# Set Theory Talks

Global set theory seminar and conference announcements

## Wednesday seminar

Prague Set Theory Seminar
Dear all, The seminar meets on Wednesday November 3rd at 11:00 in the Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building. Program: Paul Szeptycki -- An example from a square-sequence, convergence and the G_delta-topology. Questions of Bella concerning cardinal invariants of the G_delta topology and questions of Arhangel'skii on strong convergence properties are answered with examples constructed from square(kappa) sequences. Best, David

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

The next session of the Barcelona Set Theory Semina will take place tomorrow:

SPEAKER:   Martina Iannella (Università degli Studi di Udine)
TITLE: Convex embeddability on linear/circular orders and connections to knot theory
DATE: 27 October 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online via Zoom:

Announcement attached below.

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609
joan.bagaria@icrea.cat
bagaria@ub.edu

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Oct 25, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 25, 4.15-6.15 (NY time)

Noah Friedman-Biglin (San José State University)
Title: Regrounding the Unworldly: Pluralism and Politics in Carnap’s Philosophy of Logic

Abstract: The locus classicus of logical pluralism – that is, the view that there is more than on logic, properly so called – since the earliest days of analytic philosophy, can be found in Rudolf Carnap’s ‘principle of tolerance’. Clarifying the principle of tolerance is the focus of this first section of this paper. I will argue that the principle should be understood as widely as possible, and thus we will see that Carnap’s tolerance is a very radical view. In section two, I discuss the motivations Carnap had for his pluralism, and argue that they are based in the Vienna Circle’s “Scientific World-Conception” — a platform of philosophical commitments which set the direction for the Circle’s philosophical investigations as well as a program of social change. What emerges from this discussion is the often-ignored relationship between his logical pluralism and his political views. In short, I will argue that the radical quality of his tolerance is due to these political commitments. In section three, I examine the reasons why this connection is not very well-known. I will argue that the political situation in the United States in the aftermath of World War 2 created conditions where it was dangerous to explicitly link scholarly work and politics, and discuss the reasons that Carnap might have had for distancing himself from – or at least de-emphasizing – the political foundations of his views.

- - - - Tuesday, Oct 26, 2021 - - - -

Computational Logic seminar
Tuesday October 26, 2021, 2-4p, Eastern Time US.
For a zoom link, contact Sergei Artemov (sartemov@gc.cuny.edu)
Speaker: Sergei Artemov, Graduate Center CUNY
Title:   On logical foundations of strategic games

Abstract:  In his dissertation of 1950, Nash based his concept of solution to a game on the principles that  "a rational prediction should be unique, that the players should be able to deduce and make use of it." Nash noticed that such a definitive solution is always a Nash Equilibrium (NE). We observe that, for the basic notion of Aumann's rationality, NE, even if it is unique, is not necessarily Nash's definitive solution.  We show that the Iterated Deletion of Strictly Dominated Strategies is a complete procedure for Nash's definitive solution for strategic games.

- - - - Wednesday, Oct 27, 2021 - - - -

- - - - Thursday, Oct 28, 2021 - - - -

- - - - Friday, Oct 29, 2021 - - - -

Set Theory Seminar
Friday, October 29, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Kameryn Williams, Sam Houston State University

Next Week in Logic at CUNY:

- - - - Monday, Nov 1, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Monday, October 25th, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Fedor Pakhomov Ghent University

This is a joint work with Albert Visser. We prove that no consistent finitely axiomatized theory one-dimensionally interprets its own extension with predicative comprehension. This constitutes a result with the flavor of the Second Incompleteness Theorem whose formulation is completely arithmetic-free. Probably the most important novel feature that distinguishes our result from the previous results of this kind is that it is applicable to arbitrary weak theories, rather than to extensions of some base theory. The methods used in the proof of the main result yield a new perspective on the notion of sequential theory, in the setting of forcing-interpretations. https://arxiv.org/abs/2109.02548

Logic and Metaphysics Workshop
Date: Monday, November 1, 4.15-6.15 (NY time)
Thomans M Ferguson (Amsterdam)
The Subject-Matter of Modal Sentences

The framework of topic-sensitive intentional modal operators (TSIMs) described by Berto provides a general platform for representing agents' intentional states of various kinds. For example, a TSIM can model doxastic states, capturing a notion that given the acceptance of antecedent information P, an agent will have a consequent belief Q. Notably, the truth conditions for TSIMs include a subject-matter filter so that the topic of the consequent Q must be "included" within that of the antecedent. To extend the account to languages with richer expressivity thus requires an expanded account of subject-matter. In this talk, I will discuss extending earlier work on the subject-matter of intensional conditionals to the special case of modal sentences whose primary operators are interpreted by possible worlds semantics.

- - - - Tuesday, Nov 2, 2021 - - - -

- - - - Wednesday, Nov 3, 2021 - - - -

- - - - Thursday, Nov 4, 2021 - - - -

- - - - Friday, Nov 5, 2021 - - - -

Set Theory Seminar
Friday, November 5, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Tom Benhamou, Tel Aviv University
Intermediate Prikry-type models, quotients, and the Galvin property

We classify intermediate models of Magidor-Radin generic extensions. It turns out that similar to Gitik Kanovei and Koepke's result, every such intermediate model is of the form  where  is a subsequence of the generic club added by the forcing. The proof uses the Galvin property for normal filters to prove that quotients of some Prikry-type forcings are -c.c. in the generic extension and therefore do not add fresh subsets to . If time permits, we will also present results regarding intermediate models of the Tree-Prikry forcing.

- - - - Other Logic News - - - -

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Damian Głodkowski; The poset of projections in the Calkin algebra, cont.

IMPAN Working Group in Applications of Set Theory
Seminar: Working group in applications of set theory, IMPAN Tuesday, 26.10.2021, 13.30, room 105, Speaker: Damian Głodkowski (IMPAN/MIM UW) Title: "The poset of projections in the Calkin algebra" continuation Abstact: "We will discuss the set-theoretic properties of the poset of projections in the Calkin algebra of the separable Hilbert space, taking into account possible types of maximal well-ordered sequences and maximal antichains. We will show that it is consistent that among the mentioned subsets there are some with cardinality less than continuum and that Martin's axiom implies that all of them have cardinality continuum. We will also discuss relations between the poset of projections and the Boolean algebra P(ω)/Fin. Based on: Wofsey, Eric; P(ω)/fin and projections in the Calkin algebra. Proc. Amer. Math. Soc. 136 (2008), no. 2, 719-726. ". Visit our seminar page which may include some future talks at https://www.impan.pl/~set_theory/Seminar/

## Next CMU math logic seminar (special time)

Carnegie Mellon Logic Seminar
TUESDAY, October 26, 2021 Mathematical logic seminar: 4:30 PM (Eastern), Online, Jason Parker, Brandon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Polymorphic automorphisms and the Picard group ABSTRACT: We investigate the concept of definable, or inner, automorphism in the logical setting of partial Horn theories. The central technical result extends a syntactical characterization of the group of such automorphisms (called the covariant isotropy group) associated with an algebraic theory to the wider class of quasi-equational theories. We apply this characterization to prove that the isotropy group of a strict monoidal category is precisely its Picard group of invertible objects. Furthermore, we obtain an explicit description of the covariant isotropy group of a presheaf category.

## Wednesday seminar

Prague Set Theory Seminar
Dear all, There is no seminar next week (Wednesday October 27th). People are instead advised to participate the Workshop on Generic Structures which takes place in the Institute next week. https://gens.math.cas.cz/ A leaked preliminary schedule of the workshop for Wednesday October 27 (Yugoslav session): 9:00--9:45 Mirna Džamonja: Morass-generic structures 9:45--10:30 Boriša Kuzeljević: Tukey order of directed sets of cofinality ω2 11:15--12:00 Stevo Todorčević: Ramsey degrees of the topological Q 14:15--15:00 Paul Szeptycki: A topological space from a square(κ) sequence related to convergence and cardinal invariants of the Gδ topology Best, David

## Logic Seminar Wed 27 Oct 2021 17:00 hrs at NUS by Mars Yamaleev

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 27 October 2021, 17:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Mars Yamaleev, Kazan Federal University Title: On the Shoare-Stob Theorem URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: In our talk we consider relative enumerability of 2-c.e. Turing degrees in c.e. degrees below them. We focus on an old question which arises from the well-known work of Soare and Stob in 1982. The Soare-Stob theorem says that for any noncomputable low c.e. Turing degree a there exists a non-c.e. Turing degree d which is above a and relative enumerable in a. The question is whether the degree d can always be chosen as 2-c.e. We answer this question by showing that for some a the degree d must be beyond 2-c.e., and discuss the ideas of proof. Also we consider possible generalizations of this result. All results are obtained in a joint work with Arslanov M.M. and Batyrshin I.I.

## UPDATE: This Week in Logic at CUNY

This Week in Logic at CUNY
Hi everyone,

Please note that Friday's Logic Workshop will use the same zoom link usually used for the Set Theory Seminar. For details about obtaining it, see nylogic.github.io

Best,
Jonas

This Week in Logic at CUNY:

- - - - Wednesday, Oct 20, 2021 - - - -

The New York City Category Theory Seminar
Department of Computer Science
Department of Mathematics
The Graduate Center of The City University of New York
New URL:  http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.html
Contact N Yanofsky for zoom info (noson@sci.brooklyn.cuny.edu)
Speaker:     Dan Shiebler, Oxford University.
Date and Time:     Wednesday October 20, 2021, 7:00 - 8:30 PM., on Zoom.
Title:     Out of Sample Generalization with Kan Extensions.

Abstract: A common problem in data science is use this function defined over this small set to generate predictions over that larger set. Extrapolation, interpolation, statistical inference and forecasting all reduce to this problem. The Kan extension is a powerful tool in category theory that generalizes this notion. In this work we explore several applications of Kan extensions to data science.

- - - - Thursday, Oct 21, 2021 - - - -

- - - - Friday, Oct 22, 2021 - - - -

Logic Workshop
Friday, October 22, 2:00-3:30pm
The seminar will take place virtually at 2:00pm US Eastern Standard Time. The zoom link is the same one usually used for the Set Theory Seminar. For details about obtaining it, see nylogic.github.io
Matthias Aschenbrenner, University of Vienna
The elementary theory of maximal Hardy fields

A Hardy field is a differential field of germs at infinity of one-variable differentiable real-valued functions defined on half-lines. Hardy fields appear naturally in model theory and its applications to real analytic geometry and dynamical systems, and also have found uses in computer algebra, ergodic theory, and various other fields of mathematics. I will discuss some optimal extension results for Hardy fields obtained in the last few years, which lead to a description of the theory of maximal Hardy fields and applications to ordinary differential equations. (This is joint work with Lou van den Dries and Joris van der Hoeven.)

Next Week in Logic at CUNY:

- - - - Monday, Oct 25, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 25, 4.15-6.15 (NY time)

Noah Friedman-Biglin (San José State University)
Title: Regrounding the Unworldly: Pluralism and Politics in Carnap’s Philosophy of Logic

Abstract: The locus classicus of logical pluralism – that is, the view that there is more than on logic, properly so called – since the earliest days of analytic philosophy, can be found in Rudolf Carnap’s ‘principle of tolerance’. Clarifying the principle of tolerance is the focus of this first section of this paper. I will argue that the principle should be understood as widely as possible, and thus we will see that Carnap’s tolerance is a very radical view. In section two, I discuss the motivations Carnap had for his pluralism, and argue that they are based in the Vienna Circle’s “Scientific World-Conception” — a platform of philosophical commitments which set the direction for the Circle’s philosophical investigations as well as a program of social change. What emerges from this discussion is the often-ignored relationship between his logical pluralism and his political views. In short, I will argue that the radical quality of his tolerance is due to these political commitments. In section three, I examine the reasons why this connection is not very well-known. I will argue that the political situation in the United States in the aftermath of World War 2 created conditions where it was dangerous to explicitly link scholarly work and politics, and discuss the reasons that Carnap might have had for distancing himself from – or at least de-emphasizing – the political foundations of his views.

