Online activities 20 – 26 January

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

Hebrew University Set Theory Seminar
Time: Wednesday, 22 January, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Haytham Hammud
Title: A maximal wide Aronszajn tree
Abstract: We shall discuss a paper of Omer Ben Neria, Menachem Magidor and Jouko Väänänen, which proves that if we assume the consistency of a weakly compact cardinal, then it’s consistent to have a model with a maximal wide Aronszajn tree. We shall construct the maximal tree, do an iterated forcing, and prove that the first step of the iteration is strongly proper and that our maximal tree stays maximal after the first part of the iteration.
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, 22 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, 22 January, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Asger Törnquist, University of Copenhagen
Title: Π11 maximal almost disjoint families and Laver measurability
Abstract: A result due to Schrittesser and the speaker states:
Theorem 1: If Γ is a somewhat “reasonable” class of subsets of Baire space which have the properties:
(1) All sets are completely Ramsey (i.e., Baire measurability w.r.t. the Ellentuck topology); and
(2) Uniformization (even just on Ramsey positive sets);
then there can’t be any infinite maximal almost disjoint (“mad”) families in Γ.
The question arises if we can replace (1) by Laver measurability (in the sense of A. Miller), i.e.
(1′) Every set in Γ either contains the set of branches through a Laver tree, or it avoids all branches through a Hechler tree.
In this talk, I will show this is not the case by constructing a Π11 infinite mad family in the Laver forcing extension of L (noting here that the class Π11 has uniformization, and by a result of A. Miller (1′) holds in the in the Laver forcing extension of L).
The reason this is interesting (to me, at least) is that this shows that despite a number of similarities between generic reals for Laver and Ramsey measurability (and Laver and Mathias forcing), Laver can’t replace Ramsey in the proof of Theorem 1.
This is joint work with David Schrittesser.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 23 January, 11:30-13:00 CET
Speaker: T. van der Vlugt, TU Wien
Title: Rearrangement & subseries numbers
Abstract: By rearranging the terms of a conditionally convergent series we can make it assume a different limit or even make it divergent. Similarly we could do so by taking a subseries of a conditionally convergent series. The rearrangement (and subseries) numbers are the least number of permutations (or subsets) of indices that are needed to change the behaviour of every conditionally convergent series. The rearrangement and subseries numbers are cardinal characteristics (cardinalities that are bound between ℵ1 and the size of the continuum 2ℵ0).
In this talk we showcase various general tools (relational systems, Tukey connections, forcing) that are useful in the study of cardinal characteristics, we will give an overview of the family of rearrangement and subseries numbers, we will compare them to various well-known other cardinal characteristics, and we will introduce dual rearrangement and subseries number.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 23 January, 15:00 – 15:50 CET
Speaker: tba
Title: tba
Abstract: tba
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 23 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.

Series of talks on the Aspero-Golshani paper “The special Aronszajn tree property at $\aleph_2$ and GCH”

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Following feedback from colleagues, we are planning to give a series of online talks on our paper above. In these talks we will go through the paper in detail, covering all points in the proof.

We would like to start the last week of January (tentatively on Thursday 30th at 3pm UK time) or the week after.

The talks will be on zoom. They will be recorded. 

If you are interested in attending, please send me an email in the next couple of weeks to d.aspero@uea.ac.uk so I can send you the details.

