The announcements are updated continuously. For a list of talks in the coming weeks, please see here.

Carnegie Mellon University Logic Seminar
Time: Tuesday, 25 February, 4:00 – 5:00pm Pittsburgh time (22:00 – 23:00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: See the seminar webpage.

Kobe Set Theory Seminar
Time: Wednesday, 26 February, 15:30 local time (07:30 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: See the seminar webpage.

Hebrew University Set Theory Seminar
Time: Wednesday, 26 February, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: tba
Title: tba
Abstract: tba
Information: This talk will be given in hybrid format. Please contact Omer Ben-Neria and Inbar Oren for the login information.

Leeds Set Theory Seminar
Time: Wednesday, 26 February, 13:00-14:00 local time (14:00-15:00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Caltech Logic Seminar
Time: Wednesday, 26 February, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Zoltán Vidnyánszky, Eötvös Loránd University
Title: Canonicity of the Shift
Abstract: The shift graph GS on the infinite subsets of the naturals has been introduced by Kechris-Solecki-Todorcevic, alongside with the graph G0. Since then, it has become an important (and essentially unique) tool to establish complexity results concerning Borel coloring problems.
In this talk, we show that much like G0, this graph is rather canonical. First, surprisingly, every acyclic Borel graph given by a function admits a Borel homomorphism to GS. Second, I will discuss that while a G0-like dichotomy in the Borel context is not possible by complexity results, considering more relaxed versions of coloring could allow for positive results in the case of GS and even general coloring problems. Joint work with Balazs Bursics and Anett Kocsis.
Information: See the seminar webpage.

New York Set Theory Seminar
Time: Friday, 28 February, 11.00 New York time (17.00 CET)
Speaker: Andreas Lietz, TU Wien
Title: Equiconsistencies involving strengthenings of PFA
Abstract: We discuss the famous open problem of determining the exact consistency strength of PFA. We present an equiconsistency between Ben Goodman’s Sigma_n-Correct Proper Forcing Axiom, which implies PFA, and supercompact for C^(n-1)-cardinals under additional mild assumptions for large enough n. Without these assumptions we can prove a dichotomy resembling Woodin’s HOD dichotomy with a model containing the mantle taking on the role of HOD.
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 28 February, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Emily Erlebach, University of Toronto
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 28 February, 14.00 New York time (20.00 CET)
Speaker: Filippo Calderoni, Rutgers University
Title: Idealistic equivalence relations remastered
Abstract: In recent work with Luca Motto Ros we prove that under analytic determinacy there exists an analytic relation that is not class-wise Borel embeddable into any orbit equivalence relation. The result builds on an unpublished result of Becker from 2001 and fits in the area of invariant descriptive set theory. I will mainly discuss our result and how it is related to a major conjecture in the field known as the ‘E1 conjecture’.
Information: Please see the seminar webpage for the login information.

We will have our next (fifteenth) STUK meeting at UCL in London on 
Thursday 20 February 2025 at 11.00-18.00 UK time (12.00-19.00 CET), organised by Sam Coskey. 

https://www.dpmms.cam.ac.uk/~dbl25/STUK/15/

The speakers are Alberto Miguel Gómez, London; Inbar Oren, Jerusalem; and Alessandro Vignati, Paris. Please contact Sam Coskey for more information. The login for this meeting will be ucl.zoom.us/my/s.coskey.

The announcements are updated continuously. For a list of talks in the coming weeks, please see here.

Carnegie Mellon University Logic Seminar
Time: Tuesday, 18 February, 4:00 – 5:00pm Pittsburgh time (22:00 – 23:00 CET)
Speaker: Marcin Sabok, McGill University
Title: Bowen’s Problem 32 and the conjugacy problem for systems with specification
Abstract: We show that Rufus Bowen’s Problem 32 on the classification of symbolic systems with the specification property does not admit a solution that would use concrete invariants. To this end, we construct a class of symbolic systems with the specification property and show that the conjugacy relation on this class is too complicated to admit such a classification. More generally, we gauge the complexity of the classification problem for symbolic systems with the specification property. Along the way, we also provide answers to two questions related to the classification of pointed systems with the specification property: to a question of Ding and Gu related to the complexity of the classification of pointed Cantor systems with the specification property and to a question of Bruin and Vejnar related to the complexity of the classification of pointed Hilbert cube systems with the specification property. This is joint work with Konrad Deka, Dominik Kwietniak and Bo Peng.
Information: See the seminar webpage.