Models of Peano Arithmetic (MOPA)
Monday, October 25th, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Fedor Pakhomov Ghent University

- - - - Tuesday, Oct 26, 2021 - - - -

- - - - Wednesday, Oct 27, 2021 - - - -

- - - - Thursday, Oct 28, 2021 - - - -

- - - - Friday, Oct 29, 2021 - - - -

Set Theory Seminar
Friday, October 29, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Kameryn Williams, Sam Houston State University

- - - - Other Logic News - - - -

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Oct 18, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 18, 4.15-6.15 (NY time)

Rohit Parikh (CUNY GC).
Title: States of Knowledge

Abstract: We know from long ago that among a group of people and given a true proposition P, various states of knowledge of P are possible. The lowest is when no one knows P and the highest is when P is common knowledge. The notion of common knowledge is usually attributed to David Lewis, but it was independently discovered by Schiffer. There are indications of it also in the doctoral dissertation of Robert Nozick. Aumann in his celebrated Agreeing to Disagree paper is generally thought to be the person to introduce it into game theory. But what are the intermediate states? It was shown by Pawel Krasucki and myself that there are only countably many and they correspond to what S. C. Kleene called regular sets. But different states of knowledge can cause different group actions. If you prefer restaurant A to B and so do I, and it is common knowledge, and we want to eat together, then we are likely to both go to A. But without that knowledge we might end up in B, or one in A and one in B. This was discussed by Thomas Schelling who also popularized the notion of focal points. Do different states of knowledge always lead to different group actions? Or can there be distinct states which cannot be distinguished through action? The question seems open. It obviously arises when we try to infer the states of knowledge of animals by witnessing their actions. We will discuss the old developments as well as some more recent ideas.

- - - - Tuesday, Oct 19, 2021 - - - -

- - - - Wednesday, Oct 20, 2021 - - - -

The New York City Category Theory Seminar
Department of Computer Science
Department of Mathematics
The Graduate Center of The City University of New York
New URL:  http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.html
Contact N Yanofsky for zoom info (noson@sci.brooklyn.cuny.edu)
Speaker:     Dan Shiebler, Oxford University.
Date and Time:     Wednesday October 20, 2021, 7:00 - 8:30 PM., on Zoom.
Title:     Out of Sample Generalization with Kan Extensions.

Abstract: A common problem in data science is use this function defined over this small set to generate predictions over that larger set. Extrapolation, interpolation, statistical inference and forecasting all reduce to this problem. The Kan extension is a powerful tool in category theory that generalizes this notion. In this work we explore several applications of Kan extensions to data science.

- - - - Thursday, Oct 21, 2021 - - - -

- - - - Friday, Oct 22, 2021 - - - -

Logic Workshop
Friday, October 22, 2:00-3:30pm
The seminar will take place virtually at 2:00pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.orgfor meeting id.
Matthias Aschenbrenner, University of Vienna
The elementary theory of maximal Hardy fields

A Hardy field is a differential field of germs at infinity of one-variable differentiable real-valued functions defined on half-lines. Hardy fields appear naturally in model theory and its applications to real analytic geometry and dynamical systems, and also have found uses in computer algebra, ergodic theory, and various other fields of mathematics. I will discuss some optimal extension results for Hardy fields obtained in the last few years, which lead to a description of the theory of maximal Hardy fields and applications to ordinary differential equations. (This is joint work with Lou van den Dries and Joris van der Hoeven.)

Next Week in Logic at CUNY:

- - - - Monday, Oct 25, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 25, 4.15-6.15 (NY time)

Noah Friedman-Biglin (San José State University)
Title: Regrounding the Unworldly: Pluralism and Politics in Carnap’s Philosophy of Logic

Abstract: The locus classicus of logical pluralism – that is, the view that there is more than on logic, properly so called – since the earliest days of analytic philosophy, can be found in Rudolf Carnap’s ‘principle of tolerance’. Clarifying the principle of tolerance is the focus of this first section of this paper. I will argue that the principle should be understood as widely as possible, and thus we will see that Carnap’s tolerance is a very radical view. In section two, I discuss the motivations Carnap had for his pluralism, and argue that they are based in the Vienna Circle’s “Scientific World-Conception” — a platform of philosophical commitments which set the direction for the Circle’s philosophical investigations as well as a program of social change. What emerges from this discussion is the often-ignored relationship between his logical pluralism and his political views. In short, I will argue that the radical quality of his tolerance is due to these political commitments. In section three, I examine the reasons why this connection is not very well-known. I will argue that the political situation in the United States in the aftermath of World War 2 created conditions where it was dangerous to explicitly link scholarly work and politics, and discuss the reasons that Carnap might have had for distancing himself from – or at least de-emphasizing – the political foundations of his views.

Models of Peano Arithmetic (MOPA)
Monday, October 25th, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Fedor Pakhomov Ghent University

- - - - Tuesday, Oct 26, 2021 - - - -

- - - - Wednesday, Oct 27, 2021 - - - -

- - - - Thursday, Oct 28, 2021 - - - -

- - - - Friday, Oct 29, 2021 - - - -

Set Theory Seminar
Friday, October 29, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Kameryn Williams, Sam Houston State University

- - - - Other Logic News - - - -

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Philip Welch (University of Bristol)
TITLE: The universe constructed from a set (or class) of regular cardinals
DATE: 20 October 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online via Zoom:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609
joan.bagaria@icrea.cat
bagaria@ub.edu

## Damian Głodkowski; The poset of projections in the Calkin algebra

IMPAN Working Group in Applications of Set Theory
Seminar: Working group in applications of set theory, IMPAN Tuesday, 19.10.2021, 13.30, room 105, Speaker: Damian Głodkowski (IMPAN/MIM UW) Title: "The poset of projections in the Calkin algebra" Abstact: "We will discuss the set-theoretic properties of the poset of projections in the Calkin algebra of the separable Hilbert space, taking into account possible types of maximal well-ordered sequences and maximal antichains. We will show that it is consistent that among the mentioned subsets there are some with cardinality less than continuum and that Martin's axiom implies that all of them have cardinality continuum. We will also discuss relations between the poset of projections and the Boolean algebra P(ω)/Fin. Based on: Wofsey, Eric; P(ω)/fin and projections in the Calkin algebra. Proc. Amer. Math. Soc. 136 (2008), no. 2, 719-726. ". Visit our seminar page which may include some future talks at https://www.impan.pl/~set_theory/Seminar/

## Logic Seminar Wed 20 Oct 2021 16:00 hrs at NUS by Yang Yue

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 20 Oct 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Yang Yue, NUS Title: A recursive coloring without Delta-3 solutions for Hindman's Theorem URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: This is a follow up of Liao Yuke's talk last week. I will explain in detail his result which says that there exists a recursive coloring f: N -> {0,1} such that for all infinite subset X of N, if FS(X) is homogeneous for f, then X is not recursive in 0''. Here FS(X) is the set of all finite sums of distinct elements of X. Liao Yuke's result improved Blass, Hirst and Simpson's theorem in 1987 (from no 0' recursive solutions to no 0'' recursive ones).

## (KGRC) seminar talks on Tuesday, October 19 and Thursday, October 21

Kurt Godel Research Center
The KGRC welcomes as guest: Chris Lambie-Hanson (host: Vera Fischer) will visit from October 18 to October 23 and give two talks (see below). * * * Set Theory Research Seminar Kurt Gödel Research Center Tuesday, October 19 "Strongly unbounded subadditive colorings" Chris Lambie-Hanson (Czech Academy of Sciences) Given infinite cardinals $\kappa$ and $\theta$, functions of the form $c:[\kappa]^2 \rightarrow \theta$ exhibiting certain unboundedness properties provide a strong counterexample to the generalization of Ramsey's theorem to $\kappa$ and have seen a wide variety of applications. In this talk, we will discuss the existence of such strongly unbounded colorings, focusing in particular on colorings with subadditivity properties. We will then present some applications to general topology. In particular, building on work of Chen-Mertens and Szeptycki, we will prove that the failure of the Singular Cardinals Hypothesis implies the existence of a Fr\'{e}chet, $\alpha_1$-space whose $G_\delta$-modification has large tightness. This is joint work with Assaf Rinot. Time and Place Talk at 3:00pm, mixed mode (in person as well as via Zoom) Universität Wien Institut für Mathematik Lecture Hall HS 8 1st floor Oskar-Morgenstern-Platz 1 1090 Wien If you want to attend in person, please be aware of the fact that you will be required to show proof of your COVID-19 "2.5G" status (vaccinated, recovered, PCR tested) upon entry of the buildings, or during sporadic random checks in the seminar rooms. During the talk we will also pass around an attendance sheet to facilitate contact tracing. (According to the regulations, this form will be kept for 28 days and destroyed thereafter.) Zoom: This talk will be given in person as well as via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at! * * * Logic Colloquium Kurt Gödel Research Center Thursday, October 21 "Variations on a theorem of Silver" Chris Lambie-Hanson (Czech Academy of Sciences) Shortly after the advent of forcing in the 1960s, Easton proved that, modulo some trivial constraints concerning monotonicity and cofinality, the axioms of set theory place no restrictions on the behavior of exponentiation at regular cardinals. In a surprising turn of events, this turned out not to be the case for singular cardinals, and the last half-century has seen a procession of deep results uncovering nontrivial constraints on exponentiation at singular cardinals. One of the first of these results was Silver's theorem, which in essence states that if $\lambda$ is a singular cardinal of uncountable cofinality and there are "many" singular cardinals $\kappa < \lambda$ such that $2^\kappa = \kappa^+$, then it must also be the case that $2^\lambda = \lambda^+$. In particular, if the Singular Cardinals Hypothesis fails, then it must fail first at a singular cardinal of countable cofinality. We will discuss this seminal theorem and a number of variations thereon, and we will end by sketching a proof of a version of Silver's theorem pertaining to certain generalized cardinal characteristics. Time and Place Talk at 3:00pm, mixed mode (in person as well as via Zoom) Universität Wien Institut für Mathematik Lecture Hall HS 13 2nd floor Oskar-Morgenstern-Platz 1 1090 Wien If you want to attend in person, please be aware of the fact that you will be required to show proof of your COVID-19 "2.5G" status (vaccinated, recovered, PCR tested) upon entry of the buildings, or during sporadic random checks in the seminar rooms. During the talk we will also pass around an attendance sheet to facilitate contact tracing. (According to the regulations, this form will be kept for 28 days and destroyed thereafter.) Zoom: This talk will be given in person as well as via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## Talks next Tuesday

Carnegie Mellon Logic Seminar

## Wednesday seminar

Prague Set Theory Seminar
Dear all, There is no seminar tomorrow Wednesday October 13th. The seminar meets again next week on Wednesday October 20th at 11:00 in the Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building. Program: Noé de Rancourt -- A nonseparable version of Pełczyński's unconditional space, part 2 Abstract: Pełczyński's unconditional space is a well-known example of a separable Banach space having a universal unconditional basis. It can be seen as a Fraïssé limit, and in particular, it has many nontrivial isometries. In a common work in progress with Ziemowit Kostana, we built a nonseparable version of this space in a forcing extension. Surprisingly, unlike its separable counterpart, our space is very rigid. In my last talk, I presented the motivations of this construction and the required preliminaries in Banach space theory. In this second talk, I will concentrate on the actual construction, and the proof of the rigidity properties, namely: - every operator on our space is the sum of a diagonal operator and an operator with separable range; - all onto isometries of our space are trivial. As the first talk was mainly classical preliminaries, this talk will be accessible to those of you who know the basics of Banach space theory (actually, the theory of unconditional bases), even if they haven't attended the first talk. Best, David

## Logic Seminar Wednesday 13 October 2021 16:00 hrs at NUS by Liao Yuke

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 13 October 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Liao Yuke Title: Computable coloring without Pi-3 solution for Hindman's Theorem URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Hindman's theorem is a Ramsey type theorem related to finite sum while its proof-theoretic strength still has a huge gap. One form of the question is that if any computable coloring function would have an arithmetic solution (homogeneous set). We will construct a computable coloring functions that no Pi-3 set can be homogeneous.

