The conference in honor of Jörg Brendle, on the occasion of his 60th birthday, will be held entirely in person from September 2nd to 5th, 2025, at Kobe University.

We will have invited talks from close colleagues, collaborators, students, and even students’ students, of Professor Brendle.

See the website for detailed information.

https://sites.google.com/view/brendle60/

The conference will be succeeded by The 18th ALC (Asian Logic Conference) in Kyoto (September 8 to 12).

https://www2.kobe-u.ac.jp/~brendle/alc2025/main.html

We recommend booking hotels in advance, especially if you plan to attend the ALC, because of the recent influx of foreign tourists in Kyoto. Hotels and travel information are available on both websites.

Student travel support (for both conferences) for students with an ASL (Association of Symbolic Logic) membership is available. Check both websites for details on how to apply (deadline: June 1st, 2025).

Registration is open (free)! Although registration is not mandatory, we encourage participants (including speakers) to register in order to have an idea of the number of participants. However, registration is mandatory for attending the Conference Party.

This Conference is sponsored by the JSPS KAKENHI Grant Numbers JP23K03198 (Diego Mejía) and JP25K07099 (Teruyuki Yorioka), and by the Association of Symbolic Logic.

Please contact Diego A. Mejía (damejiag “at” people “dot” kobe-u “dot” ac “dot” jp) or Teruyuki Yorioka (yorioka “at” shizuoka “dot” ac “dot” jp) for inquiries.

See you in Kobe!

The organizers

Diego A. Mejía (Kobe University)

Hiroaki Minami (Aichi Gakuin University)

Hiroshi Sakai (University of Tokyo)

Teruyuki Yorioka (Shizuoka University)

The Cluster of Excellence Mathematics Münster supports outstanding 
international master’s students in all fields of mathematics including mathematical logic.

Until *May 30, 2025*, international students who are interested in 
completing their Master’s studies in Münster have the opportunity to 
apply for a *full grant scholarship*.

Please find more details on the following poster.

We are pleased to announce that the 8th Workshop on Generalized Descriptive Set Theory will take place on 20–22 August 2025 at the University of Helsinki, Finland.

The 8th Workshop on Generalized Descriptive Set Theory continues a series that began in 2014. Since its first edition, the Workshop on Generalized Descriptive Set Theory has been a key venue for advancing research in the field featuring renowned speakers and fostering discussion and collaboration.

The 8th edition will cover topics such as model-theoretic applications, cardinal characteristics, higher descriptive set theory, topology, and Borel reducibility in GBS, among others.

The workshop features the participation of the following speakers:
– Vera Fischer, University of Vienna
– Tapani Hyttinen, University of Helsinki
– Philipp Lücke, University of Hamburg
– Luca Motto Ros, University of Turin
– Philipp Schlicht, University of Siena
– Boban Velickovic, Paris Diderot University (TBC)

The workshop features contributed talks that last 30 minutes. If you wish to deliver a contributed talk, please send the title and abstract to the e-mail miguel.moreno ‘at’ helsinki.fi no later than May 30, 2025.

The registration for the workshop opens on June 16, 2025. It has a registration fee of 50 euros.

It is organized by the University of Helsinki.
Organizing committee:
– Miguel Moreno, University of Helsinki
– Jouko Väänänen, University of Helsinki

More information about the workshop can be found on the website of the workshop: https://www.helsinki.fi/en/conferences/8th-workshop-generalized-descriptive-set-theory

If you have any questions or need more information concerning the conference, please do not hesitate to contact us at: miguel.moreno ‘at’ helsinki.fi

Please feel free to forward this information to anyone, who may be interested.
Looking forward to seeing you in Helsinki.

Kind regards,
Miguel Moreno and Jouko Väänänen

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

Hebrew University Set Theory Seminar
Time: Wednesday, 16 April, 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, 16 April, 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, 16 April, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Tyler Arant, UCLA
Title: Graphings of Arithmetical Equivalence Relations
Abstract: A graphing of an equivalence relation E is a graph G whose connectivity equivalence relation is equal to E. In previous joint work with Alekos Kechris and Patrick Lutz, we studied analytic equivalence relations which have Borel graphings. In this talk, we will discuss new results about when arithmetical equivalence relations have definable graphings which are lower down in the arithmetical hierarchy. In particular, we will see that for any computable relational language L, computable isomorphism of L-structures presented on the natural numbers (a Σ03equivalence relation) has a Π02 graphing. We will also prove a result on how to arithmetically construct a graphing of the Friedman-Stanley jump of E from a graphing of E.
Information: See the seminar webpage.

