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

Hebrew University Set Theory Seminar
Time: Wednesday, 4 June, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Yair Hayut
Title: Dense ideals
Abstract: In this series of talks, I will present joint work with Monroe Eskew. The main result of our work is the relative consistency of the existence of dense ideals on all successors of regular cardinals simultaneously: namely, it is consistent that there is a -dense normal ideal on  for every cardinal  which is a successor of a regular cardinal. In particular, we show that it is consistent that for every <img height="9" width="41" src="https://ci3.googleusercontent.com/meips/ADKq_NZOHZq-dV0JH17ip8eCCwmfxEM_HnT0zFnUp4Xbm74bQpXHpKQBsCLQJXujWvfLktgbUZ4lxZwAyC32xdJdzqvc8bqig9xChtBgJLXbWANfP4jV4oPrCp1ciJvcGtr3Pj7BrA=s0-d-e1-ft#https://s0.wp.com/latex.php?zoom=3&bg=ffffff&fg=000000&s=0&latex=n%3C%5Comega&quot; alt="n, there exists an -dense ideal on , thus extending Foreman’s result for .
Beginning in the 1980s, Foreman proposed the philosophy of generic large cardinal axioms — a parallel hierarchy to the traditional large cardinal axioms. Unlike the classical axioms, these generic versions aim to settle set-theoretic questions about small cardinals, such as the Continuum Hypothesis. Just as large cardinals are characterized via combinatorial objects like measures, generic large cardinal axioms correspond to the existence of ideals with certain properties. One way to measure the strength of such an axiom is by how small the Boolean algebra of positive sets mod the ideal can be: the smaller, the better.
We begin by presenting a variant of Laver’s consistency proof for the existence of a saturated ideal. If time permits, we will also show that Martin’s Maximum implies the saturation of the non-stationary ideal on .
Later in the series, we will describe the classical construction of a dense ideal on  from an almost-huge cardinal. The main part of our work involves a new forcing notion — a variant of a construction introduced by Shioya. We iterate this forcing and, starting from a huge cardinal, produce a dense ideal on the successor of any regular cardinal.
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, 4 June, 13:00-14:00 local time (14:00-15:00 CEST)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Caltech Logic Seminar
Time: Wednesday, 4 June, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CEST)  
Speaker: Hyung Mook Kang, University of North Texas
Title: Continuous Hyperfiniteness
Abstract: It has been a long-lasting problem, posed by Weiss (1984), whether any Borel action of a countable amenable group on a standard Borel space gives rise to a hyperfinite Borel equivalence relation. This can be equivalently reformuated as whether countable amenable group action in a Borel way gives rise to the orbit equivalence relation being hyperfinite, liminf of a sequence of finite Borel equivalence relations, Borel embeddable into E0 or Borel reducible to E0. It is possible to consider these questions in a continuous setting, with the action being continuous, and a space being zero dimensional second countable Hausdorff, to see whether the induced orbit equivalence relation is continuously hyperfinite, liminf of G-clopen finite equivalence relations, continuously embeddable to E0 or continuously reducible to E0. We discuss that the one implies the other, but not necessarily the other way around. Also, we discuss the continuous analogue of the Borel asymptotic dimension, discuss its continuous embeddability and show that the shift action of Gto 2G should have infinite continuous asymptotic dimension when G has an element of infinite order. Finally, we discuss the continuous embedding of a locally finite group into E0.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 5 June, 11:30-13:00 CEST
Speaker: Jindra Zapletal, University of Florida, Gainesville
Title: Axiomatizing balanced forcing
Abstract: Almost 10 years ago, with Paul Larson we developed the method of balanced forcing for consistency results in ZF+DC In this talk, I will provide a novel axiomatization of the method, which is much less technical and more general. The parallels with geometric model theory become readily apparent.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 5 June, 15:00 – 15:50 CEST
Speaker: Jindra Zapletal, University of Florida, Gainesville
Title: Cohomology of amalgamation diagrams
Abstract: I define amalgamation diagram problems for models of set theory. I show how answers to such problems can lead to independence results in set theory. For some amalgamation diagram problems, their resolution amounts to calculating cohomology groups of certain natural cochain complexes.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Cross-Alps Logic Seminar
Time: Friday, 6 June, 16.00-17.00 CEST
Speaker: B. Siskind, TU Wien
Title: The status of Martin’s Conjecture
Abstract: Martin’s Conjecture is a proposed classification of Turing-invariant functions under the Axiom of Determinacy, consisting of two parts. Part 1 of the conjecture states that every Turing-invariant function is either equivalent to a constant function or above the identity function with respect to a natural order on Turing-invariant functions, the Martin order. Part 2 of the conjecture says that the functions which are Martin-above the identity are pre-well-ordered by the Martin order, with the successor operation given by composition with the Turing jump. Both parts of the conjecture remain open, even for Borel functions. However, restricting the conjecture to the ostensibly smaller class of functions that are order-preserving for the Turing-reducibility order turns out to be more tractable. We have shown that part 1 of the conjecture holds restricted to the class of order-preserving functions and, building on work of Slaman and Steel, part 2 of the conjecture holds through the iterates of the hyperjump. Furthermore, there is a natural plan for proving order-preserving Martin’s Conjecture in models of determinacy which have been analyzed by inner model theory. This is joint work with Patrick Lutz.
Information: The event will stream on the Webex platform. Please write to  luca.mottoros [at] unito.it  for the link to the event.