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Oct 11, 2021 - - - -

*** GRAD CENTER CLOSED TODAY ***

- - - - Tuesday, Oct 12, 2021 - - - -

Computational Logic Seminar
Tuesday October 12, 2021, 2-4pm
For a zoom link, contact Sergei Artemov (sartemov@gc.cuny.edu)
Speakers:
Rui-Jie Yew, Massachusetts Institute of Technology
Pavel Naumov, University of Southampton, UK
Title: Three Forms of Responsibility in Multiagent Systems

Abstract:  In this talk we define and discuss three distinct forms of responsibility in multiagent systems that have been previously considered in the literature: counterfactual responsibility, responsibility for seeing-to-it, and responsibility for forcing. We show that, in the case of the extensive form games, none of these forms can be defined through the other two. In strategic games, the responsibility for seeing-to-it and the responsibility for forcing are equivalent, and their expressibility through the counterfactual responsibility depends on the technical details of the language and the semantics. Finally, we observe that the ownership and the accountability of one agent for another lead to forms of responsibility different from the three that we studied.

- - - - Wednesday, Oct 13, 2021 - - - -

- - - - Thursday, Oct 14, 2021 - - - -

- - - - Friday, Oct 15, 2021 - - - -

Set Theory Seminar
Friday, October 1
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Yuxin Zhou University of Florida

Let  be a natural number, let  be the hypergraph of isosceles triangles in . Under the axiom of choice, the existence of a countable coloring for  is true for every . Without the axiom of choice, the coloring problems will be hard to answer. We often expect the case that the countable chromatic number of one hypergraph doesn't imply the one for another. With an inaccessible cardinal, there is a model of ZF+DC in which  has countable chromatic number while  has uncountable chromatic number. This result is obtained by a balanced forcing over the symmetric Solovay model.

Next Week in Logic at CUNY:

- - - - Monday, Oct 18, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 4, 4.15-6.15 (NY time)

Rohit Parikh (CUNY GC).
Title: States of Knowledge

Abstract: We know from long ago that among a group of people and given a true proposition P, various states of knowledge of P are possible. The lowest is when no one knows P and the highest is when P is common knowledge. The notion of common knowledge is usually attributed to David Lewis, but it was independently discovered by Schiffer. There are indications of it also in the doctoral dissertation of Robert Nozick. Aumann in his celebrated Agreeing to Disagree paper is generally thought to be the person to introduce it into game theory. But what are the intermediate states? It was shown by Pawel Krasucki and myself that there are only countably many and they correspond to what S. C. Kleene called regular sets. But different states of knowledge can cause different group actions. If you prefer restaurant A to B and so do I, and it is common knowledge, and we want to eat together, then we are likely to both go to A. But without that knowledge we might end up in B, or one in A and one in B. This was discussed by Thomas Schelling who also popularized the notion of focal points. Do different states of knowledge always lead to different group actions? Or can there be distinct states which cannot be distinguished through action? The question seems open. It obviously arises when we try to infer the states of knowledge of animals by witnessing their actions. We will discuss the old developments as well as some more recent ideas.

- - - - Tuesday, Oct 19, 2021 - - - -

- - - - Wednesday, Oct 20, 2021 - - - -

The New York City Category Theory Seminar
Department of Computer Science
Department of Mathematics
The Graduate Center of The City University of New York
New URL:  http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.html
Contact N Yanofsky for zoom info (noson@sci.brooklyn.cuny.edu)
Speaker:     Dan Shiebler, Oxford University.
Date and Time:     Wednesday October 20, 2021, 7:00 - 8:30 PM., on Zoom.
Title:     Out of Sample Generalization with Kan Extensions.

Abstract: A common problem in data science is use this function defined over this small set to generate predictions over that larger set. Extrapolation, interpolation, statistical inference and forecasting all reduce to this problem. The Kan extension is a powerful tool in category theory that generalizes this notion. In this work we explore several applications of Kan extensions to data science.

- - - - Thursday, Oct 21, 2021 - - - -

- - - - Friday, Oct 22, 2021 - - - -

Logic Workshop
Friday, October 22, 2:00-3:30pm
The seminar will take place virtually at 2:00pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Matthias Aschenbrenner, University of Vienna

- - - - Other Logic News - - - -

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## UPDATE - This Week in Logic at CUNY

This Week in Logic at CUNY
Note the addition of Thursday's talk by Yuri Gurevich in the Philog Seminar.

Best,
Jonas

This Week in Logic at CUNY:

- - - - Monday, Oct 4, 2021 - - - -

Penn Logic and Computation Seminar
Monday, October 4, 3:30 pm US Eastern, online
Speaker: Sergei Artemov, CUNY Graduate Center
Title: Missing Proofs and the Provability of Consistency

Abstract: We argue that there is a class of widely used and readily formalizable arithmetical proofs of universal properties which are not accounted for in the traditional unprovability of consistency analysis. On this basis, we offer a mathematical proof of consistency for Peano Arithmetic PA and demonstrate that this proof is formalizable in PA. This refutes the widespread belief that there exists no consistency proof of a system that can be formalized in the system itself. Gödel’s Second Incompleteness theorem yields that PA cannot derive the consistency formula ConPA. This does not interfere with our formalized proof of PA-consistency which is not a derivation of the consistency formula ConPA.

The link will be available by 12 noon on Monday. To get it, contact Andre Scedrov <scedrov@math.upenn.edu> or Sergei Artemov <sartemov@gc.cuny.edu>.

Logic and Metaphysics Workshop
Date: Monday, October 4, 4.15-6.15 (NY time)
Speaker: Yale Weiss (CUNY GC)
Title: Bisemilattice Semantics for Intuitionistic and Relevant Modal Logics

Abstract: In this talk, I consider modal logics extending J (intuitionistic logic) and RMO (sometimes called ‘constructive mingle’). Adapting previous work of Humberstone, all of these systems are given a purely operational bisemilattice semantics and soundness and completeness results are proved. I consider a way of exactly translating each intuitionistic modal system into a relevant modal companion and discuss what, if any, light this sheds on the interpretation of the relevant companions. Various applications are examined (e.g., to developing constructive theories of entailment) and results germane to those applications are proved. I also discuss connections between the present semantic framework and related frameworks, including Fine’s hybrid operational-partial order semantics, inquisitive semantics, and Urquhart’s semilattice semantics.

- - - - Tuesday, Oct 5, 2021 - - - -

Computational Logic Seminar
Tuesday October 5, 2021, 2-4pm
For a zoom link, contact Sergei Artemov (sartemov@gc.cuny.edu)
Speaker: Noson Yanofsky, CUNY
Title: Diagonalization, Fixed Points, and Self-reference

Abstract: Some of the most profound and famous theorems in mathematics and computer science of the past 150 years can simultaneously be seen as a consequence of diagonalization, as a fixed-point theorem, and as an instance of a self-referential paradox. These results include Cantor's theorems about different levels of infinity; Russell's paradox; Gödel's incompleteness theorem; Turing's halting problem; and much more. Amazingly, all these diverse theorems and all viewpoints can be seen as instances of a single simple theorem of basic category theory. We describe this theorem and show some of the instances. A large part of the talk will be a discussion of diagonalization proofs and fixed point theorems that fail to be instances of this categorical theorem. We will meet another categorical idea that unifies some of those instances. No category theory is needed for this talk.

- - - - Wednesday, Oct 6, 2021 - - - -

The New York City Category Theory Seminar
Department of Computer Science
Department of Mathematics
The Graduate Center of The City University of New York
New URL:  http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.html
Contact N Yanofsky for zoom info (noson@sci.brooklyn.cuny.edu)
Speaker:     Gemma De las Cuevas, University of Innsbruck.
Date and Time:     Wednesday October 6, 2021, 7:00 - 8:30 PM., on Zoom.
Title:     From simplicity to universality and undecidability.

Abstract: Why is it so easy to generate complexity? I will suggest that this is due to the phenomenon of universality — essentially every non-trivial system is universal, and thus able to explore all complexity in its domain. We understand universality in spin models, automata and neural networks. I will present the first step toward rigorously linking the first two, where we cast classical spin Hamiltonians as formal languages and classify the latter in the Chomsky hierarchy. We prove that the language of (effectively) zero-dimensional spin Hamiltonians is regular, one-dimensional spin Hamiltonians is deterministic context-free, and higher-dimensional and all-to-all spin Hamiltonians is context-sensitive. I will also talk about the other side of the coin of universality, namely undecidability, and will raise the question of whether universality is visible in Lawvere’s Theorem.

- - - - Thursday, Oct 7, 2021 - - - -

Philog Seminar
Thursday, October 7, 6:30 PM
A Zoom link will be posted  Wednesday on https://philog.arthurpaulpedersen.org/
Negative probabilities: What are they for?
Yuri Gurevich, University of Michigan

The topic may sound nonsensical. The standard frequential interpretation of probabilities makes no sense for negative probabilities. Yet negative probabilities are profitably used in quantum physics and elsewhere. So what are they? What is their intrinsic meaning? We don't know. There are attempts in the literature to provide meaning for negative probabilities but, in our judgement, the problem is wide open.

Instead, we address a more pragmatic question: What are negative probabilities good for? It is not rare in science to use a concept without understanding its intrinsic meaning. Consider early uses of complex numbers. The standard quantitative interpretation of numbers makes no sense for imaginary numbers. And the intrinsic meaning of imaginary numbers wasn't clear (and is debatable even today). Yet complex numbers were profitably used to solve algebraic equations. It turned out, for example, that many real algebraic numbers cannot be
expressed in radicals unless we allow non-real complex coefficients.

It turns out that the disparate quantum applications of negative probabilities can be seen as examples of a certain application template. To make this template explicit, we introduce observation spaces. An observation space S is a family of (nonnegative) probability distributions P1, P2, ... on a common sample space. A question arises whether there is a single probability distribution P (a grounding for S) which yields all P1, P2, ... as marginal distributions. That P may be necessarily signed. We solve the grounding problem for a number of observation spaces of note.

The talk is based on a recent paper with Andreas Blass in J. Phys. A.

- - - - Friday, Oct 8, 2021 - - - -

Set Theory Seminar
Friday, October 8
The seminar will take place virtually at 2:00pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Brent Cody, Virginia Commonwealth University
Higher derived topologies
By beginning with the order topology on an ordinal , and iteratively declaring more and more derived sets to be open, Bagaria defined the derived topologies  on , where  is an ordinal. He showed that the non-isolated points in the space  can be characterized using a strong form of iterated simultaneous stationary reflection called -s-reflection, which is deeply connected to certain transfinite indescribability properties. However, Bagaria's definitions break for  because, under his definitions, the -th derived topology  is discrete and no ordinal  can be -s-stationary. We will discuss some new work in which we use certain diagonal versions of Bagaria's definitions to extend his results. For example, we introduce the notions of diagonal Cantor derivative and use it to obtain a sequence of derived topologies on a regular  that is strictly longer than that of Bagaria's, under certain hypotheses.

Next Week in Logic at CUNY:

- - - - Monday, Oct 11, 2021 - - - -

- - - - Tuesday, Oct 12, 2021 - - - -

- - - - Wednesday, Oct 13, 2021 - - - -

- - - - Thursday, Oct 14, 2021 - - - -

- - - - Friday, Oct 15, 2021 - - - -

Set Theory Seminar
Friday, October 1
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Yuxin Zhou University of Florida

- - - - Other Logic News - - - -

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Oct 4, 2021 - - - -

Penn Logic and Computation Seminar
Monday, October 4, 3:30 pm US Eastern, online
Speaker: Sergei Artemov, CUNY Graduate Center
Title: Missing Proofs and the Provability of Consistency

Abstract: We argue that there is a class of widely used and readily formalizable arithmetical proofs of universal properties which are not accounted for in the traditional unprovability of consistency analysis. On this basis, we offer a mathematical proof of consistency for Peano Arithmetic PA and demonstrate that this proof is formalizable in PA. This refutes the widespread belief that there exists no consistency proof of a system that can be formalized in the system itself. Gödel’s Second Incompleteness theorem yields that PA cannot derive the consistency formula ConPA. This does not interfere with our formalized proof of PA-consistency which is not a derivation of the consistency formula ConPA.