Leeds Set Theory Seminar
Time: Wednesday, 19 February, 13:00-14:00 local time (14:00-15:00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Caltech Logic Seminar
Time: Wednesday, 19 February, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Felix Weilacher, UC Berkeley
Title: Locally checkable labeling problems in the Borel hierarchy
Abstract: A locally checkable labeling problem (LCL) on a group Γ asks one to find a labeling of the Cayley graph of Γ satisfying a fixed, finite set of “local” constraints. Typical examples include proper coloring and perfect matching problems. We consider the existence of solutions to LCLs in the setting of descriptive set theory. For example, given a free action of Γ on a Polish space X, we might be interested in solving a given LCL on each orbit in a continuous, Borel, measurable, etc. way.
Motivated by a result of Bernshteyn’s linking continuous combinatorics and distributed computing, we are especially interested in the difference between the Borel and continuous settings. Gao, Jackson, Krohne, and Seward showed that Free Borel actions of Zn always admit Borel 3-colorings (of the natural induced graph) but that 4 colors are needed for continuous colorings when n>1. Brandt et al. demonstrated a similar separation for Fn, the free group on n generators, when n>1.
In an attempt to understand more finely the gap between Borel and continuous combinatorics, we consider the existence of Baire class m solutions to LCLs. For all n>1 and m∈ω, we extend Brandt et al.’s result by producing an LCL on Fnwhich always admits Baire class m+1 solutions, but not necessarily Baire class msolutions. There are only countably many LCLs, so it remains interesting question to determine the smallest α<ω1 for which the Baire class α and Borel combinatorics of Fn are identical.
Information: See the seminar webpage.

Set Theory in the United Kingdom 15
Time: Thursday, 20 February, 11.00-18.00 UK time (12.00-19.00 CET)
Speakers: Alberto Miguel Gómez, London; Inbar Oren, Jerusalem; Alessandro Vignati, Paris
Information: Please contact Sam Coskey for more information. The login for this meeting will be ucl.zoom.us/my/s.coskey.

Baltic Set Theory Seminar
Time: Thursday, 20 February, 16:30 – 18:00 CET
Speaker: Grigor Sargsyan
Title: Dense ideals
Abstract: The aim of this seminar series is to present topics that are of current interest. The material is usually built from ground up making it accessible to a wider audience than just experts. Feel free to participate at any time.
The topic of this semester’s seminar is based on a joint NCN-FWF project by Monroe Eskew and Grigor Sargsyan. The aim is to study dense ideals, and Sargsyan’s part of the project involves forcing over models of determinacy. The starting point of this construction is Woodin’s theorem that, given V is a model of Θreg​+V=L(P(R)), the poset Coll(ω1​,R)∗A˙dd(1,ω2​) forces the existence of an ω1​-dense ideal on ω1​. The aim of this lecture is to present the proof of this theorem. We will start slowly and cover the background material that leads to the proof. There are two documents that contain the proof.
– Forcing a dense ideal on ω1​ over a model of determinacy by Obrad Kasum
– Ideals and Strong Axioms of Determinacy by Dominik Adolf, Grigor Sargsyan, Nam Trang, Trevor Wilson, Martin Zeman
Information: This talk will be given in hybrid format. Please contact Rahman Mohammadpour and Grigor Sargsyan for information how to participate.

Toronto Set Theory Seminar
Time: Friday, 21 February, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Jing Zhang, University of Toronto
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 21 February, 14.00 New York time (20.00 CET)
Speaker: Alf Dolich, CUNY
Title: Expansions of ordered Abelian groups of low rank
Abstract: Expansions of the ordered additive group of the reals (or more generally definably complete expansions of ordered Abelian groups) of finite dp-rank are a class of reasonably well-behaved ordered structures that generalize the class of o-minimal structures. In this talk I will give a survey of ongoing work with John Goodrick on exploring the properties of definable sets in this class of structures. 
Information: Please see the seminar webpage for the login information.

The announcements are updated continuously. For a list of talks in the coming weeks, please see here.

Hebrew University Set Theory Seminar
Time: Wednesday, 5 February, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Yair Hayut
Title: Tukey types of ultrafilters on omega
Abstract: Using iteration of Mathias-like forcings, Kunen showed that consistently there is an ultrafilter on omega with generating set of order type an uncountable regular cardinal , even when the continuum is much larger than .
As the cofinal types of an ultrafilter (the Tukey-type) is not necessarily a cardinal, it is natural to ask which cofinal types of directed partial orders can indeed be the Tukey type of ultrafilters on omega (or generally, kappa-closed ultrafilters on kappa).
In this talk, I will present a joint work with Tom Benhamou, James Cummings, Gabe Goldberg and Alejandro Poveda, in which we show the consistency of the existence of an ultrafilter on  in which there is a cofinal set (mod bounded error) of order type  (the product order). I will discuss some of the limitations of the method.  
Information: This talk will be given in hybrid format. Please contact Omer Ben-Neria and Inbar Oren for the login information.

