existence of irregular pairs cannot be ruled out in
general. Recognising the half-graph as an instance of the so-called 'order
property' from model theory, Malliaris and Shelah proved in 2014 that if
one assumes that the large graph contains no half-graphs of a fixed size
(as induced bipartite subgraphs), then it is possible to obtain a
regularity partition with no irregular pairs. In addition, the number of
parts of the partition is polynomial in the regularity parameter, and the
density of each regular pair is either close to zero or close to 1. This
beautiful result exemplifies a long-standing theme in model theory, namely
that stable structures (which are characterised by an absence of large
instances of the order property), are extremely well-behaved. In this talk
I will present recent joint work with Caroline Terry (OSU), in which we
define a higher-arity generalisation of the order property and prove that
its absence characterises those large 3-uniform hypergraphs whose
regularity decompositions allow for particularly good control of the
irregular triads.
Time and Place
Talk at 3:00pm on-site
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.
* * *
Set Theory Seminar
Kurt Gödel Research Center
Thursday, December 7
"Forcing techniques for Cichoń's Maximum: FS iterations"
Diego Alejandro Mejía (Shizuoka University, JP)
Mini-course (30.11.2023-25.01.2024, 6 lectures) - 2nd lecture:
We review FS (finite support iterations) of forcing notions, basic facts,
and how they are typically used to modify cardinal characteristics of the
continuum. These tools allow to force “one inequality” of the intended
models, but a more complex theory is required to force the “converse
inequalities”. The latter will be the main topic of the next session.
Time and Place
Talk at 11:30am 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 have not received the Zoom data, please contact
richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, December 7
"The unit conjecture and the unique product property"
Andre Nies (University of Auckland, NZ)
A torsion free group $G$ satisfies the trivial units property for a field
$K$ if the group algebra $K[G]$ only has the trivial units (the ones of
the form $kg$, where $k$ is a nonzero field element and $g$ is in $G$).
$G$ satisfies the unique product property if for each pair of finite
nonempty subsets $A$, $B$ some product in $AB$ can be written uniquely.
The unique product property implies the trivial units property for each
field.
We give an overview over these and related properties, and how to
formulate them in first-order logic. We discuss Gardam's 2021 result that
$F_2[G]$ (where $F_2$ is the two-element field) fails the unit conjecture
for the Hantzsche-Wendt group $G$, and the computational methods used to
obtain a counterexample.
We discuss work in progress with Heiko Dietrich and Melissa Lee (Monash)
that would yield a group $G$ for which the trivial units property for
$F_2$ holds but the unique product property fails.
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 have not received the Zoom data, please contact
richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.

## UPDATE - This Week in Logic at CUNY

This Week in Logic at CUNY

12/5/2023 9:56:58

Hi everyone,

Please note the addition of a talk on Dec 11 by Rohit Parikh in the Logic and Metaphysics Workshop.

Best,

Jonas

This Week in Logic at CUNY:

- - - - Monday, Dec 4, 2023 - - - -

Rutgers Logic Seminar

Monday, Dec 4, 3:30pm, Rutgers University, Hill 705

Joel David Hamkins, Notre Dame

The computable model theory of forcing

Logic and Metaphysics Workshop

Date: Monday, Dec 4, 4.15-6.15pm (NY time)

Room: Graduate Center Room 4419

James Walsh (NYU)

Title: Use and mention in formal languages

Abstract: Quine’s distinction between use and mention is one of the cornerstones of analytic philosophy. The distinction is typically motivated with examples from natural language, but Quine also applied the distinction to the formal languages studied in mathematical logic. I will argue that such expressions are not used in Quine’s sense, so the distinction cannot appropriately be applied to them. Accordingly, the standard practice of placing quotation marks around expressions of formal languages is incorrect. This technical point serves as a springboard for discussing the role that formal languages play in mathematical logic.