The University of Udine (NE Italy) is opening for new PhD positions in Mathematical and Physical Sciences:

Mathematical Logic in Udine is very well represented; at the moment we have one post-doc researcher and three active PhD students (two others will obtain their degrees in 2025), so we look for talented young people interested in various aspects of logic: in 2025 we are especially interested in students willing to work in computability theory, reverse mathematics, Weihrauch reducibility (potential supervisor Alberto Marcone) and set theory, particularly large cardinals (potential supervisor Vincenzo Dimonte). The PhD students working in computability theory will be able to take advantage of the MSCA Staff Exchanges grant “New Frontiers for Computability” which funds mobility towards other universities involved in the project. 

The call for students starting in the fall is now open (deadline June 20, at 14 Italian time).

The English version can be found at https://www.uniud.it/en/research/do-research/doctorate-res/ammissione/modulistica/annexes-phd-call-2025/call-for-applications_41-cycle-university-of-udine.pdf

For administrative information contact dottorato.rice@uniud.it

For information about projects in the area of logic contact Alberto Marcone or myself.

Vincenzo Dimonte

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

Hebrew University Set Theory Seminar
Time: Wednesday, 28 May, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Yair Hayut
Title: Dense Ideals
Abstract: In this series of talks, I will present joint work with Monroe Eskew. The main result of our work is the relative consistency of the existence of dense ideals on all successors of regular cardinals simultaneously: namely, it is consistent that there is a -dense normal ideal on  for every cardinal  which is a successor of a regular cardinal. In particular, we show that it is consistent that for every <img height="9" width="41" src="https://ci3.googleusercontent.com/meips/ADKq_NZOHZq-dV0JH17ip8eCCwmfxEM_HnT0zFnUp4Xbm74bQpXHpKQBsCLQJXujWvfLktgbUZ4lxZwAyC32xdJdzqvc8bqig9xChtBgJLXbWANfP4jV4oPrCp1ciJvcGtr3Pj7BrA=s0-d-e1-ft#https://s0.wp.com/latex.php?zoom=3&bg=ffffff&fg=000000&s=0&latex=n%3C%5Comega&quot; alt="n, there exists an -dense ideal on , thus extending Foreman’s result for .
Beginning in the 1980s, Foreman proposed the philosophy of generic large cardinal axioms — a parallel hierarchy to the traditional large cardinal axioms. Unlike the classical axioms, these generic versions aim to settle set-theoretic questions about small cardinals, such as the Continuum Hypothesis. Just as large cardinals are characterized via combinatorial objects like measures, generic large cardinal axioms correspond to the existence of ideals with certain properties. One way to measure the strength of such an axiom is by how small the Boolean algebra of positive sets mod the ideal can be: the smaller, the better.
We begin by presenting a variant of Laver’s consistency proof for the existence of a saturated ideal. If time permits, we will also show that Martin’s Maximum implies the saturation of the non-stationary ideal on .
Later in the series, we will describe the classical construction of a dense ideal on  from an almost-huge cardinal. The main part of our work involves a new forcing notion — a variant of a construction introduced by Shioya. We iterate this forcing and, starting from a huge cardinal, produce a dense ideal on the successor of any regular cardinal.
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, 28 May, 13:00-14:00 local time (14:00-15:00 CEST)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