Online activities 13 – 19 January

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

Leeds Set Theory Seminar
Time: Wednesday, 15 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, 15 January, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Andy Zucker, Waterloo
Title: Topological groups with tractable minimal dynamics
Abstract: In joint work with Gianluca Basso, we explore the class of Polish groups whose universal minimal flows admit a comeager orbit. By work of Ben Yaacov, Melleray, and Tsankov, this class contains all Polish groups with metrizable universal minimal flow, and by an example of Kwiatkowska, this inclusion is strict. We isolate the correct generalization of this class of Polish groups to the class of all topological groups. We call these the topological groups with “tractable minimal dynamics (TMD).” One way of phrasing what makes this class “tractable” is an “abstract Kechris-Pestov-Todorcevic correspondence” which characterizes membership in TMD using a Ramsey-theoretic property of the group. In particular, this implies that TMD is absolute between models of set theory. We also state some conjectures to the effect that any topological group not in TMD has “wild” minimal dynamics.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 16 January, 11:30-13:00 CET
Speaker: W. Dai, Nankai University, Tianjin, China
Title: Universal Δ-metric spaces, Hall’s group and Lévy groups
Abstract: In this talk, we study the isometry group Iso(UΔ) of the Δ-metric Urysohn space UΔ equipped with the pointwise convergence topology for a countable distance set Δ with infΔ=0. We showed that Iso(UΔ) is a Lévy group, so it is extremely amenable. Moreover, we can choose the Lévy family such that its increasing union is isomorphic to Hall’s group. This generalizes the results that Iso(U) is Lévy by Pestov and Iso(UΔ) contains a dense subgroup which is isomorphic to Hall’s group by Etedadialiabadi, Gao, Le Maître and Melleray. Then we will discuss its analogy for the continuous logic case.
It is an ongoing project with Su Gao and Víctor Hugo Yañez.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 16 January, 15:00 – 15:50 CET
Speaker: J. Grebik, Masaryk University, Brno
Title: Discrete and continuous translational monotilings
Abstract: In this talk, I will survey results about translational monotilings of Zd and Rd, with a particular focus on the case d≤2. One of the central questions in this area is the decidability of the tiling problem. Closely related is the periodic tiling conjecture (PTC), which has been confirmed in Z2 by Bhattacharya but was recently disproved in high dimensions by Greenfeld and Tao. For R2, analogous questions remain open, even for polygonal sets. The most general result here is due to Kenyon, who established that PTC holds for topological disks. In ongoing work with de Dios Pont, Greenfeld, and Madrid, we show that translational monotilings by axis-parallel polygonal sets satisfy a weaker version of PTC and derive a decidability result in this context.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 16 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.

Cross-Alps Logic Seminar
Time: Friday, 17 January, 16.00-17.00 CEST
Speaker: J. Väänänen, University of Helsinki
Title: Categoricity arguments and their philosophical uses
Abstract: Both number theory and set theory have a claim to categoricity, in one form or another, when axiomatized in second order logic. This goes back to Dedekind and Zermelo. It is less well-known that such claims manifest themselves also in first order axiomatizations, however non-categorical such axiomatizations are in the usual setup of mathematical logic (Vaananen, “An extension of a theorem of Zermelo”. BSL, 2019). Parsons and others have written about this e.g. in Parsons, “The uniqueness of the natural numbers” (Jerusalem Philosophical Quarterly, 1990), and Button and Walsh, “Philosophy and Model Theory”. (Oxford University Press, 2018). We claim that philosophical uses of these arguments do not carry the philosophical weight they are purported to do. To support our claim we analyse the categoricity arguments in detail in the context of both first and second order logic. We expose a common factor of such arguments, internal categoricity, namely categoricity within what the theory in question, be it number theory or set theory, can see. While internal categoricity is a remarkable phenomenon in itself, we argue that it cannot be used to defend the decidability of formal statements in the theory. In conclusion, when categoricity results are used to make certain philosophical claims, even though the categoricity results are by and large correct, they do not support those claims. Reference: Maddy and Vaananen: Philosophical Uses of Categoricity Arguments, Elements in the Philosophy of Mathematics. Cambridge University Press. (2023).
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, 17 January, 11.00 New York time (17.00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 17 January, 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, 17 January, 14.00 New York time (20.00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

Online activities 6 – 12 January

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

Kobe Set Theory Seminar
Time: Wednesday, 8 January, 15:30 local time (07:30 CET)
Speaker: cancelled
Title: cancelled
Abstract: cancelled
Information: See the seminar webpage.

Hebrew University Set Theory Seminar
Time: Wednesday, 8 January, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Eyal Kaplan
Title: Hamkins’ cover and approximation properties and iterations of Prikry-type forcings
Abstract: The cover and approximation properties were discovered and studied by Hamkins. Typical applications of those properties are proofs that certain ultrafilters, extenders or elementary embeddings, which are defined in forcing extensions, are amenable to the ground model.
We prove that iterations of Prikry-type forcings satisfy the \kappa-cover and \kappa-approximation properties, where \kappa is the length of the iteration, it is inaccessible, GCH holds, and the Prikry-type forcings participating in the iteration satisfy relatively mild additional assumptions. This is part of a joint work with Moti Gitik.
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, 8 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.