- - - - Tuesday, Dec 5, 2023 - - - -Models of Peano Arithmetic (MOPA)

Tuesday, Dec 5, 1:00pm

Virtual (email Victoria Gitman

vgitman@gmail.com for meeting id)

**Simplest model properties for Peano Arithmetic: On a question of Montalban and Rossegger**

As famously shown by Scott, every countable structure can be characterized, up to isomorphism, by a sentence of infinitary language Lω1,ω which allows for conjunctions and disjunctions over arbitrary countable families of formulae (over finitely many variables). Formulae of this language can be naturally assigned ranks based on the number of alternations of existential connectives (disjunctions and existential quantifiers) with universal ones (conjunctions and universal quantifiers). This gives rise to a natural complexity measure for countable models: the Scott rank of a model M is the least α such that M can be uniquely characterized by a sentence of rank α+1 (and starting from the universal quantifier). The developments of computable model theory witness that the Scott rank is a very robust notion integrating other well established tools from descriptive set theory, model theory and computability.

In 'The Structural Complexity of Models of Arithmetic' Antonio Montalban and Dino Rossegger pioneered the Scott analysis of models of Peano Arithmetic. They characterized the Scott spectrum of completions PA , i.e. the set of ordinals which are Scott ranks of countable models of a given completion T of PA. A particularly intriguing outcome of their analysis is that PA has exactly one model of the least rank, the standard model, and the Scott rank of every other model is infinite. Additionally they studied the connections between Scott ranks and model-theoretical properties of models, such as recursive saturation and atomicity, raising an open question: is there a non-atomic homogeneous model of PA of Scott rank ω?

In the talk we answer the above question to the negative, showing that the nonstandard models of PA or rank ω are exactly the nonstandard prime models. This witness another peculiar property of PA: not only it has the simplest model, but also its every completion has a unique model of the least Scott rank. This is joint work with Patryk Szlufik.

- - - - Wednesday, Dec 6, 2023 - - - -

- - - - Thursday, Dec 7, 2023 - - - -

- - - - Friday, Dec 8, 2023 - - - -

Model Theory Seminar

Friday, Dec 8, 12:30-2:00pm NY time, Room 5383

David Marker, University of Illinois at Chicago

Rigid real closed fields?

Every archimedean real closed field is rigid, i.e., has no nontrivial automorphisms. What happens in the non-archimedean case? Shelah showed it is consistent that there are uncountable rigid non-archimedean real closed fields. Enayat asked what happens in the countable case. I believe the question is even interesting in the finite transcendence degree case. In this talk I will describe Shelah's proof and discuss some interesting phenomenon that arises even in transcendence degree 2.

Logic Workshop

CUNY Graduate Center

Friday Dec 8, 2:00pm-3:30pm, Room 5417

**Michael Benedikt**, Oxford University

**Nested Data, Views, and Gaifman Coordinization**

I will begin with an overview of how implicit definition, and variations of Beth's definability theorem, arise in relational databases, particularly in the context of view rewriting.

We then turn from relational databases to nested relational databases, a model of hierarchical data - 'objects' - where tables can contain tuples whose components are again tables. There is a standard transformation language for this data model, the Nested Relational Calculus (NRC). We show that a variant of Gaifman's coordinatization theorem plays a role in lieu of Beth's theorem, allowing one to generate NRC transformations from several kinds of implicit specifications. We discuss how to generate transformations effectively from specifications, which requires the development of proof-theoretic methods for implicit definability over nested sets.

This is joint work with Ceclia Pradic and Christoph Wernhard.

Next Week in Logic at CUNY:

- - - - Monday, Dec 11, 2023 - - - -

Rutgers Logic Seminar

Monday, Dec 11, 3:30pm, Rutgers University, Hill 705

Eyal Kaplan, Berkeley

Preserving the Ultrapower Axiom in forcing extensions

Logic and Metaphysics Workshop

Date: Monday, Dec 11, 4.15-6.15pm (NY time)

Room: Graduate Center Room 4419

Rohit Parikh (CUNY)

Title: The logic of social choice

Abstract: Logic entered social choice theory through Kenneth Arrow who was a student of the logician Alfred Tarski at City College of New York. Arrow’s impossibility result, which was axiomatic in nature, showed that there is no rational procedure to define the popular choice when there are three or more candidates. Arrow’s result led to a rich field. However, subsequent work has concentrated on what happens when voters face a slate of three or more candidates. There is not enough work on a theory of candidate slates themselves. Thus an election with just Donald Trump and Joe Biden is seen as unproblematic since there are only two candidates. The actual quality of the candidates does not matter. We will propose a method which depends on the actual quality of a candidate. Then it becomes a dominant game theoretic strategy for each party to nominate as good a candidate as possible. The goodness of a candidate is defined in terms of a dot product of two vectors: the candidate’s position and the position of a typical voter.