The University of Udine (NE Italy) is opening for new PhD positions in Mathematical and Physical Sciences:

Mathematical Logic in Udine is very well represented; at the moment we have one post-doc researcher and three active PhD students (two others will obtain their degrees in 2025), so we look for talented young people interested in various aspects of logic: in 2025 we are especially interested in students willing to work in computability theory, reverse mathematics, Weihrauch reducibility (potential supervisor Alberto Marcone) and set theory, particularly large cardinals (potential supervisor Vincenzo Dimonte). The PhD students working in computability theory will be able to take advantage of the MSCA Staff Exchanges grant “New Frontiers for Computability” which funds mobility towards other universities involved in the project. 

The call for students starting in the fall is now open (deadline June 20, at 14 Italian time).

The English version can be found at https://www.uniud.it/en/research/do-research/doctorate-res/ammissione/modulistica/annexes-phd-call-2025/call-for-applications_41-cycle-university-of-udine.pdf

For administrative information contact dottorato.rice@uniud.it

For information about projects in the area of logic contact Alberto or myself.

Vincenzo Dimonte

The fifth European Set Theory Colloquium will take place on Thursday, 22 May, at 17:00 central European summer time on zoom with the participants  
– Andrew Marks, University of California, Berkeley
– Grigor Sargsyan, Institute of Mathematics of the Polish Academy of Sciences 
– Dima Sinapova, Rutgers University 

The zoom information is: 
https://tuwien.zoom.us/j/66562462164?pwd=xy3MJCp8uWjeoASXZOb0tYLq65hJDa.1
Meeting-ID: 665 6246 2164; Password: 18NGuaU0

The colloquium is organised by Chris Lambie-Hanson, Sandra Müller, Philipp Schlicht and Zoltan Vidnyánszky. 
Please see  https://ests.wordpress.com/panel-discussions for the previous colloquia. 

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

Hebrew University Set Theory Seminar
Time: Wednesday, 21 May, 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, 21 May, 13:00-14:00 local time (14:00-15:00 CEST)
Speaker: Joel David Hamkins, University of Notre Dame
Title: Skolem’s paradox and the countable transitive submodel theorem
Abstract: One can find in the philosophical research literature surrounding Skolem’s paradox a certain claim, referred to as the transitive submodel theorem, according to which every transitive model of set theory admits a countable transitive submodel of the same theory. Although the statement may initially appear plausible—perhaps one thinks it follows from an application of the downward Löwenheim-Skolem theorem—nevertheless it turns out that as a mathematical claim, it is overstated. There is no such theorem. In this talk I shall give a full account of the countable transitive submodel proposition, taken as a principle of set theory, showing from suitable hypotheses that counterexamples are possible and characterizing exactly the circumstances in which the principle does hold. Ultimately, the countable transitive submodel proposition should be seen as a certain anti-large cardinal principle that is equiconsistent with but independent of ZFC and refuted by all the moderately strong large cardinal notions. This is joint work in progress with Timothy Button, with thanks to W. Hugh Woodin.
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Vienna Research Seminar in Set Theory
Time: Thursday, 22 May, 11:30-13:00 CEST
Speaker: William Chan, TU Wien
Title: Infinite Cardinal Exponentiation III
Abstract: In this 3 talk series (part 1, part 2, part 3: this part), we will discuss about the cardinality of familiar sets in choiceless universes possessing strong regularity properties. In particular, we will address the cardinality comparison between infinite cardinal exponentiation. As time permits, a deeper analysis of the cardinality for exponent omega which is the smallest nonwellorderable cardinal exponentiation will be considered.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 22 May, 15:00 – 15:50 CEST
Speaker: Y. Peresse, University of Hertfordshire
Title: Semigroups Of Generalised Symmetries
Abstract: The symmetries of a geometric shape X are the distance preserving functions f:X→X. Of course, the concept of symmetry extends well beyond Geometry and into virtually every area of Mathematics. For example, if X is a model-theoretic structure or a topological space, then its symmetries are the automorphisms and homeomorphisms of X, respectively. In each case, the symmetries of X form a subgroup of the symmetric group Sym(X) of all permutations of X.
There are two widely-studied and natural generalisations of the group Sym(X) to the world of semigroups. The Full Transformation Monoid XX consists of all functions f:X→X and the Symmetric Inverse Monoid consists of all bijections between subsets of X. These two semigroups correspond to two generalisations of the concept of symmetry as described above. For example, the group of automorphisms of a structure X is a subgroup of the semigroup of homomorphisms f:X→X(which is a subsemigroup of XX) and of the inverse semigroup of all isomorphisms between substructures of X (which is an inverse subsemigroup of IX).
In this talk, we will consider Sym(X), XX, and IX on an infinite set X. I will present a variety of results which highlight the connections between Semigroups on the one hand and Set Theory, Model Theory, and Topology on the other. No previous knowledge of Semigroup Theory will be assumed.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Fifth European Set Theory Society Colloquium
Time: Thursday, 22 May, 17:00-18:30 CEST
Speakers: Andrew Marks, University of California, Berkeley; Grigor Sargsyan, Institute of Mathematics of the Polish Academy of Sciences; Dima Sinapova, Rutgers University
Information: The zoom information for this colloquium is:
https://tuwien.zoom.us/j/66562462164?pwd=xy3MJCp8uWjeoASXZOb0tYLq65hJDa.1
Meeting-ID: 665 6246 2164, Passwort: 18NGuaU0