Vienna Research Seminar in Set Theory
Time: Thursday, 9 January, 11:30-13:00 CET
Speaker: Natasha Dobrinen, University of Notre Dame
Title: Forcing on coding trees
Abstract: In this talk, we will present Harrington’s forcing proof of the Halpern-Läuchli Theorem and extensions to coding trees representing Fraïssé limits of free amalgamation (and certain strong amalgamation) classes with the Ramsey property. We will discuss several versions of such forcings and their various applications to infinite structural Ramsey theory.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 9 January, 15:00 – 15:50 CET
Speaker: Natasha Dobrinen, University of Notre Dame
Title: Infinite structural Ramsey theory and logic
Abstract: The infinite Ramsey theorem states that given any coloring of all pairs of natural numbers into two colors, there is an infinite subset of natural numbers in which all pairs have the same color. When moving from sets to relational structures, some surprising phenomena occur: The prototypical example is that there is a coloring of pairs of rational numbers into two colors such that both colors persist in any subset of the rationals forming a dense linear order (Sierpiński, 1933). Likewise for colorings of edges in the Rado graph (Erdős–Hajnal–Pósa, 1975). The study of optimal bounds for finite colorings of copies (or embeddings) of a finite substructure inside an infinite structure is the subject of big Ramsey degrees. Optimal bounds are connected with structural expansions which produce analogues of the infinite Ramsey theorem; the pursuit of the optimal structural expansions has led to new connections between logic and structural Ramsey theory.
This talk will introduce big Ramsey degrees, key examples, and components intrinsic to their characterizations, and touch on infinite-dimensional structural Ramsey theory ties in with topological Ramsey spaces. We will discuss various proof methods, including Milliken’s strong tree theorem, Harrington’s forcing proof of the Halpern-Läuchli Theorem, coding trees and forcing Ramsey theorems on them, parameter words, and others.
The motivation for and progress of Ramsey theory on infinite structures are intrinsically intertwined with problems and methods in logic, including first-order logic, set theory, model theory, and computability theory. The expository paper [1] provides a gentle introduction to infinite structural Ramsey theory and an overview of the area. A plethora of other references will be included in the talk.
[1] N. Dobrinen, “Ramsey theory of homogeneous structures: Current trends and open problems”. 2022 ICM—International Congress of Mathematicians. Vol. 3. Sections 1–4,1462–1486. Edited by D. Beliaev and S. Smirnov, EMS Press, Berlin, 2023.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Baltic Set Theory Seminar
Time: Thursday, 9 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, 10 January, 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, 10 January, 14.00 New York time (20.00 CET)
Speaker: Jouko Väänänen, University of Helsinki
Title: Categoricity arguments and their philosophical uses
Abstract: Both number theory and set theory have a claim to categoricity, in one form or another, when axiomatized in second order logic. This goes back to Dedekind and Zermelo. It is less well-known that such claims manifest themselves also in first order axiomatizations, however non-categorical such axiomatizations are in the usual setup of mathematical logic (Väänänen, ‘An extension of a theorem of Zermelo’ BSL, 2019). Parsons and others have written about this e.g. in Parsons, ‘The uniqueness of the natural numbers’ (Jerusalem Philosophical Quarterly, 1990), and Button and Walsh, ‘Philosophy and Model Theory’ (Oxford University Press, 2018). We claim that philosophical uses of these arguments do not carry the philosophical weight they are purported to do. To support our claim we analyse the categoricity arguments in detail in the context of both first and second order logic. We expose a common factor of such arguments, internal categoricity, namely categoricity within what the theory in question, be it number theory or set theory, can see. While internal categoricity is a remarkable phenomenon in itself, we argue that it cannot be used to defend the decidability of formal statements in the theory. In conclusion, when categoricity results are used to make certain philosophical claims, even though the categoricity results are by and large correct, they do not support those claims. 
Reference: Maddy and Väänänen: Philosophical Uses of Categoricity Arguments, Elements in the Philosophy of Mathematics. Cambridge University Press. (2023). 
Information: Please see the seminar webpage for the login information.