The link will be available by 12 noon on Monday. To get it, contact Andre Scedrov <scedrov@math.upenn.edu> or Sergei Artemov <sartemov@gc.cuny.edu>.

Logic and Metaphysics Workshop
Date: Monday, October 4, 4.15-6.15 (NY time)
Speaker: Yale Weiss (CUNY GC)
Title: Bisemilattice Semantics for Intuitionistic and Relevant Modal Logics

Abstract: In this talk, I consider modal logics extending J (intuitionistic logic) and RMO (sometimes called ‘constructive mingle’). Adapting previous work of Humberstone, all of these systems are given a purely operational bisemilattice semantics and soundness and completeness results are proved. I consider a way of exactly translating each intuitionistic modal system into a relevant modal companion and discuss what, if any, light this sheds on the interpretation of the relevant companions. Various applications are examined (e.g., to developing constructive theories of entailment) and results germane to those applications are proved. I also discuss connections between the present semantic framework and related frameworks, including Fine’s hybrid operational-partial order semantics, inquisitive semantics, and Urquhart’s semilattice semantics.

- - - - Tuesday, Oct 5, 2021 - - - -

Computational Logic Seminar
Tuesday October 5, 2021, 2-4pm
For a zoom link, contact Sergei Artemov (sartemov@gc.cuny.edu)
Speaker: Noson Yanofsky, CUNY
Title: Diagonalization, Fixed Points, and Self-reference

Abstract: Some of the most profound and famous theorems in mathematics and computer science of the past 150 years can simultaneously be seen as a consequence of diagonalization, as a fixed-point theorem, and as an instance of a self-referential paradox. These results include Cantor's theorems about different levels of infinity; Russell's paradox; Gödel's incompleteness theorem; Turing's halting problem; and much more. Amazingly, all these diverse theorems and all viewpoints can be seen as instances of a single simple theorem of basic category theory. We describe this theorem and show some of the instances. A large part of the talk will be a discussion of diagonalization proofs and fixed point theorems that fail to be instances of this categorical theorem. We will meet another categorical idea that unifies some of those instances. No category theory is needed for this talk.

- - - - Wednesday, Oct 6, 2021 - - - -

The New York City Category Theory Seminar
Department of Computer Science
Department of Mathematics
The Graduate Center of The City University of New York
New URL:  http://www.sci.brooklyn.cuny.edu/~noson/Seminar/index.html
Contact N Yanofsky for zoom info (noson@sci.brooklyn.cuny.edu)
Speaker:     Gemma De las Cuevas, University of Innsbruck.
Date and Time:     Wednesday October 6, 2021, 7:00 - 8:30 PM., on Zoom.
Title:     From simplicity to universality and undecidability.

Abstract: Why is it so easy to generate complexity? I will suggest that this is due to the phenomenon of universality — essentially every non-trivial system is universal, and thus able to explore all complexity in its domain. We understand universality in spin models, automata and neural networks. I will present the first step toward rigorously linking the first two, where we cast classical spin Hamiltonians as formal languages and classify the latter in the Chomsky hierarchy. We prove that the language of (effectively) zero-dimensional spin Hamiltonians is regular, one-dimensional spin Hamiltonians is deterministic context-free, and higher-dimensional and all-to-all spin Hamiltonians is context-sensitive. I will also talk about the other side of the coin of universality, namely undecidability, and will raise the question of whether universality is visible in Lawvere’s Theorem.

- - - - Thursday, Oct 7, 2021 - - - -

- - - - Friday, Oct 8, 2021 - - - -

Set Theory Seminar
Friday, October 8
The seminar will take place virtually at 2:00pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Brent Cody, Virginia Commonwealth University
Higher derived topologies
By beginning with the order topology on an ordinal , and iteratively declaring more and more derived sets to be open, Bagaria defined the derived topologies  on , where  is an ordinal. He showed that the non-isolated points in the space  can be characterized using a strong form of iterated simultaneous stationary reflection called -s-reflection, which is deeply connected to certain transfinite indescribability properties. However, Bagaria's definitions break for  because, under his definitions, the -th derived topology  is discrete and no ordinal  can be -s-stationary. We will discuss some new work in which we use certain diagonal versions of Bagaria's definitions to extend his results. For example, we introduce the notions of diagonal Cantor derivative and use it to obtain a sequence of derived topologies on a regular  that is strictly longer than that of Bagaria's, under certain hypotheses.

Next Week in Logic at CUNY:

- - - - Monday, Oct 11, 2021 - - - -

- - - - Tuesday, Oct 12, 2021 - - - -

- - - - Wednesday, Oct 13, 2021 - - - -

- - - - Thursday, Oct 14, 2021 - - - -

- - - - Friday, Oct 15, 2021 - - - -

Set Theory Seminar
Friday, October 1
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Yuxin Zhou University of Florida

- - - - Other Logic News - - - -

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## (KGRC) Set Theory Research Seminar talk on Tuesday, October 5

Kurt Godel Research Center
The KGRC welcomes as guest: Vladimir Tkachuk (host: Vera Fischer) will visit from October 3 to October 6 and give a talk (see below). * * * Set Theory Research Seminar Kurt Gödel Research Center Tuesday, October 5 "Exponential domination and its bidual in function spaces" Vladimir Tkachuk (Universidad Autonoma Metropolitana, Mexico City, Mexico) Given an infinite cardinal \kappa, we say that a space X features exponential \kappa-domination if every set A \subset X with |A| \leq 2^\kappa is contained in the closure of a set of cardinality \leq \kappa. Evidently, every space X of density not exceeding \kappa features exponential \kappa-domination. We will show that spaces with exponential \kappa-domination constitute a class with nice categorical properties and, in Cech-complete spaces, exponential \kappa-domination coincides with density \leq \kappa. Another merit of exponential \kappa-domination is that it has a bidual in function spaces. To show this, we will introduce exponential \kappa-cofinality and prove that X is exponentially \kappa-cofinal if and only if Cp(X) features exponential \kappa-domination and X is a space with exponential \kappa-domination if and only if Cp(X) is exponentially \kappa-cofinal. Time and Place Talk at 3:00pm, in person Universität Wien Institut für Mathematik Lecture Hall HS 8 1st floor Oskar-Morgenstern-Platz 1 1090 Wien Please be aware of the fact that you may be required to show proof of your 3G status upon entry of the buildings, or during sporadic random checks in the seminar rooms. During the Logic Colloquium we will also pass around an attendance sheet to facilitate contact tracing. (According to the regulations, this form will be kept for 28 days and destroyed thereafter.)

## Two events on October 5

Carnegie Mellon Logic Seminar
TUESDAY, October 5, 2021 Mathematical logic seminar: 3:30 P.M., Online, Jindra Zapletal, University of Florida Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Set theory of algebraic hypergraphs ABSTRACT: I explain the main aim of the geometric set theory program: obtaining a careful calibration of Sigma two one sentences (typically, consequences of the axiom of choice) in choiceless set theory. As a specific class of such sentences, I consider the countable chromatic number of various (sigma-)algebraic hypergraphs on Euclidean spaces. A recent result deals with the graph G_n connecting points of rational distance in R^n: for every n>0, it is consistent with ZF+DC that the chromatic number of G_n is countable while that of G_{n+1} is not. TUESDAY, October 5, 2021 Set Theory Reading Group: 4:30 P.M., Online, Yuxin Zhou, University of Florida Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Distinguish coloring problems for isosceles triangle in R^2 and R^3 ABSTRACT: For n a positive natural number, let Γn be the hypergraph of isosceles triangles in R^n. Under the axiom of choice, the existence of a countable coloring for Γn is true for every n. Without the axiom of choice, the coloring problems will be hard to answer. With the existence of the inaccessible cardinal assumption, there is a model of ZF+DC in which Γ2 has countable chromatic number while Γ3 has uncountable chromatic number. This result is obtained by forcing over the symmetric Solovay model.

## Wednesday seminar

Prague Set Theory Seminar
Dear all, The seminar meets on Wednesday October 6th at 11:00 in the Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building. Program: Noé de Rancourt -- A nonseparable version of Pełczyński's unconditional space Abstract: Pełczyński's unconditional space is a well-known example of a separable Banach space having a universal unconditional basis. It can be seen as a Fraïssé limit, and in particular, it has many nontrivial isometries. In a common work in progress with Ziemowit Kostana, we built a nonseparable version of this space in a forcing extension. Surprisingly, unlike its separable counterpart, our space is very rigid. In this talk, I will explain the construction of this space, show that it has few operators, and that all of its isometries are trivial. I will not assume any knowledge in Banach space theory, apart from a vague idea of what a Banach space is. The construction and the proofs I will present rely on almost no prerequisites in functional analysis, so I will be able to introduce everything during the talk. Best, David

## Logic Seminar 6 Oct 2021 16:00 hrs at NUS by Chong Chitat

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 6 October 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Chong Chitat Title: First-order strength of tree colorings Abstract: In this talk we discuss the proof-theoretic strength, from the reverse mathematics perspective, of combinatorial principles concerning the coloring of binary trees and finite products of binary trees. Beginning with the principle TT^1, which states that every finite coloring of the full binary tree has an isomorphic monochromatic subtree, we will cover its strengthening to the existence of a strong monochromatic subtree, and to the full generalization of the latter known as the Halpern-Laeuchli Theorem. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## This Week in Logic at CUNY - UPDATE

This Week in Logic at CUNY
Hi everyone,

Please see the addition of tomorrow's (Tuesday 9/28) talk in the Computational Logic Seminar.

Best,
Jonas

This Week in Logic at CUNY:

- - - - Tuesday, Sep 28, 2021 - - - -

Computational Logic Seminar
Tuesday September 28, 2021, 2-4pm
For a zoom link, contact Sergei Artemov (sartemov@gc.cuny.edu)
Speaker: Melvin Fitting, CUNY Graduate Center

Abstract.  Classical logic is almost always formulated with the empty domain not allowed.  Still, we do understand quantification over the empty domain.  So why the discrepancy?  Allowing the empty domain was investigated axiomatically by a couple of well-known people in the 1950’s and 1960’s, but this had no real effect.  It turns out there are two versions of what is called “Inclusive” logic, allowing the empty domain.  I looked at this using tableaus, 50 years ago, and found that the difference between the two versions was easy to understand with tableau machinery.  Recently I went back and looked at the work again, and found that the two versions actually differ on interpolation.  One version has interpolants, the other doesn’t.  A curious result, certainly..

This talk is about classical logic.  But the same issues come up for intuitionistic logic, modal logics, paraconsistent logics, and so on.  Nobody seems to have looked at what happens.  At the heart of it all, the original question that prompted the investigations of the 1960’s still remains: why should the existence of something be taken as a logical truth?