- - - - Tuesday, Dec 12, 2023 - - - -Models of Peano Arithmetic (MOPA)

Tuesday, Dec 12, 1:00pm

Virtual (email Victoria Gitman

vgitman@gmail.com for meeting id)

Karel Hrbáček, CUNY

**Multi-level nonstandard analysis, the axiom of choice, and recent work of R. Jin**

Model-theoretic frameworks for nonstandard methods require the existence of nonprincipal ultrafilters over N, a strong form of the Axiom of Choice (AC). While AC is instrumental in many abstract areas of mathematics, its use in infinitesimal calculus or number theory should not be necessary.

In the paper KH and M. G. Katz, Infinitesimal analysis without the Axiom of Choice, Ann. Pure Applied Logic 172, 6 (2021), https://arxiv.org/abs/2009.04980, we have formulated SPOT, a theory in the language that has, in addition to membership, a unary predicate 'is standard.' The theory extends ZF by three simple axioms, Transfer, Nontriviality and Standard Part, that reflect the insights of Leibniz. It is a subtheory of the nonstandard set theories IST and HST, but unlike them, it is a conservative extension of ZF. Arguments carried out in SPOT thus do not depend on any form of AC. Infinitesimal calculus can be developed in SPOT. A stronger theory SCOT is a conservative extension of ZF + Dependent Choice. It is suitable for handling such features as an infinitesimal approach to the Lebesgue measure.

Renling Jin recently gave a groundbreaking nonstandard proof of Szemeredi's theorem in a model-theoretic framework that has three levels of infinity. I will formulate and motivate SPOTS, a multi-level version of SPOT, carry out Jin's proof of Ramsey's theorem in SPOTS, and discuss how his proof of Szemeredi's theorem can be developed in it.

While it is still open whether SPOTS is conservative over ZF, SCOTS (the multi-level version of SCOT) is a conservative extension of ZF + Dependent Choice.

- - - - Wednesday, Dec 13, 2023 - - - -

- - - - Thursday, Dec 14, 2023 - - - -

* EXAMS WEEK CUNY GRADUATE CENTER *

- - - - Friday, Dec 15, 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Wednesday seminar

Prague Set Theory Seminar

12/4/2023 7:03:15

Dear all,
The seminar meets on Wednesday December 6th at 11:00 in the Institute of
Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building.
Program: Wadge classes on omega_1 (2nd attempt)
This will be the second attempt at the seminar to introduce a game to
compare complexity of constructions of objects of size omega_1. The
original motivation was to compare constructions of Aronszajn trees,
coherent sequences of functions, gaps in P(omega), and similar objects.
I will prove some basic results on the resulting complexity classes.
Joint work (in progress) with J. Bergfalk, O. Guzman, M. Hrusak.
Best,
David

## Logic Seminar 5 Dec 2023 15:30 hrs at NUS by Lu Qi

NUS Logic Seminar

12/4/2023 5:13:16

Invitation to the Logic Seminar at the National University of Singapore
Date: Tuesday, 5 December 2023, 15:30 hrs
Place: NUS, Department of Mathematics, S17#04-04.
Speaker: Lu Qi.
Title: Convexity of multiplicities of filtrations on local rings
Abstract: In this talk, I will discuss some convexity properties of
multiplicities of filtrations on a local ring.
In particular, the multiplicity function is convex
along geodesics. As a major application, this gives
a new proof of a theorem due to Xu and Zhuang on
the uniqueness of normalized volume minimizers.
In order to characterize strict convexity,
we introduce the notion of saturation of
a filtration, which turns out to be useful
in other settings. For example, it allows us
to generalizes a theorem by Rees on characterization
of when two filtrations have equal multiplicities.
It also allows us to introduce a metric on the space
of filtrations.
Joint Work: This talk is based on joint work with Harold Blum
and Yuchen Liu and some ongoing work.
URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## This Week in Logic at CUNY

This Week in Logic at CUNY

12/3/2023 22:34:00

This Week in Logic at CUNY:

- - - - Monday, Dec 4, 2023 - - - -

Rutgers Logic Seminar

Monday, Dec 4, 3:30pm, Rutgers University, Hill 705

Joel David Hamkins, Notre Dame

The computable model theory of forcing

Logic and Metaphysics Workshop

Date: Monday, Dec 4, 4.15-6.15pm (NY time)