Online activities 30 December – 5 January

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

Hebrew University Set Theory Seminar
Time: Wednesday, 1 January, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Inbar Oren
Title: Indecomposable ultrafilters and collapsing successors of singular cardinals
Abstract: In a famous paper by Ben David and Magidor, they show the existence of an (\aleph_0,\aleph_\omega)-indecomposable ultrafilter on \aleph_{\omega+1}, in an intermediate model of a forcing that collapses \aleph_{\omega+1}. This is an indication that an (\aleph_0,\aleph_\omega)-indecomposable ultrafilter on \aleph_{\omega+1} might be enough to collapse \aleph_{\omega+1} by a forcing extension.
I will show that if \lambda is a singular cardinal, strong limit and there is an (\aleph_0,\lambda)-indecomposable ultrafilter on \lambda^+, then there is a \lambda^{++} c.c. forcing notion that collapses \lambda^+ and preserves \lambda.
As a corollary we will get that there can’t be a (\aleph_0,\lambda)-indecomposable ultrafilter on  \lambda^+ if \omega_1″>, in partcular there is no  (\aleph_0,\aleph_{\omega_2})-indecomposable ultrafilter on \aleph_{\omega_2+1}.
Information: This talk will be given in hybrid format. Please contact Omer Ben-Neria and Inbar Oren for the login information.

Online activities 16 – 22 December

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

Hebrew University Set Theory Seminar
Time: Wednesday, 18 December, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Tanmay Inamdar
Title: Galvin’s conjecture
Abstract: I will prove that for every colouring of pairs of reals with finitely-many colours, there is a set homeomorphic to the rationals on which at most two colours are realised. This was conjectured by Galvin in 1970, and a colouring of Sierpiński from 1933 witnesses that the number of colours cannot be reduced to one. 
Previously Shelah had shown that a stronger statement is consistent with a forcing construction assuming the existence of large cardinals (in 1985 from an w1-Erdos cardinal, later in 1992 just a strongly Mahlo cardinal). Then in 2018 Raghavan and Todorčević had proved it axiomatically (from a Woodin cardinal, or a strongly compact cardinal, or a precipitous ideal on w1), improved later by Eisworth (a Ramsey cardinal). I will prove it in ZFC.
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, 18 December, 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.

Online activities 9 – 15 December

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

Kobe Set Theory Seminar
Time: Wednesday, 11 December, 15:30 local time (7:30 CET)
Speaker: Jörg Brendle
Title: Combinatorial properties of MAD families, Part I
Abstract: I will present some results on strong combinatorial properties of MAD families, like (strong) tightness, the Shelah-Steprans property and the raving property. these properties are related to indestructibility of MAD families under some forcing notions. this is joint work with Osvaldo Guzmán, Michael Hrušák, and Dilip Raghavan.
Information: See the seminar webpage.

Hebrew University Set Theory Seminar
Time: Wednesday, 11 December, 13:00-15:00 local time (12:00-14:00 CEST) 
Speaker: Yifan Yang
Title:  An Abstract Framework for Several Prikry-Type Forcings, Part II
Abstract: Since the original Prikry forcing was invented, a large number of new forcing notions, more sophisticated while sharing some common spirit with the original Prikry forcing, has been invented, which are often referred to as “Prikry-type forcings”. In this talk I would present an abstract framework called “graded forcings” which covers quite a few Prikry-type forcings. I will show how arguments of several key properties of various Prikry-type forcings (like the Prikry property) can be summarized uniformly in this framework, and then present examples of how several concrete Prikry-type forcings fit into this framework. I’ll also remark on the limitations of this framework.
Information: This talk will be given in hybrid format. Please contact Omer Ben-Neria and Inbar Oren for login information.

Leeds Set Theory Seminar
Time: Wednesday, 11 December, 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.