- - - - Wednesday, Sep 29, 2021 - - - -

- - - - Thursday, Sep 30, 2021 - - - -

- - - - Friday, Oct 01, 2021 - - - -

Set Theory Seminar
Friday, October 1
The seminar will take place virtually at 11:30am US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Matteo Viale, University of Torino
Absolute model companionship, forcibility, and the continuum problem: Part II

Absolute model companionship (AMC) is a strengthening of model companionship defined as follows: For a theory  denotes the logical consequences of  which are boolean combinations of universal sentences.  is the AMC of  if it is model complete and . The -theory  of algebraically closed field is the model companion of the theory of  but not its AMC as . Any model complete theory  is the AMC of . We use AMC to study the continuum problem and to gauge the expressive power of forcing. We show that (a definable version of)  is the unique solution to the continuum problem which can be in the AMC of a partial Morleyization of the -theory there are class many supercompact cardinals. We also show that (assuming large cardinals) forcibility overlaps with the apparently weaker notion of consistency for any mathematical problem  expressible as a -sentence of a (very large fragment of) third order arithmetic (, the Suslin hypothesis, the Whitehead conjecture for free groups are a small sample of such problems ). Partial Morleyizations can be described as follows: let  be the set of first order -formulae; for  is the expansion of  adding atomic relation symbols  for all formulae  in  and  is the -theory asserting that each -formula  is logically equivalent to the corresponding atomic formula . For a -theory   is the partial Morleyization of  induced by .

Next Week in Logic at CUNY:

- - - - Monday, Oct 4, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 4, 4.15-6.15 (NY time)

- - - - Tuesday, Oct 5, 2021 - - - -

- - - - Wednesday, Oct 6, 2021 - - - -

- - - - Thursday, Oct 7, 2021 - - - -

- - - - Friday, Oct 8, 2021 - - - -

Set Theory Seminar
Friday, October 8
The seminar will take place virtually at 2:00pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Brent Cody, Virginia Commonwealth University
Higher derived topologies

- - - - Other Logic News - - - -

ANNOUNCEMENT - Carl Posy - Working Group on Intuitionism

I am assembling a working group on intuitionism.  We aim eventually to explore the philosophical ground of intuitionistic mathematics.  We will ultimately look at issues in philosophy of mind (including phenomenology), epistemology, ontology and semantics. However, in order to do so, we will begin with in depth studies of intuitionistic mathematics and intuitionistic logic.

Participation in the group will provide the needed background for someone who would like to develop large or small projects related to some aspect of intuitionism (mathematics, logic or philosophy).  The group will also serve those who are interested simply in acquiring a working knowledge of intuitionism per se.

Our initial studies of intuitionistic mathematics and logic will roughly follow the organization of the first chapters of my recent book Mathematical Intuitionism.  However, we will refine, correct and expand the material in the book.  There’ll be references and material for those who would like to pursue some topic or other even further.

The group invites both participants with some limited or even extensive background in intuitionism and those without any background in intuitionism but with an interest in learning about intuitionism and/or working on related research aims.  Some knowledge of mathematics (in particular of elementary real analysis) and/or logic (in particular through basic philosophical logic) is desirable.

The group will have regularly scheduled meetings no more frequently than twice a month, during the academic year.  We will set a schedule at the start of each year.

The current plan is to function for at least two or three academic years.  Sometime in the second or third year we will have a conference including members and outside researchers. We will begin in late 2021 or early 2022.

From time to time will also have guest lectures from prominent researchers.

From time to time active members will  prepare and present material  -- appropriate to their background and interests.

Anyone interested should contact me at:  carl.posy@mail.huji.ac.il    We will then arrange a time to speak.

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## This Week in Logic at CUNY

This Week in Logic at CUNY
Hi everyone,

Apologies for the late start this semester.  Regular weekly mailings of "This Week in Logic" will continue going forward - please send me your announcements for upcoming New York logic events.  Welcome back!

Best,
Jonas

This Week in Logic at CUNY:

- - - - Monday, Sep 27, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, September 27, 4.15-6.15 (NY time)
Speaker: Rashed Ahmad (University of Connecticut)
Title: A Recipe for Paradox: A Better Schema than the Inclosure Schema

- - - - Tuesday, Sep 28, 2021 - - - -

- - - - Wednesday, Sep 29, 2021 - - - -

- - - - Thursday, Sep 30, 2021 - - - -

- - - - Friday, Oct 01, 2021 - - - -

Set Theory Seminar
Friday, October 1
The seminar will take place virtually at 11:30am US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Matteo Viale, University of Torino
Absolute model companionship, forcibility, and the continuum problem: Part II

Absolute model companionship (AMC) is a strengthening of model companionship defined as follows: For a theory  denotes the logical consequences of  which are boolean combinations of universal sentences.  is the AMC of  if it is model complete and . The -theory  of algebraically closed field is the model companion of the theory of  but not its AMC as . Any model complete theory  is the AMC of . We use AMC to study the continuum problem and to gauge the expressive power of forcing. We show that (a definable version of)  is the unique solution to the continuum problem which can be in the AMC of a partial Morleyization of the -theory there are class many supercompact cardinals. We also show that (assuming large cardinals) forcibility overlaps with the apparently weaker notion of consistency for any mathematical problem  expressible as a -sentence of a (very large fragment of) third order arithmetic (, the Suslin hypothesis, the Whitehead conjecture for free groups are a small sample of such problems ). Partial Morleyizations can be described as follows: let  be the set of first order -formulae; for  is the expansion of  adding atomic relation symbols  for all formulae  in  and  is the -theory asserting that each -formula  is logically equivalent to the corresponding atomic formula . For a -theory   is the partial Morleyization of  induced by .

Next Week in Logic at CUNY:

- - - - Monday, Oct 4, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, October 4, 4.15-6.15 (NY time)

- - - - Tuesday, Oct 5, 2021 - - - -

- - - - Wednesday, Oct 6, 2021 - - - -

- - - - Thursday, Oct 7, 2021 - - - -

- - - - Friday, Oct 8, 2021 - - - -

Set Theory Seminar
Friday, October 8
The seminar will take place virtually at 2:00pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Brent Cody, Virginia Commonwealth University
Higher derived topologies

- - - - Other Logic News - - - -

ANNOUNCEMENT - Carl Posy - Working Group on Intuitionism

I am assembling a working group on intuitionism.  We aim eventually to explore the philosophical ground of intuitionistic mathematics.  We will ultimately look at issues in philosophy of mind (including phenomenology), epistemology, ontology and semantics. However, in order to do so, we will begin with in depth studies of intuitionistic mathematics and intuitionistic logic.

Participation in the group will provide the needed background for someone who would like to develop large or small projects related to some aspect of intuitionism (mathematics, logic or philosophy).  The group will also serve those who are interested simply in acquiring a working knowledge of intuitionism per se.

Our initial studies of intuitionistic mathematics and logic will roughly follow the organization of the first chapters of my recent book Mathematical Intuitionism.  However, we will refine, correct and expand the material in the book.  There’ll be references and material for those who would like to pursue some topic or other even further.

The group invites both participants with some limited or even extensive background in intuitionism and those without any background in intuitionism but with an interest in learning about intuitionism and/or working on related research aims.  Some knowledge of mathematics (in particular of elementary real analysis) and/or logic (in particular through basic philosophical logic) is desirable.

The group will have regularly scheduled meetings no more frequently than twice a month, during the academic year.  We will set a schedule at the start of each year.

The current plan is to function for at least two or three academic years.  Sometime in the second or third year we will have a conference including members and outside researchers. We will begin in late 2021 or early 2022.

From time to time will also have guest lectures from prominent researchers.

From time to time active members will  prepare and present material  -- appropriate to their background and interests.

Anyone interested should contact me at:  carl.posy@mail.huji.ac.il    We will then arrange a time to speak.

- - - - Web Site - - - -

Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Two events on Tuesday 9/28/21

Carnegie Mellon Logic Seminar
TUESDAY, September 28, 2021 Mathematical logic seminar: 3:30 P.M., Online, Thomas Gilton, University of Pittsburgh Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: The tension between reflection/compactness and rigidity in combinatorial set theory ABSTRACT: The aim of this talk is to provide background with which to motivate a recent joint result of the speaker with Omer Ben-Neria. This result concerns the tension between two classes of combinatorial principles in set theory, namely reflection/compactness principles on the one hand and incompactness/anti-reflection properties on the other. The rigidity implied by the latter class often suffices to prove the negation of principles in the former class, and as a result, a large research program in set theory is dedicated to investigating when principles from these two classes are jointly consistent. Our theorem - that the Special Aronszajn Tree Property is consistent with Club Stationary Reflection on $\omega_2$ - is such a result. We will discuss this tension historically before showing how, in our result, the tension shows up in our proof, especially in the radically different properties of our posets which we have to maintain throughout the course of our construction. TUESDAY, September 28, 2021 Set Theory Reading Group: 4:30 P.M., Online, Thomas Gilton, University of Pittsburgh Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Club stationary reflection and the special Aronszajn tree property ABSTRACT: In this talk, we will dive into the technical details of our result with Omer Ben-Neria. We will first show how to specialize trees on $\omega_2$ with a preparatory forcing which is no longer $\kappa$-c.c., as in the classic setting of Laver and Shelah. Rather, this preparatory forcing will satisfy a kind of $\kappa$-strong properness which is witnessed by continuous residue functions like those used in various side conditions iteration theorems of Itay Neeman. We then show how to build posets satisfying this kind of $\kappa$-strong properness by following a Levy collapse of a weakly compact with a class of posets we call $\mathcal{F}_{WC}$-completely proper, where $\mathcal{F}_{WC}$ is the weakly compact filter. This is similar to Abraham's use of guiding reals to obtain strong properness for countable models. We then close by gesturing to solutions of the technical problems which remain, particularly ones involving new preservation theorems for Aronszajn trees and stationary sets.

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Zhixing You (Universitat de Barcelona)
TITLE:
DATE: 29 September 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online via Zoom:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609
joan.bagaria@icrea.cat
bagaria@ub.edu

## Event Tuesday, September 21

Carnegie Mellon Logic Seminar
TUESDAY, September 21, 2021 Set Theory Reading Group: 4:30 P.M., Online, Allison Wang, Carnegie Mellon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Hyperfiniteness and Ramsey notions of largeness ABSTRACT: The lowest non-trivial complexity class in the theory of Countable Borel Equivalence Relations (CBERs) is the class of hyperfinite CBERs. One difficulty that arises in studying this class is determining which CBERs are hyperfinite. Measure theory can be used to answer this question, but not many techniques can. For instance, a Baire category approach cannot distinguish hyperfinite CBERS: a result of Hjorth and Kechris states that every CBER on a Polish space is hyperfinite when restricted to some comeager set. We will discuss a classical proof of Mathias's theorem that every CBER on the Ellentuck Ramsey space is hyperfinite when restricted to some pure Ellentuck cube. Mathias's theorem implies that a Ramsey-theoretic approach also cannot distinguish hyperfinite CBERs. This is joint work with Aristotelis Panagiotopoulos. ORGANIZER'S NOTE: The talk will start after some socializing, at around 4:40 or 4:45.

## Wednesday seminar

Prague Set Theory Seminar
Dear all, We will restart the Wednesday seminar again this autumn. Hopefully we will not need pause it because of the pandemic again. The seminar should meet at the usual time and place, starting on Wednesday September 29. Please let me know in case you would know any email addresses I should add to the mailing list, or in case you would like to be removed from the list. The seminar meets on Wednesday September 29th at 11:00 in the Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building. Program: Chris Lambie Hanson -- Strongly unbounded functions and productivity of chain conditions We discuss the existence of strongly unbounded functions on pairs of ordinals, which provide strong counterexamples to generalizations of Ramsey's theorem to uncountable cardinals. The talk will include a brief, gentle introduction to Todorcevic's powerful technique of walks on ordinals and an application to the infinite productivity of the $\kappa$-Knaster property. Some of the results are joint work with Assaf Rinot. Best, David

## Logic Seminar Wed 15 Sept 2021 16:00 hrs at NUS by Bakhadyr Khoussainov

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 15 September 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Bakhadyr Khoussainov, UESTC, Chengdu and The University of Auckland Title: Probability Structures URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: This talk belongs to the area of probabilistic logic semantics. The first contribution of this work is the introduction of probability structures. Probability structures are the algebraic structures equipped with probability functions on the domains and the atomic predicates. These structures extend type 1 probability structures introduced by Halpern and Bacchus. Type 1 probability structures contain probability functions on domains only. Our probability structures possess an additional statistical knowledge, - probability functions on atomic predicates. We present a method that builds probability spaces for the first order logic formulas and prove that our semantics is sound. The second contribution of this work is the introduction of smooth probability structures. The smooth probability structures carefully refine probability structures so that we have a better control of the probability spaces defined by first order logic formulas. For these structures we initiate the study of first order probability logic (FOPLS), investigate axiomatizability of FOPLS, and address decidability and undecidability questions of the sets of valid formulas. We also study a few algorithmic questions on probability structures.