Room: Graduate Center Room 4419

James Walsh (NYU)

Title: Use and mention in formal languages

Abstract: Quine’s distinction between use and mention is one of the cornerstones of analytic philosophy. The distinction is typically motivated with examples from natural language, but Quine also applied the distinction to the formal languages studied in mathematical logic. I will argue that such expressions are not used in Quine’s sense, so the distinction cannot appropriately be applied to them. Accordingly, the standard practice of placing quotation marks around expressions of formal languages is incorrect. This technical point serves as a springboard for discussing the role that formal languages play in mathematical logic.

- - - - Tuesday, Dec 5, 2023 - - - -Models of Peano Arithmetic (MOPA)

Tuesday, Dec 5, 1:00pm

Virtual (email Victoria Gitman

vgitman@gmail.com for meeting id)

**Simplest model properties for Peano Arithmetic: On a question of Montalban and Rossegger**

As famously shown by Scott, every countable structure can be characterized, up to isomorphism, by a sentence of infinitary language Lω1,ω which allows for conjunctions and disjunctions over arbitrary countable families of formulae (over finitely many variables). Formulae of this language can be naturally assigned ranks based on the number of alternations of existential connectives (disjunctions and existential quantifiers) with universal ones (conjunctions and universal quantifiers). This gives rise to a natural complexity measure for countable models: the Scott rank of a model M is the least α such that M can be uniquely characterized by a sentence of rank α+1 (and starting from the universal quantifier). The developments of computable model theory witness that the Scott rank is a very robust notion integrating other well established tools from descriptive set theory, model theory and computability.

In 'The Structural Complexity of Models of Arithmetic' Antonio Montalban and Dino Rossegger pioneered the Scott analysis of models of Peano Arithmetic. They characterized the Scott spectrum of completions PA , i.e. the set of ordinals which are Scott ranks of countable models of a given completion T of PA. A particularly intriguing outcome of their analysis is that PA has exactly one model of the least rank, the standard model, and the Scott rank of every other model is infinite. Additionally they studied the connections between Scott ranks and model-theoretical properties of models, such as recursive saturation and atomicity, raising an open question: is there a non-atomic homogeneous model of PA of Scott rank ω?

In the talk we answer the above question to the negative, showing that the nonstandard models of PA or rank ω are exactly the nonstandard prime models. This witness another peculiar property of PA: not only it has the simplest model, but also its every completion has a unique model of the least Scott rank. This is joint work with Patryk Szlufik.

- - - - Wednesday, Dec 6, 2023 - - - -

- - - - Thursday, Dec 7, 2023 - - - -

- - - - Friday, Dec 8, 2023 - - - -

Model Theory Seminar

Friday, Dec 8, 12:30-2:00pm NY time, Room 5383

David Marker, University of Illinois at Chicago

Rigid real closed fields?

Every archimedean real closed field is rigid, i.e., has no nontrivial automorphisms. What happens in the non-archimedean case? Shelah showed it is consistent that there are uncountable rigid non-archimedean real closed fields. Enayat asked what happens in the countable case. I believe the question is even interesting in the finite transcendence degree case. In this talk I will describe Shelah's proof and discuss some interesting phenomenon that arises even in transcendence degree 2.

Logic Workshop

CUNY Graduate Center

Friday Dec 8, 2:00pm-3:30pm, Room 5417

**Michael Benedikt**, Oxford University

**Nested Data, Views, and Gaifman Coordinization**

I will begin with an overview of how implicit definition, and variations of Beth's definability theorem, arise in relational databases, particularly in the context of view rewriting.

We then turn from relational databases to nested relational databases, a model of hierarchical data - 'objects' - where tables can contain tuples whose components are again tables. There is a standard transformation language for this data model, the Nested Relational Calculus (NRC). We show that a variant of Gaifman's coordinatization theorem plays a role in lieu of Beth's theorem, allowing one to generate NRC transformations from several kinds of implicit specifications. We discuss how to generate transformations effectively from specifications, which requires the development of proof-theoretic methods for implicit definability over nested sets.

This is joint work with Ceclia Pradic and Christoph Wernhard.