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

Hebrew University Set Theory Seminar
Time: Wednesday, 14 May, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Roy Shalev
Title: A dichotomy for transitive lists
Abstract: In the talk we will present a dichotomy statement concerning a class of transitive lists which at the level of  is a consequence of Martin’s Axiom and in fact follows both from  and from Martin’s Axiom for Y-c.c. posets.At the level of aleph_2, the consistency of the dichotomy with CH holds assuming the existence of a weakly compact cardinal. We show that the dichotomy at the level of lambda^+ has an impact on the structure of natural transitive objects. For example, we prove that it implies: every lambda^+-Aronszajne tree is special, every lambda^+-tower in (P(lambda),subseteq^*) is Hausdorff, the nonexistence of lambda^+-Souslin lower semi-lattices, the nonexistence of certain strongly unbounded colorings and the nonexistence of Todorcevic (lambda^+,lambda^+)-gaps in P(lambda).
Joint work with Borisa Kuzeljevic and Stevo Todorcevic.
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, 14 May, 13:00-14:00 local time (14:00-15:00 CEST)
Speaker: tba
Title: tba
Abstract: tba
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.

Caltech Logic Seminar
Time: Wednesday, 14 May, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CEST)  
Speaker: Clinton Conley, CMU
Title: Measurable 2-factors of regular bipartite graphs
Abstract: We consider the problem of finding a 2-regular subgraph of a given regular graph with no odd cycles. We show that this is always possible in the BP context. As a consequence, odd-regular bipartite Borel graphs on Polish spaces admit perfect matchings with the property of Baire, in contrast with recent examples of Kun in the measure-theoretic setting. Analogous results in the measure-theoretic context hold for hyperfinite graphs. This is joint work with Matt Bowen and Felix Weilacher, building upon prior joint work with Kechris and with Miller.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 15 May, 11:30-13:00 CEST
Speaker: W. Chan, TU Wien
Title: Infinite Cardinal Exponentiation II
Abstract: In this 3 talk series (part 1, part 2: this part, part 3), we will discuss about the cardinality of familiar sets in choiceless universes possessing strong regularity properties. In particular, we will address the cardinality comparison between infinite cardinal exponentiation. As time permits, a deeper analysis of the cardinality for exponent omega which is the smallest nonwellorderable cardinal exponentiation will be considered.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Set Theory in the UK
Time: Thursday, 15 May, 11:00-17:55 UK time CEST
Speakers: Dianthe Basak, Paris; Zaniar Ghadernezhad, Buckingham); Yurii Khomskii, Amsterdam
Information: The webpage of the meeting is https://www.dpmms.cam.ac.uk/~dbl25/STUK/16. The meeting will take place in hybrid format. Please contact Hope Duncan at mmhid@leeds.ac.uk in advance for the Teams link.