Baltic Set Theory Seminar
Time: Thursday, 17 April, 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, 18 April, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: tba
Title: tba
Abstract: tba
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, 2 April, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Matan Ben-Asher
Title: Arrow Partition and Measurable Cardinals (continued)
Abstract: In 1985, Larson and Baumgartner built a negative partition relation using a Diamond Sequence. Later, in 1990, Larson proved a positive relation using Martin’s Axiom. In my talks, I will introduce the arrow notation and present one of Larson’s proofs. I will then discuss new results concerning measurable cardinals.This research is part of my master’s thesis, supervised by Y. Hayut and S. Garti.
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, 2 April, 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.

Vienna Research Seminar in Set Theory
Time: Thursday, 3 April, 11:30-13:00 CET
Speaker: A. Lihuen Fatalini, Universität Münster
Title: Amalgamation, Axiom of Choice and Euclidean geometry II
Abstract: This is a 2 talk series (this is part 2).
We will show that there is a model of ZF with no well order on the reals in which there is a partition of R3 in unit circles. The major obstacle is satisfying some amalgamation, for which geometrical and algebraic considerations are needed. If the time allows, we will see how these techniques can generalize to other applications.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 3 April, 15:00 – 15:50 CET
Speaker: A. Lihuen Fatalini, Universität Münster
Title: Paradoxical sets and the Axiom of Choice
Abstract: There are many “paradoxical sets” of reals that can be obtained using a well-ordering of the reals, which is a consequence of the Axiom of Choice. In ZF, can we recover the well-ordering of the reals from the existence of a given paradoxical set? Under certain conditions of Extendability and Amalgamation, we give a negative answer to this question. In particular, we solve it for the paradoxical set given by a partition of R3 in unit circles. For this, some geometrical and algebraic considerations are needed.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 3 April, 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, 4 April, 16.00-17.00 CEST
Speaker: H. Herbelin, INRIA
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, 4 April, 11.00 New York time (17.00 CET)
Speaker: Siiri Kivimäki, University of Helsinki
Title: Partitions and trees in Ehrenfeucht-Fraïssé games
Abstract: We are interested in when are two uncountable models ‘similar’ – elementarily equivalent, elementarily equivalent in a stronger logic, or even isomorphic. Such equivalence is always characterized in terms of an Ehrenfeucht-Fraïssé game. We give two modifications of the standard Ehrenfeucht-Fraïssé game and discuss the logics these give rise to. The modified versions involve partitions of models and making the game longer using an Aronszajn tree as a game clock.
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 4 April, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Mark Poor, Cornell University
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 4 April, 14.00 New York time (20.00 CET)
Speaker: Valentina Harizanov, George Washington University
Title: Computable structures and their effective products
Abstract: We consider a computability-theoretic version of the ultraproduct construction for an infinite uniformly computable sequence of structures, where the role of an ultrafilter is played by an infinite set of natural numbers that cannot be split into two infinite subsets by any computably enumerable set. For computable structures, effective powers preserve only the first-order sentences of lower levels of quantifier complexity. Additional decidability of the structure increases preservation of the fragments of its theory in an effective power, so that a structure with a computable elementary diagram is elementarily equivalent to its effective power. We will present a number of recent collaborative results.