Next Week in Logic at CUNY:

- - - - Monday, Dec 11, 2023 - - - -

Rutgers Logic Seminar

Monday, Dec 11, 3:30pm, Rutgers University, Hill 705

Eyal Kaplan, Berkeley

Preserving the Ultrapower Axiom in forcing extensions

- - - - Tuesday, Dec 12, 2023 - - - -Models of Peano Arithmetic (MOPA)Tuesday, Dec 12, 1:00pmVirtual (email Victoria Gitman vgitman@gmail.com for meeting id)Karel Hrbáček, CUNY

**Multi-level nonstandard analysis, the axiom of choice, and recent work of R. Jin**

Model-theoretic frameworks for nonstandard methods require the existence of nonprincipal ultrafilters over N, a strong form of the Axiom of Choice (AC). While AC is instrumental in many abstract areas of mathematics, its use in infinitesimal calculus or number theory should not be necessary.

In the paper KH and M. G. Katz, Infinitesimal analysis without the Axiom of Choice, Ann. Pure Applied Logic 172, 6 (2021), https://arxiv.org/abs/2009.04980, we have formulated SPOT, a theory in the language that has, in addition to membership, a unary predicate 'is standard.' The theory extends ZF by three simple axioms, Transfer, Nontriviality and Standard Part, that reflect the insights of Leibniz. It is a subtheory of the nonstandard set theories IST and HST, but unlike them, it is a conservative extension of ZF. Arguments carried out in SPOT thus do not depend on any form of AC. Infinitesimal calculus can be developed in SPOT. A stronger theory SCOT is a conservative extension of ZF + Dependent Choice. It is suitable for handling such features as an infinitesimal approach to the Lebesgue measure.

Renling Jin recently gave a groundbreaking nonstandard proof of Szemeredi's theorem in a model-theoretic framework that has three levels of infinity. I will formulate and motivate SPOTS, a multi-level version of SPOT, carry out Jin's proof of Ramsey's theorem in SPOTS, and discuss how his proof of Szemeredi's theorem can be developed in it.

While it is still open whether SPOTS is conservative over ZF, SCOTS (the multi-level version of SCOT) is a conservative extension of ZF + Dependent Choice.

- - - - Wednesday, Dec 13, 2023 - - - -

- - - - Thursday, Dec 14, 2023 - - - -

* EXAMS WEEK CUNY GRADUATE CENTER *

- - - - Friday, Dec 15, 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@citytech.cuny.edu.If you have a logic-related event that you would like included in future mailings, please email jreitz@citytech.cuny.edu.
## Set Theory and Topology Seminar 5.12.2023 Daria Perkowska

Wrocław Set Theory Seminar

12/1/2023 17:37:49

I am happy to announce that at the seminar in Set Theory and Topology on Tuesday 5.12.2023 at 17:15 in room 601 (Mathematical Institute, University of Wrocław) the lecture:

"Non-meager filters"

will be presented by

**Daria Perkowska**

Abstract.

In the talk I will consider filters on \omega in the measurability (and complexity) context. Also, one can distinguish some natural subclasses of non-meager filters. We say that a filter F is ccc if P(\omega) /F is ccc. Similarly, we say that a filter supports a measure if there is a probability measure \mu on \omega such that F = {A: \mu(A)=1}. I will show that every ultrafilter supports a measure, every measure supporting filter is ccc and every ccc filter is non-meager. So, one can think about these notions as forming some hierarchy of complexity of filters. This hierarchy is strict. Next I will show that for every ultrafilter from the forcing extension (by \mathbb{A}), there is a ground model filter F such that the ultrafilter extends F and there is an injective Boolean homomorphism \varphi: P(\omega) /F \to \mathbb{A}.

Feel free to spread this information among Your colleagues.

I'm looking forward to seeing You

Szymon Żeberski

(on behalf of the organizers, i.e. Piotr Borodulin-Nadzieja, Paweł Krupski, Aleksandra Kwiatkowska, Grzegorz Plebanek, Robert Rałowski and myself)

About 15 minutes before the seminar we invite you for coffee and a chat to social room.

## 36th Nankai Logic Colloquium

Nankai Logic Colloquium

11/29/2023 23:51:07

Hello everyone,

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

Our speaker this week will be Victor Hugo Yanez from Nanjing Normal University. This talk is going to take place this Friday, Dec 01, from 4pm to 5pm(UTC+8, Beijing time).