Vienna Logic Colloquium
Time: Thursday, 15 May, 15:00 – 15:50 CEST
Speaker: I. Ben-Yaacov, Universitè Claude Bernard Lyon 1
Title: Around affine logic
Abstract: Continuous logic is an extension of classical logic, allowing to replace the set of truth values {0,1} with the real line, and Bolean logical operations with continuous real-valued functions. Affine logic is a restriction of the latter to affine, rather than continuous connectives. This was suggested by Bagheri in a series of papers (referring to it as linear logic).
The restriction of the expressive power has the effect of endowing type spaces in affine logic with the structure of convex spaces, raising new questions regarding extremality: extreme types, extremal models (realising only extreme types), and decomposition of arbitrary models as integrals of extremal models. The restricted expressive power also poses new obstacles in our path when attempting to construct canonical parameters, and / or canonical bases in the context of stability. Finally, it is interesting to observe that Keisler randomisations, which were advanced at the time as natural examples of something we can do in continuous logic better than in classical logic, fit in fact much better in affine logic.
This is a joint work with Tomás Ibarlucía and Todor Tsankov.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

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

Leeds Set Theory Seminar
Time: Wednesday, 7 May, 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, 7 May, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Dima Sinapova, Rutgers University
Title: Forcing and Borel Equivalence Relations
Abstract: Analyzing when different generics for a given poset yield the same extension gives rise to countable Borel equivalence relations. We characterize when these relations are smooth. We also explore Prikry and Cohen forcing. This is joint work with Filippo Calderoni.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 8 May, 11:30-13:00 CET
Speaker: W. Chan, TU Wien
Title: Infinite Cardinal Exponentiation I
Abstract: In this 3 talk series (part 1: this part, part 2, part 3), we will discuss about the cardinality of familiar sets in choiceless universes possessing strong regularity properties. In particular, we will address the cardinality comparison between infinite cardinal exponentiation. As time permits, a deeper analysis of the cardinality for exponent omega which is the smallest nonwellorderable cardinal exponentiation will be considered.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 8 May, 15:00 – 15:50 CET
Speaker: H. Ben-Yami, Central European University, Vienna
Title: The Quantified Argument Calculus: Introduction and Research Directions
Abstract: The talk will present the Quantified Argument Calculus (Quarc): a logic system developed by Ben-Yami over the last decade, collaborating with a growing number of other philosophers and logicians.
Its basic departure from Frege’s logic is in its treatment of quantification: quantifiers are not sentential operators but connect to one place predicates to form arguments – quantified arguments – of other predicates. This departure is accompanied by others, and together they make Quarc closer to natural language in its syntax and the inferences it validates than is the first-order Predicate Calculus, while being at least as strong as the latter.
By now, Quarc comprises a family of closely related systems. On all or some of its versions, it has been shown to be sound and complete; to contain and validate Aristotle’s assertoric logic; it separates quantification from existence, shedding new light on logic’s ontological commitments, and lack thereof; it has been extended to modality, invalidating its analogues of the Barcan formulas; three-valued versions of it have been developed, capturing presupposition failure; additional quantifiers have been incorporated in it, such as “most” and “more”; several Quarc proof systems have been developed and its metalogical properties have been researched; decidability of Quarc fragments has also been researched; the image of the Predicate Calculus it contains shows in what sense quantification in the latter is restricted relative to Quarc’s; and more. Further research is currently being conducted, and there’s much potential in additional direction.
The purpose of the talk is both to introduce the audience to this burgeoning area of research, which has already produced more than a dozen publications by several researchers; and to indicate additional areas of promising research.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Cross-Alps Logic Seminar
Time: Friday, 9 May, 16.00-17.00 CEST
Speaker: M. Mazari-Armida, Baylor University
Title: A Baer-like criterion for relative injective modules via model theory
Abstract: Baer criterion is a classical result from module theory that asserts that to determine if a module is injective, it is enough to test for homorphisms coming from ideals of the ring. In this talk, we show that relative injective modules satisfy a similar criterion using model theory. More precisely, the result is obtained using independence relations which generalize Shelah’s non-forking to abstract elementary classes. This result is one of the first purely algebraic applications of independence relations to algebra in the context of AECs. We will introduce all the abstract elementary classes notions used in the talk and in parallel give a quick introduction to AECs of modules. The main result of the talk is joint work with J. Rosicky.
Information: The event will stream on the Webex platform. Please write to  luca.mottoros [at] unito.it  for the link to the event.