Kobe Set Theory Seminar
Time: Thursday, 12 December, 15:30 local time (7:30 CET)
Speaker: Jörg Brendle
Title: Combinatorial properties of MAD families, Part II
Abstract: I will present some results on strong combinatorial properties of MAD families, like (strong) tightness, the Shelah-Steprans property and the raving property. these properties are related to indestructibility of MAD families under some forcing notions. this is joint work with Osvaldo Guzmán, Michael Hrušák, and Dilip Raghavan.
Information: See the seminar webpage.

New York Set Theory Seminar
Time: Friday, 13 December, 11.00am New York time (17.00 CET)
Speaker: tba
Title: tba
Abstract: tba
Information: Please see the seminar webpage for the login information.

Toronto Set Theory Seminar
Time: Friday, 13 December, 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. 

Cross-Alps logic seminar (online) today at 16:00

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Dear all,

On Friday 06.12.2024 at 16.00 CET

Mai Gehrke (Université Côte d’Azur) 

will give a talk on 

Introduction to Stone, Priestley, and the Omega-Point dualities and some generalisations

Please refer to the usual webpage of our LogicGroup for more details and the abstract of the talk.

The seminar will be held remotely through Webex. Please contact Vincenzo Dimonte and Luca Motto Ros in advance for information to access the meeting.

The Cross-Alps Logic Seminar is co-organized by the logic groups of Genoa, Lausanne, Turin and Udine as part of our collaboration in the project PRIN 2022 ‘Models, Sets and Classifications’. 

All the best,

Vincenzo Dimonte

Online activities 2 – 8 December

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

Leeds Set Theory Seminar
Time: Wednesday, 4 December, 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, 4 December, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)  
Speaker: Clark Lyons, Eötvös Loránd University and Alfréd Rényi Institute of Mathematics
Title: Construction and obstruction results in Baire measurable combinatorics
Abstract: Techniques in measurable combinatorics for solving graph labeling problems almost everywhere on a Borel graph are often adaptable to solve these problems on a comeager set. For example, Brandt, Chang, Grebík, Grunau, Rozhoň, and Vidnyánszky showed that every locally checkable labeling problem (LCL) admitting a mod-null solution on any dd-regular acyclic Borel graph also admits a mod-meager solution on every such graph. Also, some results showing that measure-expansive pmp graphs have measurable perfect matchings have analogs in the Baire-measurable setting.
Despite this, there is an LCL which always admits a measurable solution on any Schreier graph of a free Borel action of Z^2 but does not always admit a Baire measurable solution. This talk will discuss the methods used in these Baire measurable construction and obstruction results as well as the method of rectangular toast for constructing measurable labelings on grids. This includes joint work with Alexander Kastner as well as with Katalin Berlow, Anton Bernshteyn, and Felix Weilacher.
Information: See the seminar webpage.

Vienna Research Seminar in Set Theory
Time: Thursday, 5 December, 11:30-13:00 CET
Speaker: P. Marun, Czech Academy of Sciences, Prague
Title: Labelled sets
Abstract: A theorem of Dilworth asserts that, if a poset P has no antichains whose size is larger than m, where m is a natural number, then P can be written as a union of m many chains. If m is instead an infinite cardinal, then the analogous statement is false, counterexamples were constructed by Perles. In recent work, Abraham and Pouzet gave a basis for the class of such counterexamples, and asked if it could be somewhat simplified. Labelled sets arise in connection with these counterexamples. We show that, when the underlying sets are ℵ1-dense, then any two labelled sets embed into each other. 
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Vienna Logic Colloquium
Time: Thursday, 5 December, 15:00 – 15:50 CET
Speaker: W. Chan, TU Wien
Title: Basis results for uncountable linear orders
Abstract: This talk will discuss finite basis results for classes of uncountable linear orderings of size above familiar cardinalities under order embeddings.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.

Toronto Set Theory Seminar
Time: Friday, 6 December, 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. 

2-year research assistant position (renewable up to 5 years) in logic, Bologna – deadline 30 November!

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2-year research assistant position (renewable up to 5 years) in logic at the Department of Mathematics at the University of Bologna funded by the ERC grant “Definable Algebraic Topology”.

https://bandi.unibo.it/ricerca/assegni-ricerca?id_bando=68580

The application deadline is November 30.

Notice that holding a PhD is not a necessary eligibility requirement, and holding a masters degree is sufficient.

Best,

Martino Lupini