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, 26 March, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Matan Ben-Asher 
Title: Arrow partition and measurable cardinals
Abstract: In 1985, Larson and Baumgartner built a negative partition relation using a Diamond Sequence. Later, in 1990, Larson proved a positive relation using Martin’s Axiom. In my talks, I will introduce the arrow notation and present one of Larson’s proofs. I will then discuss new results concerning measurable cardinals.This research is part of my master’s thesis, supervised by Y. Hayut and S. Garti.
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 March, (unusual time) 15:00-16:00 local time (16:00-17:00 CET)
Speaker: Garrett Ervin, Caltech
Title: Cancellation and absorption in lexicographic products
Abstract: Morel proved that a linear order $X$ can be cancelled on the right in lexicographic products if and only if $X$ is not left-absorbing. That is, the right cancellation law $AX \cong BX \Rightarrow A \cong B$ holds for all linear orders $A$ and $B$ if and only if there is no non-singleton order $L$ such that $LX \cong X$.
In joint work with Eric Paul, we examined the extent to which Morel’s theorem holds on the left. We were able to prove that if $X$ is a linear order that is not right-absorbing, then the left cancellation law $XA \cong XB \Rightarrow A \cong B$ holds for all orders $A$ and $B$ that are not left-absorbing. Moreover, we showed this is the best possible left cancellation law for the class of non-right-absorbing orders, and in particular that the naive left-sided version of Morel’s theorem is false. In this talk, I will discuss these results and outline a possible approach for adapting them to get a characterization of the globally left-cancelling linear orders. 
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Vienna Research Seminar in Set Theory
Time: Thursday, 27 March, 11:30-13:00 CET
Speaker: A. Lihuen Fatalini
Title: Amalgamation, Axiom of Choice and Euclidean geometry I
Abstract: This is part 1 of a 2 talk series.
We will show that there is a model of ZF with no well order on the reals in which there is a partition of R3 in unit circles. The major obstacle is satisfying some amalgamation, for which geometrical and algebraic considerations are needed. If the time allows, we will see how these techniques can generalize to other applications.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 27 March, 15:00 – 15:50 CET
Speaker: P. Eleftheriou, University of Leeds
Title: On the global linear Zarankiewicz problem
Abstract: The global Zarankiewicz’s problem for hypergraphs asks for an upper bound on the number of edges of a hypergraph, whose edge relation is induced by a fixed hypergraph E that has no sub-hypergraphs of a given size. Basit-Chernikov-Starchenko-Tao-Tran (2021) obtained linear Zarankiewicz bounds in the case of a semilinear E, namely E definable ina linear o-minimal structure. Moreover, those bounds characterised linearity among all o-minimal structures.
In this talk, we extend this theorem to a broad range of “linear-like” structures, in o-minimal, Presburger Arithmetic and stability theoretic settings. Among others, we characterise combinatorially those o-minimal structures that do not expand a real closed field.
Joint work with Aris Papadopoulos.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 27 March, 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.