Toronto Set Theory Seminar
Time: Friday, 9 May, 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.

New York Logic Workshop
Time: Friday, 9 May, 14.00 New York time (20.00 CET)
Speaker: Charles Steinhorn, Vassar College
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.

Carnegie Mellon University Logic Seminar
Time: Tuesday, 29 May, 4:00 – 5:00pm Pittsburgh time (22:00 – 23:00 CET)
Speaker: Will Brian, UNC Charlotte
Title: The shift map on P(ω)/Fin
Abstract: I’m going to talk about an old question of van Douwen: Are the shift map and its inverse conjugate in the automorphism group of P(ω)/Fin? By the mid 1980’s, van Douwen and Shelah proved that it is consistent they are not conjugate. Specifically, any automorphism witnessing their conjugacy would need to be nontrivial (van Douwen), but it is consistent that all automorphisms are trivial (Shelah). In this talk I’m going to discuss the complementary result: it is consistent that the shift map and its inverse are conjugate and, in fact, it follows from CH.
Information: See the seminar webpage.

Hebrew University Set Theory Seminar
Time: Wednesday, 30 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, 30 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, 30 April, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Christian Rosendal, University of Maryland
Title: Continuity and strictness of measurable cocycles
Abstract: Several results regarding the topological and algebraic rigidity of maps and cocycles in the setting of Polish groups will be presented.
Firstly, suppose G is a Polish group acting continuously on a Polish space X, H is a Polish group and ψ:G×X→H is a cocycle that is continuous in the second variable. If ψ is either Baire measurable or is λ×μ-measurable with respect to Haar measure λ on G and a fully supported σ-finite Borel measure μ on X, then ψ is jointly continuous.
Secondly, if π:G→S is a map from a locally compact Polish group G into an abstract semigroup S and such that there is a conull subset Ω⊆G×G satisfying π(gf)=π(g)⋅π(f)for all (g,f)∈Ω, then there is a homomorphism ψ:G→S agreeing with π almost everywhere. A similar statement holds for Baire category and further developments will be discussed.
Information: See the seminar webpage.

Toronto Set Theory Seminar
Time: Friday, 2 May, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Luciano Salvetti Martinez
Title: On a class of CBERs defined on spaces of generics
Abstract: Given a countable model M of (a large fragment of) ZFC and a forcing poset in M, we say that two generic filters over M are equivalent if they produce the same generic extensions of M. This class of Countable Borel Equivalence Relations (CBERs) was first studied by Ian Smythe (2018). Many questions about which dynamical properties (e.g., hyperfiniteness, amenability) hold for CBERs in this class remain open. A particularly interesting open problem deals with whether this equivalence for Cohen generics is hyperfinite. It was shown by Smythe (2018) that such relation is a countable increasing union of hyperfinite CBERs. In the first half of this talk we will briefly discuss what is known about this class of CBERs in general and for particular forcing notions. In the second half we will prove that this equivalence of Cohen generics is hyperfinite on the set of Cohen generics that are mutually generic to a generic collapsing the continuum. The proof will involve Borel combinatorial arguments and avoid the generic hyperfiniteness theorem.
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 2 May, 14.00 New York time (20.00 CET)
Speaker: Nigel Pynn-Coates, University of Vienna
Title: Transserial tame pairs
Abstract: Interest in transseries and Hardy fields comes from several fields, including asymptotic analysis, dynamical systems, and model theory of the real numbers. The first-order theory of (logarithmic-exponential) transseries and maximal Hardy fields is completely axiomatized by the theory of closed H-fields, which is model complete, as Aschenbrenner, Van den Dries, and Van der Hoeven have shown in a long series of works. I will describe my extension of this model completeness to tame pairs of closed H-fields, in order to better understand large closed H-fields, such as maximal Hardy fields, hyperseries, or surreal numbers. Time permitting, I may mention ongoing work on differential-algebraic dimension in transserial tame pairs.
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.