## Logic Seminar Today 16:00 hrs SGT at NUS by Khoussainov and Stephan

NUS Logic Seminar
Hello, the password of this reminder was wrong, here the amended version. Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 8 September 2021, 16:00 hrs, Singapore Time Zone (GMT+8 hrs) Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Bakhadyr Khoussainov and Frank Stephan Title: Parity Games - Background and Algorithms. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Parity games are games where a marker is moved on a finite graph and each node is annotated with a natural number; the game runs forever and the largest number in an infinitely often visited node decides the winner, if it is even then player Anke wins else player Boris wins. Marcin Jurdzinski showed that this game is in UP intersected coUP and also provided the first not fully exponential algorithm for it; however, the exact time complexity remained unresolved. In 2017, Calude, Jain, Khoussainov, Li and Stephan found a quasipolynomial time algorithm which Jurdzinski and Lazic as well as Fearnley, Jain, Schewe, Stephan and Wojtczak improved the algorithm to be in polynomial space as well as quasipolynomial time. The talk provides the way this algorithm was found and the implications it has for the fixed-parameter-tracktability of parity games and related problems like coloured Muller games. Though now quite a number of quasipolynomial time algorithms are known and there is quite extensive research in this topic, the question on whether parity games can even be solved in polynomial time is still unresolved. This talk is given by Bakhadyr Khoussainov and Frank Stephan jointly also on behalf of their coauthors Cristian Calude, Sanjay Jain and Wei Li.

## Logic Seminar Today 16:00 hrs SGT at NUS by Khoussainov and Stephan

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 8 September 2021, 16:00 hrs, Singapore Time Zone (GMT+8 hrs) Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=3DUWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=3Dx3+y3 Speaker: Bakhadyr Khoussainov and Frank Stephan Title: Parity Games - Background and Algorithms. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Parity games are games where a marker is moved on a finite graph and each node is annotated with a natural number; the game runs forever and the largest number in an infinitely often visited node decides the winner, if it is even then player Anke wins else player Boris wins. Marcin Jurdzinski showed that this game is in UP intersected coUP and also provided the first not fully exponential algorithm for it; however, the exact time complexity remained unresolved. In 2017, Calude, Jain, Khoussainov, Li and Stephan found a quasipolynomial time algorithm which Jurdzinski and Lazic as well as Fearnley, Jain, Schewe, Stephan and Wojtczak improved the algorithm to be in polynomial space as well as quasipolynomial time. The talk provides the way this algorithm was found and the implications it has for the fixed-parameter-tracktability of parity games and related problems like coloured Muller games. Though now quite a number of quasipolynomial time algorithms are known and there is quite extensive research in this topic, the question on whether parity games can even be solved in polynomial time is still unresolved. This talk is given by Bakhadyr Khoussainov and Frank Stephan jointly also on behalf of their coauthors Cristian Calude, Sanjay Jain and Wei Li.

## Logic Seminar 8 September 2021 16:00 hrs at NUS by Bakhadyr Khoussainov and Frank Stephan

NUS Logic Seminar
Hello, there is a typing error in the below email. It should be "8 September 2021", so Wednesday next week. Frank Stephan On Thu, Sep 02, 2021 at 11:18:49PM +0800, Frank STEPHAN wrote: > Invitation to the Logic Seminar at the National University of Singapore > > Date: Wednesday, CORRECTED TO 08 Sep 2021, 16:00 hrs > > Talk via Zoom: > https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 > Meeting ID: 830 4925 8042 > Passcode: 1729=x3+y3 > > Speaker: Bakhadyr Khoussainov and Frank Stephan > > Title: Parity Games - Background and Algorithms. > > URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html > > Abstract: > Parity games are games where a marker is moved on > a finite graph and each node is annotated with a > natural number; the game runs forever and the largest > number in an infinitely often visited node decides > the winner, if it is even then player Anke wins > else player Boris wins. Marcin Jurdzinski showed > that this game is in UP intersected coUP and also > provided the first not fully exponential algorithm > for it; however, the exact time complexity remained > unresolved. In 2017, Calude, Jain, Khoussainov, Li > and Stephan found a quasipolynomial time algorithm > which Jurdzinski and Lazic as well as Schewe and his > collaborators improved to be in polynomial space > as well. The talk provides the way this algorithm > was found and the implications it has for the > fixed-parameter-tracktability of parity games and > related problems like coloured Muller games. Though > now quite a number of quasipolynomial time algorithms > are known and there is quite extensive research in this > topic, the question on whether parity games can even > be solved in polynomial time is still unresolved. > > This talk is given by Bakhadyr Khoussainov and > Frank Stephan jointly also on behalf of their coauthors > Cristian Calude, Sanjay Jain and Wei Li. >

## Logic Seminar 8 September 2021 16:00 hrs at NUS by Bakhadyr Khoussainov and Frank Stephan

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 11 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Bakhadyr Khoussainov and Frank Stephan Title: Parity Games - Background and Algorithms. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Parity games are games where a marker is moved on a finite graph and each node is annotated with a natural number; the game runs forever and the largest number in an infinitely often visited node decides the winner, if it is even then player Anke wins else player Boris wins. Marcin Jurdzinski showed that this game is in UP intersected coUP and also provided the first not fully exponential algorithm for it; however, the exact time complexity remained unresolved. In 2017, Calude, Jain, Khoussainov, Li and Stephan found a quasipolynomial time algorithm which Jurdzinski and Lazic as well as Schewe and his collaborators improved to be in polynomial space as well. The talk provides the way this algorithm was found and the implications it has for the fixed-parameter-tracktability of parity games and related problems like coloured Muller games. Though now quite a number of quasipolynomial time algorithms are known and there is quite extensive research in this topic, the question on whether parity games can even be solved in polynomial time is still unresolved. This talk is given by Bakhadyr Khoussainov and Frank Stephan jointly also on behalf of their coauthors Cristian Calude, Sanjay Jain and Wei Li.

## Logic Seminar today 16:00 hrs at NUS by Rupert Hoelzl, University of the Bundeswehr in Munich

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 1 September 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Rupert Hoelzl Title: The reverse mathematics of inductive inference URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: We investigates inductive inference from the perspective of reverse mathematics. Reverse mathematics is a framework that allows gauging the proof strength of theorems and axioms in many areas of mathematics. We apply its methods to basic notions of algorithmic learning theory such as Angluin's tell-tale criterion and its variants for learning in the limit and for conservative learning, as well as to the more general scenario of partial learning. These notions are studied in the reverse mathematics context for uniformly and weakly represented families of languages. The results are stated in terms of axioms referring to induction strength and to domination of weakly represented families of functions.

## Free Registration for IPEC 2021 until 29 August 2021 (Online Conference)

NUS Logic Seminar
Hello, Most likely on 8 September 2021, Bakhadyr Khoussainov and Frank Stephan will give an invited talk about the paper Deciding parity games in quasipolynomial time by Cristian Calude, Sanjay Jain, Bakhadyr Khoussainov, Wei Li and Frank Stephan from STOC 2017 and SIAM Journal on Computing at IPEC 2021. You can up to tomorrow (29 August 2021) register for free at this online occurring conference through the webpage http://algo2021.tecnico.ulisboa.pt/index.html#registration and information on the conference IPEC is on http://algo2021.tecnico.ulisboa.pt/IPEC2021/index.html The exact programme is not yet there, but will most likely be made available after tomorrow's free registration deadline for nonpresenting participants. IPEC is an International Symposium on Parameterised and Exact Computation. Sorry for the short notice, I was waiting for info about the conference going onto the webpage before sending this. Best regards, Frank

## Felix Weilacher on Tuesday (8/31) 3:30 PM Eastern

Carnegie Mellon Logic Seminar
TUESDAY, August 31 2021 Mathematical logic seminar: 3:30 P.M., Online, Felix Weilacher, Carnegie Mellon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Borel Edge Colorings for Finite Dimensional Groups ABSTRACT: In Borel graph combinatorics, one often produces a structure (e.g. a coloring) by dividing a graph into subgraphs with finite connected components, then defining the structure on those components via some straightforward uniformization result. We first give an overview of some recent work formalizing these notions and applying them to various problems. We then present our own application to the problem of edge coloring. For Borel actions of certain groups, we find "degree plus one" Borel edge colorings, matching the classical bound of Vizing. Furthermore, for finitely generated abelian groups, we are able to exactly determine Borel edge chromatic numbers.

## Logic Seminar 1 Sept 2021 16:00 hrs at NUS by Rupert Hoelzl, Univ. of the Bundeswehr, Munich

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 1 September 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Rupert Hoelzl Title: The reverse mathematics of inductive inference URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html We investigates inductive inference from the perspective of reverse mathematics. Reverse mathematics is a framework that allows gauging the proof strength of theorems and axioms in many areas of mathematics. We apply its methods to basic notions of algorithmic learning theory such as Angluin's tell-tale criterion and its variants for learning in the limit and for conservative learning, as well as to the more general scenario of partial learning. These notions are studied in the reverse mathematics context for uniformly and weakly represented families of languages. The results are stated in terms of axioms referring to induction strength and to domination of weakly represented families of functions.

## Logic Seminar 25 April 2021 16:00 hrs by Ng Keng Meng (NTU) at NUS (today)

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 25 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Ng Keng Meng Title: Are the rationals dense Abstract: There has been a recent revival in the interest in sub-computable mathematics. One of these approaches is to consider primitive recursive'' or punctual structures. This has led to a greater understanding in the effective content of well-known objects and proofs in classical computability theory. When considering the punctual anaologies of classical computabilitiy we often obtain strange and surprising results. I will discuss some recent work in progress in this area, focussing particularly on structural results. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## RIMS Set Theory Workshop: October 12-15, 2021

Conference
RIMS SET THEORY WORKSHOP 2021 Announcement / Call for Contributions RIMS workshop "Recent Developments in Set Theory of the Reals" Date: Tuesday, October 12, 2021 to Friday, October 15, 2021 Venue: ONLINE (via ZOOM meeting), based on Japan Standard Time 9am--5pm Contact: Masaru Kada (Osaka Prefecture University) / kada@mi.s.osakafu-u.ac.jp Workshop Overview: This online workshop, hosted by RIMS (Research Institute for Mathematical Sciences, Kyoto University), is mainly (but not only) focused on recent developments in set theory of the reals. The program will contain a minicourse (a series of lectures) as well as contributed talks. In the minicourse, we invite Joerg Brendle (Kobe University) and Diego Mejia (Shizuoka University), who will give us lectures on some forcing techniques (e.g., Boolean ultrapowers, submodel methods, etc.) and related results in set theory of the reals. We welcome every researcher in set theory or related research fields. Please join us! Registration: Please submit a registration form to register your participation / contributed talk, from the following URL: https://forms.gle/1156YFMp1bN9GEDJ9 Deadline for contributed talks: September 9, 2021 Deadline for participation: October 10, 2021

## First math logic seminar of the new semester

Carnegie Mellon Logic Seminar
TUESDAY, August 31 2021 Mathematical logic seminar: 3:30 P.M., Online, Felix Weilacher, Carnegie Mellon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Borel Edge Colorings for Finite Dimensional Groups ABSTRACT: In Borel graph combinatorics, one often produces a structure (e.g. a coloring) by dividing a graph into subgraphs with finite connected components, then defining the structure on those components via some straightforward uniformization result. We first give an overview of some recent work formalizing these notions and applying them to various problems. We then present our own application to the problem of edge coloring. For Borel actions of certain groups, we find "degree plus one" Borel edge colorings, matching the classical bound of Vizing. Furthermore, for finitely generated abelian groups, we are able to exactly determine Borel edge chromatic numbers.