New York Set Theory Seminar
Time: Friday, 28 March, 11.00 New York time (17.00 CET)
Speaker: Stefan Hoffelner, TU Wien
Title: The global Σ1n+2-Uniformization Property and BPFA
Abstract: We show that, given a reflecting cardinal, one can generically produce a universe of BPFA in which additionally the Σ1n+2-uniformization property holds for every n simultaneously.
Information: Please see the seminar webpage for the login information.

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

New York Logic Workshop
Time: Friday, 28 March, 14.00 New York time (20.00 CET)
Speaker: Aaron Anderson, University of Pennsylvania
Title: Examples of Distal Metric Structures
Abstract: We identify several examples of distal metric structures and examine several consequences of distality, such as the existence of distal cell decompositions, in each. These results include joint work with Itaï Ben Yaacov and with Diego Bejarano. One class of examples starts with finding a metric structure whose automorphism group is the group of increasing homeomorphisms of the unit interval. We will discuss some properties of this structure and extrapolate to other models of its theory, which we call ‘dual linear continua.’ Another source of examples includes real closed metric valued fields. These give rise to a notion of ordered metric structure, providing a viewpoint to study o-minimality in continuous logic.
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, 19 March, 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, 19 March, 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.

Vienna Research Seminar in Set Theory
Time: Thursday, 20 March, 11:30-13:00 CET
Speaker: J. Schilhan, Universität Wien
Title: The theory of symmetric systems and extensions III
Abstract: In this 3 talk series (part 1, part 2, part 3: this part) I will give an introduction to the technique of symmetric systems and present some of the recent results we have obtained joint with A. Karagila. Symmetric systems produce so called symmetric extensions which are intermediate models between V and forcing extension V[G]. These models may not satisfy the Axiom of Choice and their primary use is to obtain consistency results for ZF. On the other hand, they are also useful in generally understanding and classifying intermediate models.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 20 March, 15:00 – 15:50 CET
Speaker: T. van der Vlugt, TU Wien
Title: Meagre and Null Ideals for Uncountable Cardinals
Abstract: We will consider the space of functions from λ to κ for various choices of λ and κ. In the first part of the talk we define topologies on such spaces and discuss the μ-meagre ideal (i.e. sets that are unions of μ-many nowhere dense sets) and their associated cardinal invariants. In the second part, we will look at various ways to look at (cardinal invariants of) the null ideal on such spaces.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 20 March, 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.

New York Logic Workshop
Time: Friday, 21 March, 14.00 New York time (20.00 CET)
Speaker: Sheila Miller Edwards, Arizona State University
Title: How to construct a free, two-generated left distributive algebra of elementary embeddings
Abstract: The relationship between left distributivity and very large cardinal embeddings was discovered in the 1980s but remains, in many ways, mysterious. In the late 1980s Richard Laver showed that the closure of a single elementary embedding under the application operation generates a free left distributive algebra and demonstrated the linearity of a particular ordering on terms of the free left distributive algebra (given the existence of such embeddings). Patrick Dehornoy later used the braid group on infinitely many generators to show the linearity of that ordering relation within ZFC. (The consistency strength of other related theorems is still unknown). David Larue subsequently extended that work to demonstrate braid group representations of the free left distributive algebra on n generators, for any natural number n. Still elusive was an algebra of embeddings isomorphic to a free left distributive algebra on more than one generator. We present an inverse limit construction of such a free, two-generated left distributive algebra of embeddings from a slightly stronger large cardinal assumption than the one used by Laver. (Joint work with Andrew Brooke-Taylor and Scott Cramer.)
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.

Leeds Set Theory Seminar
Time: Wednesday, 12 March, 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.

Vienna Research Seminar in Set Theory
Time: Thursday, 13 March, 11:30-13:00 CET
 J. Schilhan, Universität Wien
Title: The theory of symmetric systems and extensions II
Abstract: In this 3 talk series I will give an introduction to the technique of symmetric systems and present some of the recent results we have obtained joint with A. Karagila. Symmetric systems produce so called symmetric extensions which are intermediate models between V and forcing extension V[G]. These models may not satisfy the Axiom of Choice and their primary use is to obtain consistency results for ZF. On the other hand, they are also useful in generally understanding and classifying intermediate models.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 13 March, 15:00 – 15:50 CET
Speaker: Martina Iannella, Technische Universität Wien
Title: Classification of 3-manifolds
Abstract: A classification problem consists of a set of mathematical objects equipped with some natural equivalence relation; a solution to such a problem is an assignment of complete invariants.
In this talk we consider the problem of classifying 3-manifolds up to homeomorphism from the perspective of descriptive set theory. We briefly discuss the framework of Borel reducibility, a standard tool for comparing the complexity of different classification problems, and present our recent result which determines the exact complexity of the classification of non-compact 3-manifolds up to homeomorphism.
This is joint work in progress with Vadim Weinstein (Oulu).
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 13 March, 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.