Leeds Set Theory Seminar
Time: Wednesday, 5 February, 13:00-14:00 local time (14:00-15:00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Caltech Logic Seminar
Time: Wednesday, 5 February, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: William Chan, Vienna University of Technology
Title: Sigma Scattered Linear Orderings
Abstract: In this talk, we will discuss properties of sigma scattered linear orderings in the descriptive set theoretic world.
Information: See the seminar webpage.

Baltic Set Theory Seminar
Time: Thursday, 6 February, 16:30 – 18:00 CET
Speaker: Grigor Sargsyan
Title: Dense ideals
Abstract: The aim of this seminar series is to present topics that are of current interest. The material is usually built from ground up making it accessible to a wider audience than just experts. Feel free to participate at any time.
The topic of this semester’s seminar is based on a joint NCN-FWF project by Monroe Eskew and Grigor Sargsyan. The aim is to study dense ideals, and Sargsyan’s part of the project involves forcing over models of determinacy. The starting point of this construction is Woodin’s theorem that, given V is a model of Θreg​+V=L(P(R)), the poset Coll(ω1​,R)∗A˙dd(1,ω2​) forces the existence of an ω1​-dense ideal on ω1​. The aim of this lecture is to present the proof of this theorem. We will start slowly and cover the background material that leads to the proof. There are two documents that contain the proof.
– Forcing a dense ideal on ω1​ over a model of determinacy by Obrad Kasum
– Ideals and Strong Axioms of Determinacy by Dominik Adolf, Grigor Sargsyan, Nam Trang, Trevor Wilson, Martin Zeman
Information: This talk will be given in hybrid format. Please contact Rahman Mohammadpour and Grigor Sargsyan for information how to participate.

Cross-Alps Logic Seminar
Time: Friday, 7 February, 16.00-17.00 CEST
Speaker: S. Iyer, Carnegie Mellon University
Title: tba
Abstract: tba
Information: The event will stream on the Webex platform. Please write to  luca.mottoros [at] unito.it  for the link to the event.

New York Set Theory Seminar
Time: Friday, 7 February, 11.00 New York time (17.00 CET)
Speaker: Ali Enayat, University of Gothenburg
Title: Models of set theory: extensions and dead-ends
Abstract: This is a two-part talk concerning existence/non-existence of certain kinds of extensions of arbitrary models of ZF, with no regard to countability or well-foundedness of the models involved. The talk is based a recent preprint: arXiv:2406.14790v1. The results presented include the following two. In Theorem A below, N is said to be a conservative elementary extension of M if N is an elementary extension of M with the property that the intersection of every parametrically definable subset of N with M is parametrically definable in M.
Theorem A. Every model M of ZF with a definable global well-ordering has a conservative elementary extension N that contains an ordinal above all of the ordinals of M.
Theorem B. Every consistent extension of ZF has a model of power aleph_1 that has no end extension to a model of ZF.
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 7 February, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Jorge Antonio Cruz Chapital
Title: Uniform convergence topology on separable subsets
Abstract: For a topological space X, let (RX)s := (RX,Ts) be the cartesian product of |X| copies of the real line R with the topology of the uniform convergence on separable subsets of X. In this talk we will analyze the subspace C(X) of (RX)s of all real-valued continuous functions on X, denoted by Cs(X). 
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 7 February, 14.00 New York time (20.00 CET)
Speaker: Assaf Shani, Concordia University
Title: Generic dichotomies for Borel homomorphisms for the finite Friedman-Stanley jumps
Abstract: The talk will begin by discussing the basic definitions and general goals behind the theory of Borel equivalence relations. We focus on the Friedman-Stanley jumps =+n, for n=1,2,… and n=ω. These Borel equivalence relations represent the notions of being classifiable using invariants which are countable sets of reals, countable sets of countable sets of reals, and so on. We consider the problem of constructing a Borel reduction from =+n to some other equivalence relation. 
For n=1 the situation is well understood and there are many such results. For example: Marker proved that for a first order theory with an uncountable type space, its isomorphism relation is above =+1; Larson and Zapletal characterized the analytic equivalence relations above =+1 as those which are ‘unpinned’ in the Solovay extension. 
In this talk we present a new technique for proving that an equivalence relation is above =+n, when n>1, based on Baire-category methods. As corollaries, we conclude that =+ω is ‘regular’ (answering a question of Clemens), and that =+n is ‘in the spectrum of the meager ideal’ (extending a result of Kanovei, Sabok, and Zapletal for n=1).
Information: Please see the seminar webpage for the login information.