Title: An introduction to the Markov and Zariski topologies of a group

Abstract: Let $G$ be a group. A subset of $X$ is said to be \emph{elementary algebraic}, if it is the solution set on $G$ of a given equation of the form $g_1 x^{\varepsilon_1} g_2 x^{\varepsilon_2} \cdots g_n x^{\varepsilon_n} = 1$ for some $g_1, \dots, g_n \in G$ and integers $\varepsilon_1, \dots, \varepsilon_n \in \Z$. $X$ is \emph{algebraic} whenever it is an intersection of a finite union of elementary algebraic subsets of $G$. The algebraic subsets of a group $G$ form a basis of closed sets for a unique topology on $G$ known as the Zariski topology of $G$. Meanwhile, the family of all subsets of $G$ which are closed in every Hausdorff group topology of $G$ form a family of closed subsets for another unique topology on $G$ known as the \emph{Markov topology} of $G$. The Markov topology on a group is always finer than its Zariski topology.

An old 1945 problem of Markov asks whether the Markov and Zariski topologies of a group must always coincide. The goal of this talk is to give a humble introduction to the theory of the Markov and Zariski topologies; from the overall motivation and impact of the classic results of Markov, to more recent advances further enriching the solution of Markov's problem.

_____________________________________________________________________________________________________

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

_____________________________________________________________________

Best wishes,

Ming Xiao

## (KGRC) two seminar talks Thursday, November 30

Kurt Godel Research Center

11/28/2023 17:32:25

(The announcements sent a few minutes ago stated the wrong title for Professor Andretta's talk. Below are the
corrected announcements. Apologies for any confusion caused!)
* * *
The KGRC welcomes as guests:
David Schrittesser (host: Vera Fischer) visits the KGRC until January 8,
2024.
* * *
Set Theory Seminar
Kurt Gödel Research Center
Thursday, November 30
"Forcing techniques for Cichoń's Maximum"
Diego Alejandro Mejía (Shizuoka U, JP)
Mini-course (30.11.2023-25.01.2024, 6 lectures) - 1st lecture:
Cichoń's diagram describes the connections between combinatorial notions
related to measure, category, and compactness of sets of irrational
numbers. In the second part of the 2010's decade, Goldstern, Kellner and
Shelah constructed a forcing model of Cichoń's Maximum (meaning that all
non-dependent cardinal characteristics are pairwise different) by using
large cardinals. Some years later, we eliminated this large cardinal
assumption. In this mini-course, we explore the forcing techniques to
construct the Cichoń's Maximum model and much more. Concretely, we discuss
the following components: 1. Tukey connections and cardinal
characteristics of the continuum 2. Review of FS (finite support)
iterations and basic methods to modify cardinal characteristics. 3.
Preservation theory for cardinal characteristics. 4. FS iterations with
measures and ultrafilters on the natural numbers. 5. Boolean Ultrapowers.
6. Forcing Intersected with submodels.
Time and Place
Talk at 11:30am 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 have not received the Zoom data by the day before the talk,
please contact richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.
* * *
Logic Colloquium
Kurt Gödel Research Center
Thursday, November 30
"Sierpiński's theorem: geometric aspects and definability issues"
Alessandro Andretta (U of Turin, IT)
There are numerous statements in various areas of mathematics (algebra,
analysis, geometry, ...) that are equivalent to the continuum hypothesis
(CH). The earliest instance of this phenomenon is Sierpiński's theorem
from 1919: CH is equivalent to the existence of two sets covering the
plane such that every horizontal line has countable intersection with the
first set and every vertical line has countable intersection with the
second. Sierpiński's theorem is the blueprint for most other geometric
facts that are equivalent to CH. I will survey some of these theorems
proved in the last hundred years, and present some new results in this
area.
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 have not received the Zoom data by the day before the talk,
please contact richard.springer@univie.ac.at.
Please direct any other questions about this talk to
vera.fischer@univie.ac.at.

## Cross-Alps Logic Seminar (speaker: Zoltán Vidnyánszky)

Cross-Alps Logic Seminar

11/27/2023 9:55:02

On Friday 01.12.2023 at 16.00

**Zoltán Vidnyánszky** (Eötvös Loránd University)

will give a talk on

*Homomorphisms in the choiceless world*

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 2022 'Models, Sets and Classifications'.