## Logic Seminar at NUS on Wed 18 Aug 2021 at 16:00 hrs

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 18 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Yu Liang, Nanjing University Title: Generalizing Besicovitch-Davis theorem URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Besicovitch-Davis theorem says that the Hausdorff dimension of every analytic set can be approximated by its closed subset. But the Besicovitch-Davis theorem fails for co-analytic sets under the assumption V=L as observed by Slaman. We prove that the theorem holds for arbitrary sets under ZF+sTD. We also prove that the theorem holds for Sigma-1-2-sets under Martin's axiom. This is joint work with Peng Yinhe and Wu Liuzhen.

## Logic Seminar 11 Aug 2021 16:00 hrs at NUS by Frank Stephan

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 11 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Frank Stephan Title: A survey on the structures realised by positive equivalence relations URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Let a positive equivalence relation to be an r.e. equivalence relation on the set of natural numbers with infinitely many equivalence relations. Khoussainov initiated with coauthors a deep study of the following question: Given a positive equivalence relation eta, which structures from a given set of structures does this equivalence relation realise? Here realisation means that functions in the structure are recursive and relations are r.e. with the equality itself given by the equivalence relation eta. In other words, the given r.e. structure divided by eta is the structure realised by eta. Now questions studied by Khoussainov and his coworkers included questions like "What is the partial ordering on positive equivalence relations eta,rho where eta is below rho iff every structure of the given type realised by eta is also realised by rho? Besides algebraic structures and orders, it has also been studied how the learnability notions behave with respect to uniformly r.e. one-one families realised by positive equivalence relations.

## Events next Tuesday

Carnegie Mellon Logic Seminar
TUESDAY, August 10 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 6) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic. TUESDAY, August 10, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 7) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## Events next Tuesday

Carnegie Mellon Logic Seminar

## Logic seminar and set theory reading group for next week

Carnegie Mellon Logic Seminar
ORGANIZERS' NOTE: Last week, these seminars were postponed until next week due to last minute technical issues. -------------------------------------------------------------------------- TUESDAY, July 27, 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 2) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic. TUESDAY, July 27, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 3) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## An apology to all about today's seminar

Toronto Set Theory Seminar
Hello everyone,

As some of you noticed, today there was no seminar although it was announced and not cancelled. We are very sorry about this miscommunication on our end.

Also, I offer an apology to everyone for not being in the meeting to explain the situation.

Last minute yesterday, we found out that the speaker was not going to be able to assist. I was supposed to send an email cancelling the seminar today, but I didn't.

Today I got my first vaccine shot so my mind was elsewhere (along with my internet and my computer), so I was not able to warn everyone about the cancellation.

Again, we offer an apology. This speaker will be able to participate in the seminar in september. In the meanwhile, we do not have seminar next week.

I thank everyone for your comprehension.

Best regards

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk tomorrow by Gianluca Paolini at 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:Gianluca Paolini
Date and Time: Friday, July 23rd, 2021 - 1:30pm to 3:00pm
Title: Torsion-Free Abelian Groups are Borel Complete
Abstract:
We prove that the Borel space of torsion-free Abelian groups with domain is Borel complete, i.e., the isomorphism relation on this Borel space is as complicated as possible, as an isomorphism relation. This solves a long-standing open problem in descriptive set theory, which dates back to the seminal paper on Borel reducibility of Friedman and Stanley from 1989.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk Friday 23rd June by Gianluca Paolini at 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:Gianluca Paolini
Date and Time: Friday, July 23rd, 2021 - 1:30pm to 3:00pm
Title: Torsion-Free Abelian Groups are Borel Complete
Abstract:
We prove that the Borel space of torsion-free Abelian groups with domain is Borel complete, i.e., the isomorphism relation on this Borel space is as complicated as possible, as an isomorphism relation. This solves a long-standing open problem in descriptive set theory, which dates back to the seminal paper on Borel reducibility of Friedman and Stanley from 1989.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk in ONE hour by Richard Matthews

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Richard Matthews
Date and Time: Friday, July 16th, 2021 - 1:30pm to 3:00pm
Title: Large Cardinals in Weakened Axiomatic Theories
Abstract:
The Kunen Inconsistency is an important milestone in the study of axiomatic set theory, placing a hard limit on how close the target model of a non-trivial elementary embedding can be to the full universe. In particular, it shows that the existence of a Reinhardt embedding, that is a non-trivial embedding of the full universe into itself, is inconsistent. It is well-known that all proofs we currently have rely extensively on the fact that we are working with the full power of ZFC, most notably the essential use of choice.

In this talk we shall discuss the notion of a Reinhardt embedding over several weakened base theories, primarily ZFC without Power Set, Zermelo and Power Kripke Platek. We shall see how to obtain some upper bounds, lower bounds and equiconsistency results in terms of the usual ZFC large cardinal hierarchy as well as many unexpected characteristics such embeddings can have. Moreover, we shall see that, under reasonable additional assumptions, it is possible to reobtain Kunen-type inconsistency results in both ZFC without Power Set and Power Kripke Platek plus Well-Ordering.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Events next Tuesday

Carnegie Mellon Logic Seminar
TUESDAY, July 20, 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 2) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic. TUESDAY, July 20, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 3) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## Today at 1 30 pm talk by Richard Matthews (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Richard Matthews
Date and Time: Friday, July 16th, 2021 - 1:30pm to 3:00pm
Title: Large Cardinals in Weakened Axiomatic Theories
Abstract:
The Kunen Inconsistency is an important milestone in the study of axiomatic set theory, placing a hard limit on how close the target model of a non-trivial elementary embedding can be to the full universe. In particular, it shows that the existence of a Reinhardt embedding, that is a non-trivial embedding of the full universe into itself, is inconsistent. It is well-known that all proofs we currently have rely extensively on the fact that we are working with the full power of ZFC, most notably the essential use of choice.

In this talk we shall discuss the notion of a Reinhardt embedding over several weakened base theories, primarily ZFC without Power Set, Zermelo and Power Kripke Platek. We shall see how to obtain some upper bounds, lower bounds and equiconsistency results in terms of the usual ZFC large cardinal hierarchy as well as many unexpected characteristics such embeddings can have. Moreover, we shall see that, under reasonable additional assumptions, it is possible to reobtain Kunen-type inconsistency results in both ZFC without Power Set and Power Kripke Platek plus Well-Ordering.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Two events on Tuesday

Carnegie Mellon Logic Seminar
TUESDAY, July 13, 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: An introduction to strong homology ABSTRACT: We will introduce strong homology, which aims to correct the failures of Čech homology, particularly the failure of exactness. TUESDAY, July 13, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 1) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## Talk Tomorrow by Osvaldo Guzmán 1 30 pm (Totonto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance. See attached image or follow the link below.

Here the speaker information:

Speaker:  Osvaldo Guzmán González
Date and Time: Friday, July 9th, 2021 - 1:30pm to 3:00pm
Title: MAD families and strategically bounding forcings
Abstract:
The notion of strategically bounding forcings is a natural game-theoretic
strengthening of the bounding property for partial orders.  In this talk, we
will study the basic properties of strategically bounding forcings and talk
about indestructibility of MAD families. The motivation for this work is the
problem of Roitman. I will talk about results that were obtained with
Michael Hrusak, Joerg Brendle and Dilip Raghavan.
Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Series finale

Carnegie Mellon Logic Seminar
TUESDAY, July 6, 2021 Mathematical logic seminar: 3:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 7 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module). TUESDAY, July 6, 2021 Set Theory Reading Group: 4:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 8 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

## Talk this Friday (July 9th) by Osvaldo Guzmán 1 30 pm (Totonto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

TBD

Here the speaker information:

Speaker:  Osvaldo Guzmán González
Date and Time: Friday, July 9th, 2021 - 1:30pm to 3:00pm
Title: MAD families and strategically bounding forcings
Abstract:
The notion of strategically bounding forcings is a natural game-theoretic
strengthening of the bounding property for partial orders.  In this talk, we
will study the basic properties of strategically bounding forcings and talk
about indestructibility of MAD families. The motivation for this work is the
problem of Roitman. I will talk about results that were obtained with
Michael Hrusak, Joerg Brendle and Dilip Raghavan.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## James Cummings series continues

Carnegie Mellon Logic Seminar
TUESDAY, June 29, 2021 Mathematical logic seminar:  3:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 5 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module). TUESDAY, June 29, 2021 Set Theory Reading Group:  4:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 6 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

## Talk TODAY by Riley Thornton 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:   Riley Thornton
Date and Time: Friday, June 25th, 2021 - 1:30pm to 3:00pm
Title: Effectivization in Borel Combinatorics
Abstract:
In Borel combinatorics, we often want to know when a Borel graph (or equivalence relation, quasi-order, etc) admits a Borel witness to some combinatorial property, . An effectivization theorem for says that any (lightface) graph with a Borel witness to in fact has a witness. This kind of effectivization gives a strong upper bound on the projective complexity of the set of graphs where a definable witness exists and suggests that such graphs might admit a nice structural characterization. This talk will present a streamlined method for proving effectivization theorems, give a number of applications, and discuss some related dichotomy theorems.

Please visit http://www.fields.utoronto.ca/talks/Effectivization-Borel-Combinatorics for a cleaner version of the abstract.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk this Friday 25th (in less than two days) by Riley Thornton 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:   Riley Thornton
Date and Time: Friday, June 25th, 2021 - 1:30pm to 3:00pm
Title: Effectivization in Borel Combinatorics
Abstract:
In Borel combinatorics, we often want to know when a Borel graph (or equivalence relation, quasi-order, etc) admits a Borel witness to some combinatorial property, . An effectivization theorem for says that any (lightface) graph with a Borel witness to in fact has a witness. This kind of effectivization gives a strong upper bound on the projective complexity of the set of graphs where a definable witness exists and suggests that such graphs might admit a nice structural characterization. This talk will present a streamlined method for proving effectivization theorems, give a number of applications, and discuss some related dichotomy theorems.

Please visit http://www.fields.utoronto.ca/talks/Effectivization-Borel-Combinatorics for a cleaner version of the abstract.

I'll send the next reminder in the morning of the day of the talk

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk on Thursday, June 24

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, June 24 "Preserving levels of projective determinacy and regularity properties" Johannes Schürz (TU Wien) Since \mathbf{\Pi}^1_1-determinacy is a desirable property on the reals, the natural question arises as to how one can preserve it under forcing. We will show using the technique of capturing that the statement 'Every real has a sharp' is preserved under any countable support iteration of 'simply' definable forcing notions. By the famous results of L. Harrington and D. Martin this shows that \mathbf{\Pi}^1_1-determinacy is preserved under such iterations. More generally, our theorem also shows that the statement 'M_n^\sharp(x) exists for every real x \in \omega^\omega' is preserved. By the results of I. Neeman and H. Woodin this generalizes our result to higher levels of projective determinacy. Without the existence of large cardinals the technique of capturing can still be used to show preservation results for regularity properties such as the \mathbf{\Delta}^1_2- or \mathbf{\Sigma}^1_2-Baire property. This is a joint project with J. Schilhan and P. Schlicht. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## Talk tomorrow 18th by David Schrittesser (1:30 pm to 3pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:  David Schrittesser
Date and Time: Friday, June 18th, 2021 - 1:30pm to 3:00pm
Title:  A taste of nonstandard analysis and statistical decision theory
Abstract:
Statistical decision theory takes inspiration from game theory to
provide a basic framework in which one can reason about optimality (or
lack thereof) of statistical methods, such as estimators and tests.
One (very weak) property of such methods is admissibility - roughly, a
method of estimation is admissible if there is no other which does
better under all circumstances (in a sense specified by the decision
theoretical framework).