The Roaming Logic Conference will take place at the University of Warsaw on 9 – 11 May, 2025.

The Mostowski Lecture will be presented by Su Gao (Nankai University)

Invited speakers:

David Aspero, Joan Bagaria, Adam Bartoš, Dana Bartošová, Mikołaj Bojańczyk, Riccardo Camerlo, Aleksander Cieślak, Natasha Dobrinen, Ali Enayat, Kentaro Fujimoto, Damian Głodkowski, Adam Kwela, Michael Pinsker, Tomasz Rzepecki, Grigor Sargsyan and Piotr Szewczak.

Scientific committee:

Piotr Borodulin-Nadzieja (University of Wrocław), Cezary Cieśliński (University of Warsaw), Rafał Filipów (University of Gdańsk), Szymon Głąb (Łódź University of Technology), Maciej Malicki (University of Warsaw), Szymon Toruńczyk (University of Warsaw)

Local organisers:

Maciej Malicki (University of Warsaw), Julia Ścisłowska (University of Warsaw)

• The registration deadline for accommodation applicants is March 15th.

• The deadline for registration is April 15th.

Some funding for students is available. Interested students can contact the local organisers.

More information can be found on the conference website.

The announcements are updated continuously. For a list of talks in the coming weeks, please see here.

Hebrew University Set Theory Seminar
Time: Wednesday, 29 January, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: tba
Title: tba
Abstract: tba
Information: This talk will be given in hybrid format. Please contact Omer Ben-Neria and Inbar Oren for the login information.

Leeds Set Theory Seminar
Time: Wednesday, 29 January, 13:00-14:00 local time (14:00-15:00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Caltech Logic Seminar
Time: Wednesday, 29 January, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Bo Peng, McGill University
Title: Bowen’s Problem 32 and the conjugacy problem for systems with specification
Abstract: We show that Rufus Bowen’s Problem 32 on the classification of symbolic systems with the specification property does not admit a solution that would use concrete invariants. To this end, we construct a class of symbolic systems with the specification property and show that the conjugacy relation on this class is too complicated to admit such a classification. More generally, we gauge the complexity of the classification problem for symbolic systems with the specification property. Along the way, we also provide answers to two questions related to the classification of pointed systems with the specification property: to a question of Ding and Gu related to the complexity of the classification of pointed Cantor systems with the specification property and to a question of Bruin and Vejnar related to the complexity of the classification of pointed Hilbert cube systems with the specification property. This is joint work with Konrad Deka, Dominik Kwietniak and Marcin Sabok.
Information: See the seminar webpage.

Baltic Set Theory Seminar
Time: Thursday, 30 January, 16:30 – 18:00 CET
Speaker: Grigor Sargsyan
Title: Dense ideals
Abstract: The aim of this seminar series is to present topics that are of current interest. The material is usually built from ground up making it accessible to a wider audience than just experts. Feel free to participate at any time.
The topic of this semester’s seminar is based on a joint NCN-FWF project by Monroe Eskew and Grigor Sargsyan. The aim is to study dense ideals, and Sargsyan’s part of the project involves forcing over models of determinacy. The starting point of this construction is Woodin’s theorem that, given V is a model of Θreg​+V=L(P(R)), the poset Coll(ω1​,R)∗A˙dd(1,ω2​) forces the existence of an ω1​-dense ideal on ω1​. The aim of this lecture is to present the proof of this theorem. We will start slowly and cover the background material that leads to the proof. There are two documents that contain the proof.
– Forcing a dense ideal on ω1​ over a model of determinacy by Obrad Kasum
– Ideals and Strong Axioms of Determinacy by Dominik Adolf, Grigor Sargsyan, Nam Trang, Trevor Wilson, Martin Zeman
Information: This talk will be given in hybrid format. Please contact Rahman Mohammadpour and Grigor Sargsyan for information how to participate.

Toronto Set Theory Seminar
Time: Friday, 31 January, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Juris Steprans
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.