Carnegie Mellon University Logic Seminar
Time: Tuesday, 22 April, 4:00 – 5:00pm Pittsburgh time (22:00 – 23:00 CET)
Speaker: David A. Fisher, Carnegie Mellon University
Title: The Logic of Property Based Types
Abstract: The logic of property based types (PBT) is a deductive logic that is sound for any imaginable domain. It is a finitely many-valued logic in which concepts represented by types serve as non-classical truth values. It is a pure calculus of types that combines certain benefits of propositional and higher-order logics. The design of PBT addresses questions about the nature of knowledge, truth, and existence. It is modeled after human deductive reasoning (HDR) and analogy with natural language. PBT logic is incomplete, intensional, precludes paradoxes, has less than exponential proof times, and like HDR, provides inference rules for abstraction, specialization, and generalization. It includes generalized forms of the law of the excluded middle (LEM), double negation elimination, and indirect proof.
Information: See the seminar webpage.

Hebrew University Set Theory Seminar
Time: Wednesday, 23 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, 23 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, 23 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.

New York Set Theory Seminar
Time: Friday, 25 April, 11.00 New York time (17.00 CET)
Speaker: Catalina Torres Pachon, University of Barcelona
Title: A Topological Approach to Characterising Hyperstationary Sets on Pκ(A)
Abstract: Given a topological space (X,τ), the derived set operator dτ maps a set T to its set of limit points with respect to τ. Fixing an initial topology τ0 on X, we can define a sequence of derived topologies (X,τ0,τ1,…,τξ,…), where τζ⊆τξ for ζ<ξ. This is achieved by declaring dτξ(T) to be open in τξ+1 and taking unions at limit stages. 
In Derived Topologies on Ordinals and Stationary Reflection, Bagaria characterised the non-isolated points in the ξ-th derived topology on ordinals as those satisfying a strong iterated form of stationary reflection, termed ξ-simultaneous reflection. 
Generalisations of combinatorial properties of ordinals to Pκ(A):={X⊆κ:|X|<κ}, where κ is an uncountable regular cardinal and A⊆κ, have been widely studied. In this context, we extend the notion of higher stationarity and construct a sequence of topologies ⟨τ0,τ1,…⟩ on Pκ(A), characterising the simultaneous reflection of high-stationary subsets of Pκ(A) in terms of elements in the base of a derived topology on Pκ(A).
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 25 April, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Luciano Salvetti Martinez
Title: On a class of CBERs defined on spaces of generics
Abstract: Given a countable model M of (a large fragment of) ZFC and a forcing poset in M, we say that two generic filters over M are equivalent if they produce the same generic extensions of M. This class of Countable Borel Equivalence Relations (CBERs) was first studied by Ian Smythe (2018). Many questions about which dynamical properties (e.g., hyperfiniteness, amenability) hold for CBERs in this class remain open. A particularly interesting open problem deals with whether this equivalence for Cohen generics is hyperfinite. It was shown by Smythe (2018) that such relation is a countable increasing union of hyperfinite CBERs. In the first half of this talk we will briefly discuss what is known about this class of CBERs in general and for particular forcing notions. In the second half we will prove that this equivalence of Cohen generics is hyperfinite on the set of Cohen generics that are mutually generic to a generic collapsing the continuum. The proof will involve Borel combinatorial arguments and avoid the generic hyperfiniteness theorem.
Information: Please see the seminar webpage for the login information.

New York Logic Workshop
Time: Friday, 25 April, 14.00 New York time (20.00 CET)
Speaker: Johanna Franklin, Hofstra University
Title: Failure modes for highness notions
Abstract: We say that a Turing degree is high in some context if it can always compute a correct answer given an input for which this is possible. When no correct answer is possible, however, what might such a degree do? We explore the possibilities in the context of computable structure theory. This is joint work with Wesley Calvert and Dan Turetsky.
Information: Please see the seminar webpage for the login information.