Although a weak property, admissibility is notoriously hard to
characterize. Recently we have found a characterization of admissibility
(in a large class of statistical problems) in Bayesian terms, by using
prior probability distributions which can take on infinitesimal values.

(The talk will not presuppose any knowledge on statistics or nonstandard
analysis. Joint work with D. Roy and H. Duanmu.)
Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk this Friday 18th by David Schrittesser (1:30 pm to 3pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:  David Schrittesser
Date and Time: Friday, June 18th, 2021 - 1:30pm to 3:00pm
Title:  A taste of nonstandard analysis and statistical decision theory
Abstract:
Statistical decision theory takes inspiration from game theory to
provide a basic framework in which one can reason about optimality (or
lack thereof) of statistical methods, such as estimators and tests.
One (very weak) property of such methods is admissibility - roughly, a
method of estimation is admissible if there is no other which does
better under all circumstances (in a sense specified by the decision
theoretical framework).

Although a weak property, admissibility is notoriously hard to
characterize. Recently we have found a characterization of admissibility
(in a large class of statistical problems) in Bayesian terms, by using
prior probability distributions which can take on infinitesimal values.

(The talk will not presuppose any knowledge on statistics or nonstandard
analysis. Joint work with D. Roy and H. Duanmu.)

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk and master defense Michael Zechner

Kurt Godel Research Center

## Reminder: Boise Extravaganza in Set Theory, June 17-19

Conference
This post is an update regarding BEST, which begins next Thursday, 17 June and runs through 17 June. We are looking forward to seeing you! You can find the list of speakers and talk titles below. The latest information will always be available on the website. BEST website: https://www.boisestate.edu/math/best/ Zoom ID 92626476913 (https://boisestate.zoom.us/j/92626476913) Plenary speakers David Fernández Bretón (UNAM). Hindman’s theorem as a weak version of the Axiom of Choice Victoria Gitman (CUNY). Characterizing large cardinals via abstract logics Jun Le Goh (Wisconsin). Inseparable pairs and recursion theory Lynne Yengulalp (Wake Forest). Completeness, G-deltas, and games Joseph Zielinski (North Texas). Orbit equivalence relations of some classes of non-locally compact Polish groups Additional speakers Filippo Calderoni (UIC). Rotation equivalence and cocycle superrigidity for compact actions Natasha Dobrinen (Denver). Big Ramsey degrees of universal inverse limit structures Thomas Gilton (Pittsburgh). Club stationary reflection and the special Aronszajn tree property Osvaldo Guzmán González (UNAM). MAD families and strategically bounding forcings Randall Holmes (Boise). An outline of a proof of the consistency of New Foundations Martina Iannella (Udine). The complexity of convex bi-embeddability among countable linear orders Krzysztof Kowitz (Gdańsk). Differentially compact space and Hindman space Maxwell Levine (Freiburg). Patterns of stationary reflection Renan Mezabarba (UFES). A characterization of productive cellularity Aristotelis Panagiotopoulos (Münster). Dynamical obstructions to classification by (co)homology and other TSI-group invariants Nick Ramsey (UCLA). Exact saturation in pseudo-elementary classes Panagiotis Rouvelas (Patras). Models of predicative NF Cory Switzer (KGRC). Tight eventually different families Riley Thornton (UCLA). Effectivization in Borel combinatorics Kameryn Williams (Hawaii). Coding sets into inner mantles Jenna Zomback (UIUC). Ergodic theorems along trees
View attachments

## CMU logic events during coming week

Carnegie Mellon Logic Seminar

TUESDAY, June 15, 2021

Mathematical logic seminar:  3:30 P.M., Online, James Cummings, Carnegie Mellon University

Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us]
Meeting ID: 621 951 121

TITLE: Homological algebra for logicians

ABSTRACT: This is part 3 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology.

I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

TUESDAY, June 15, 2021

Set Theory Reading Group:  4:30 P.M., Online, James Cummings, Carnegie Mellon University

Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us]
Meeting ID: 621 951 121

TITLE: Homological algebra for logicians

ABSTRACT: This is part 4 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology.

I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

THURSDAY, June 17, 2021

Ph.D. Thesis Defense:  12:00 P.M., Online, Marcos Mazari-Armida

Zoom:
https://cmu.zoom.us/j/96301869290?pwd=Qk1zS0h6ZThmUnRpbmNLNkVJSjkrQT09

TITLE OF DISSERTATION: Remarks on classification theory for abstract elementary classes with applications to abelian group theory and ring theory

EXAMINERS:
Prof. Rami Grossberg (Committee Chair)
Prof. John Baldwin, UIC
Prof. Will Boney, Texas State
Prof. James Cummings

## Barcelona Set theory Seminar

Barcelona Logic Seminar
Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Raffaella Cutolo (Università degli Studi di Napoli Federico II)
TITLE: N-Berkeley cardinals and the two futures of set theory
DATE: 9 June 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Talk tomorrow by Piotr Szewczak (1:30 pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Piotr Szewczak
Date and Time: Friday, June 4th, 2021 - 1:30pm to 3:00pm
Title: Abstract colorings, games and ultrafilters
Abstract:
During the talk we consider various kinds of Ramsey-type theorems.

Bergelson and Hindman investigated finite colorings of the complete graph [N]^2 with vertices in natural numbers, involving an algebraic structure of N. It follows from their result that for each finite coloring of [N]^2, there are finite pairwise disjoint sets F1, F2, … such that each set Fn contains an arithmetic progression of length n and all edges between vertices from different sets Fn have the same color. Colorings of graphs appear also in the context of combinatorial covering properties. Scheepers proved that a set of reals X is Menger if and only if for every finite coloring of the complete graph whose vertices are open sets in X and an open omega-cover U of X (i.e., every finite subset of X is contained in a proper subset of X from the cover), there are finite pairwise disjoint subfamilies F1, F2, … of U such that the union of these families is point-infinite cover of X and all edges between vertices from different sets Fn have the same color.

The aim of the talk is to present a theorem that captures many results in a similar spirit (including mentioned above). To this end we use topological games and some special ultrafilters in the Stone—Cech compactification of semigroups. The research was motivated by the recent result of Tsaban, who extended the celebrated Hindman Finite Sum Theorem (and its high-dimensional version due to Milliken and Taylor) to covers of Menger spaces.

Ivan Ongay Valverde
ongay@yorku.ca
York University Postdoc (he/his)

## Talk this Friday June 4th by Piotr Szewczak (1:30 pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Piotr Szewczak
Date and Time: Friday, June 4th, 2021 - 1:30pm to 3:00pm
Title:   Abstract colorings, games and ultrafilters
Abstract:
During the talk we consider various kinds of Ramsey-type theorems.

Bergelson and Hindman investigated finite colorings of the complete graph [N]^2 with vertices in natural numbers, involving an algebraic structure of N. It follows from their result that for each finite coloring of [N]^2, there are finite pairwise disjoint sets F1, F2, … such that each set Fn contains an arithmetic progression of length n and all edges between vertices from different sets Fn have the same color. Colorings of graphs appear also in the context of combinatorial covering properties. Scheepers proved that a set of reals X is Menger if and only if for every finite coloring of the complete graph whose vertices are open sets in X and an open omega-cover U of X (i.e., every finite subset of X is contained in a proper subset of X from the cover), there are finite pairwise disjoint subfamilies F1, F2, … of U such that the union of these families is point-infinite cover of X and all edges between vertices from different sets Fn have the same color.

The aim of the talk is to present a theorem that captures many results in a similar spirit (including mentioned above). To this end we use topological games and some special ultrafilters in the Stone—Cech compactification of semigroups. The research was motivated by the recent result of Tsaban, who extended the celebrated Hindman Finite Sum Theorem (and its high-dimensional version due to Milliken and Taylor) to covers of Menger spaces.

Ivan Ongay Valverde
ongay@yorku.ca
York University Postdoc (he/his)

## Barcelona Set theory Seminar

Barcelona Logic Seminar
Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Michał Tomasz Godziszewski  (University of Warsaw)
TITLE: The Multiverse, Recursive Saturation and Well-Foundedness Mirage
DATE: 2 June 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Two events on June 8

Carnegie Mellon Logic Seminar
TUESDAY, June 8, 2021 Mathematical logic seminar: 3:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Title: Homological algebra for logicians ABSTRACT: This is part 1 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module) TUESDAY, June 8, 2021 Set Theory Reading Group: 4:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Title: Homological algebra for logicians ABSTRACT: This is part 2 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module)

## Talk Tomorrow by Boban Velickovic at 1 30 (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Boban Velickovic
Date and Time: Friday, May 28th, 2021 - 1:30pm to 3:00pm
Title:   Non vanishing higher derived limits
Abstract:
In the study of strong homology Mardesic and Prasolov isolated a certain inverse system of abelian groups A indexed by functions from \omega to \omega.
They showed that if strong homology is additive on a class of spaces containing closed subsets of Euclidean spaces then the higher derived limits lim^n A must vanish for n >0.
They also proved that under the Continuum Hypothesis lim^1 A does not vanish. On the other hand Down, Simon and Vaughan showed that under PFA lim^1 A=0
The question whether lim^n A vanishes higher n has attracted considerable attention recently. First, Bergfalk shows that it was consistent lim^2 A does not vanish.
Later Bergfalk and Lambie-Hanson showed that, assuming modest large cardinal axioms, lim^n A vanishes for all n. The large cardinal assumption was later removed by Bergfalk, Hrusak and Lambie-Hanson. We complete the picture by showing that, for any n>0, it is relatively consistent with ZFC that lim^n A is non zero.

This is joint work with Alessandro Vignati.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk on Thursday, May 27

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, May 27 "Independent families and singular cardinals" Diana Carolina Montoya (KGRC) In this talk, we will discuss the concept of independent families for uncountable cardinals. First, we will mention a summary of results regarding the existence of such families in the case of an uncountable regular cardinal. In the second part, we focus on the singular case and present two results of ours. This is joint work with Omer Ben-Neria. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at! Please note: There will be no talk in the research seminar next Thursday, June 3 (Corpus Christi).

## An interesting series of talks for grad students

Toronto Set Theory Seminar
Hello everyone,

Vera Fischer is organizing a series of short talks intended for graduate students.
The idea of the talks is one short talk once a week, with the idea to
introduce some areas of set theory to the students.

Interested students should just send Vera a short email and she will add
them to the list of participants.   vera.fischer@univie.ac.at

The time is not optimal for people in the american continent time zones
(it is 9:30am CET, Fridays, May 28-June 18), but she will record the
talks for those who want to hear them at a later point. Here is
the program until the end of the semester.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk Friday May 27th (this friday) by Boban Velickovic at 1 30 (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Boban Velickovic
Date and Time: Friday, May 28th, 2021 - 1:30pm to 3:00pm
Title:   Non vanishing higher derived limits
Abstract:
In the study of strong homology Mardesic and Prasolov isolated a certain inverse system of abelian groups A indexed by functions from \omega to \omega.
They showed that if strong homology is additive on a class of spaces containing closed subsets of Euclidean spaces then the higher derived limits lim^n A must vanish for n >0.
They also proved that under the Continuum Hypothesis lim^1 A does not vanish. On the other hand Down, Simon and Vaughan showed that under PFA lim^1 A=0
The question whether lim^n A vanishes higher n has attracted considerable attention recently. First, Bergfalk shows that it was consistent lim^2 A does not vanish.
Later Bergfalk and Lambie-Hanson showed that, assuming modest large cardinal axioms, lim^n A vanishes for all n. The large cardinal assumption was later removed by Bergfalk, Hrusak and Lambie-Hanson. We complete the picture by showing that, for any n>0, it is relatively consistent with ZFC that lim^n A is non zero.

This is joint work with Alessandro Vignati.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   David Asperó (UEA, Norwich)
TITLE: Around (*)
DATE: 26 May 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   David Asperó (UEA, Norwich)
TITLE: Around (*)