New York Logic Workshop
Time: Friday, 14 March, 14.00 New York time (20.00 CET)
Speaker: Alex Kruckman, Wesleyan University
Title: Some pseudofinite rings and modules
Abstract: Recall that a structure is pseudofinite if every sentence satisfied by that structure has a finite model – equivalently, if the structure is elementarily equivalent to an ultraproduct of finite structures. In this talk, I will present some work in progress from two independent projects around pseudofinite rings and pseudofinite modules: one is joint work with Alex Van Abel, the other is work of my PhD student Roberto Torres. These two projects are linked by the important role played by the class of von Neumann regular rings.
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 March, 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, 5 March, 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 March, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Garrett Ervin, Caltech
Title: A dichotomy theorem for order types of orbit equivalence relations on R
Abstract: We introduce a natural notion of order-isomorphism between equivalence relations on R and prove the following dichotomy theorem: if E=EG is the orbit equivalence relation of a group G of orientation-preserving homeomorphisms of Rall of whose orbits are dense in R, then either E is isomorphic to the orbit equivalence relation of a group of translations, or E embeds an isomorphic copy of the tail-equivalence relation.
We also discuss connections between this theorem and several related dichotomy theorems about linear orders due to Lindenbaum, Jullien, and Holland. In each of these theorems, the dichotomy in question distinguishes between linear orders that can in some sense be split into two copies of themselves and linear orders for which there is no such splitting.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 6 March, 11:30-13:00 CET
Speaker: J. Schilhan, Universität Wien
Title: The theory of symmetric systems and extensions I
Abstract: In this 3 talk series I will give an introduction to the technique of symmetric systems and present some of the recent results we have obtained joint with A. Karagila. Symmetric systems produce so called symmetric extensions which are intermediate models between V and forcing extension V[G]. These models may not satisfy the Axiom of Choice and their primary use is to obtain consistency results for ZF. On the other hand, they are also useful in generally understanding and classifying intermediate models.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 6 March, 15:00 – 15:50 CET
Speaker: S. Eterović, Universität Wien
Title: Likely Intersections
Abstract: Many important problems in arithmetic geometry focus on the interplay between local arithmetic behavior and global geometric behavior. A way of making this precise is by studying so-called unlikely intersections, which are presumably governed by the (very open) Zilber-Pink conjecture.
In this talk I will introduce the Zilber-Pink conjecture, discuss some cases that are known, and present joint work with Thomas Scanlon where we prove a strong counterpart of Zilber-Pink describing the presence of likely intersections.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 6 March, 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 March, 16.00-17.00 CEST
Speaker: S. Iyer, Carnegie Mellon University
Title: Extremely amenable groups of homeomorphisms
Abstract: A topological group is extremely amenable if every continuous action of it on a compact Hausdorff space has a fixed point. We will first survey some known results/ general tools about extreme amenability for homeomorphism groups of connected compact metric spaces. We outline a construction due to Uspenskij which gives a condition equivalent to extreme amenability for this setting. We then show a Ramsey-type statement for subsets of simplices that, together with Uspenskij’s construction, gives a new proof of a theorem due to Pestov: that the group of orientation-preserving homeomorphisms of the closed unit interval is extremely amenable. This is joint work with Lukas Michel and Alex Scott.
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 March, 11.00 New York time (17.00 CET)
Speaker: Tom Benhamou, Rutgers University
Title: Ultrafilters on measurables and non-measurables: discrepancies and techniques
Abstract: We present new results regarding the depth and Tukey spectrum of general ultrafilters and simple
Pλ-points at a measurable cardinal. In particular we prove that on a measurable cardinal there can only be a single λ for which there exists a simple Pλ-point – this is in sharp contrast to ω. Finally we will present several models in which we analyze the depth and Tukey spectrum of an ultrafilter, and their effect on generalized cardinal characteristics.
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 7 March, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Narmada Varadarajan, University of Toronto
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 7 March, 14.00 New York time (20.00 CET)
Speaker: Maya Saran, Mathematics Foundation of America
Title: A descriptive-set-theoretic result on sigma-ideals of compact sets
Abstract: Polish spaces, the objects of study of descriptive set theory, are completely metrizable topological spaces that have a countable dense subset. For example, the reals – the first Polish space in the world. We will look at ‘sigma-ideals’ of compact subsets of a Polish space. Think of a sigma-ideal as being a collection of ‘small’ compact sets, under some notion of smallness — so for example, your Polish space could be the interval [0,1] and your sigma-ideal could be the collection of all its compact sets of Lebesgue measure 0. The descriptive-set-theoretic study of these objects yields rich results for the following reason. If you look at the collection of all the compact subsets of a Polish space, that too, topologized and metrized in a natural way, turns out to be a Polish space. This means that you can look at your sigma-ideal of compact sets in two places: in the original space, say E, and in the `hyperspace’ of all compact sets of E. In this talk we will deal with sigma-ideals that can be represented in a very nice way inside this hyperspace, and we will examine the behaviour of so-called G-delta subsets of E with respect to this representation.
Information: Please see the seminar webpage for the login information.