All the best,

Vincenzo

## This Week in Logic at CUNY

This Week in Logic at CUNY

11/26/2023 22:32:00

This Week in Logic at CUNY:

- - - - Monday, Nov 27, 2023 - - - -

Logic and Metaphysics Workshop

Date: Monday, Nov 27, 4.15-6.15pm (NY time)

Room: Graduate Center Room 4419

Mircea Dumitru (Bucharest).

Title: Truth with and without satisfaction

Abstract: The talk addresses a quite natural situation in mathematics. When one needs to define a concept and it is not possible to do a direct recursion on the concept itself, what one does is the next best thing which is to perform recursion on a related concept of which the original given concept can be shown to be a special case. Tarski, in his celebrated paper on “The Concept of Truth in Formalized Languages”, cannot give a definition of truth performing direct recursion on the concept of truth itself. Consequently, he settles on a definition in terms of satisfaction. Following Kit Fine and Timothy McCarthy, “Truth without Satisfaction”, I raise the issue of whether such an indirect procedure of giving a definition of truth is necessary or maybe an alternative definition of truth can be given without going through the related concept of satisfaction. My talk will investigate both certain technical and philosophical aspects of the two sets of formal constraints to defining truth with and without satisfaction.

- - - - Tuesday, Nov 28, 2023 - - - -- - - - Wednesday, Nov 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

URL:

http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.htmlSpeaker: Charlotte Aten, University of Denver.

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

Title:** A categorical semantics for neural networks.**

Abstract: In recent work on discrete neural networks, I considered such networks whose activation functions are polymorphisms of finite, discrete relational structures. The general framework I provided was not entirely categorical in nature but did provide a stepping stone to a categorical treatment of neural nets which are definitionally incapable of overfitting. In this talk I will outline how to view neural nets as categories of functors from certain multicategories to a target multicategory. Moreover, I will show that the results of my PhD thesis allow one to systematically define polymorphic learning algorithms for such neural nets in a manner applicable to any reasonable (read: functorial) finite data structure.

- - - - Thursday, Nov 30, 2023 - - - -

- - - - Friday, Dec 1, 2023 - - - -

Model Theory Seminar

Friday, Dec 1, 12:30-2:00pm NY time, Room 5383

Rehana Patel Wesleyan University

Logic Workshop

CUNY Graduate Center

Friday Dec 1, 2:00pm-3:30pm, Room 6417

**James Walsh**, New York University

**Is the consistency operator canonical?**

It is a well-known empirical phenomenon that natural axiomatic theories are well-ordered by consistency strength. The restriction to natural theories is necessary; using ad-hoc techniques (such as self-reference and Rosser orderings) one can exhibit non-linearity and ill-foundedness in the consistency strength hierarchy. What explains the contrast between natural theories and axiomatic theories in general?

Our approach to this problem is inspired by work on an analogous problem in recursion theory. The natural Turing degrees (0,0′,…,Kleene’s~O,…,0#,…) are well-ordered by Turing reducibility, yet the Turing degrees in general are neither linearly ordered nor well-founded, as ad-hoc techniques (such as the priority method) bear out. Martin's Conjecture, which is still unresolved, is a proposed explanation for this phenomenon. In particular, Martin’s Conjecture specifies a way in which the Turing jump is canonical.

After discussing Martin’s Conjecture, we will formulate analogous proof-theoretic hypotheses according to which the consistency operator is canonical. We will then discuss results - both positive and negative - within this framework. Some of these results were obtained jointly with Antonio Montalbán.

Next Week in Logic at CUNY:

- - - - Monday, Dec 4, 2023 - - - -

Rutgers Logic Seminar

Monday, Dec 4, 3:30pm, Rutgers University, Hill 705

Joel David Hamkins, Notre Dame

The computable model theory of forcing

Logic and Metaphysics WorkshopDate: Monday, Dec 4, 4.15-6.15pm (NY time)Room: Graduate Center Room 4419James Walsh (NYU)

Title: Use and mention in formal languages

Abstract: Quine’s distinction between use and mention is one of the cornerstones of analytic philosophy. The distinction is typically motivated with examples from natural language, but Quine also applied the distinction to the formal languages studied in mathematical logic. I will argue that such expressions are not used in Quine’s sense, so the distinction cannot appropriately be