The weekly announcements will be moved to the new website https://settheory.eu soon.
Carnegie Mellon University Logic Seminar
Time: Tuesday, 11 November, 4:00 – 5:00pm Pittsburgh time (22:00 – 23:00 CET)
Speaker: Tom Benhamou, Rutgers University
Title: On idempotency and the Canjar-Laflamme conjecture
Abstract: Canjar and Laflamme studied strong p-point ultrafilters on \omega and conjectured that in the class of p-points, these are exactly those which are not RK-reducible to a rapid ultrafilter. While this conjecture has been refuted by Blass-Hrusak-Verner, we provide a characterization of Canjar ultrafilters that captures the underlying intuition behind the conjecture, which we formulate using the Tukey order. We connect this to Tukey idempotency and present several applications of our characterization, including an answer to a question of Hrusak-Verner regarding generic ultrafilters obtained by quotients over definable ideals. This is joint work with Natasha Dobrinen and Tan Ozalp.
Information: See the seminar webpage.
Hebrew University Set Theory Seminar
Time: Wednesday, 12 November, 13:00-15:00 local time (12:00-14:00 CET)
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, 12 November, 13:00-14:00 local time (14:00-15:00 CET)
Speaker: Sylvy Anscombe, Université Paris Cité
Title: Fragments of theories of tame valued fields
Abstract: F-V Kuhlmann’s theory of tame (and separably tame) valued fields is one of the most general settings in which we have AKE principles. Such principles come in many flavours; in particular, we may constrain our attention to certain “subfragments” of the languages of valued fields/rings/ordered abelian groups. I will explain some of the underlying algebra, and show some recent work on such principles in expansions by sections of the residue map. This will touch on (separate) projects with Boissonneau and Fehm.
Information: Contact Hope Duncan at mmhid@leeds.ac.uk for more information.
Caltech Logic Seminar
Time: Wednesday, 12 November, 12:00 – 13:00pm Pacific time (21:00 – 22:00 CET)
Speaker: Josh Frisch, UCSD
Title: Minimal Subdynamics: Descriptive ideas about Dynamical Questions
Abstract: Let Γ be a countably infinite discrete group. A Γ-flow X (i.e., a nonempty compact Hausdorff space equipped with a continuous action of Γ) is called S-minimal for a subset S⊆Γ if the partial orbit S⋅x is dense for every point x∈X. (When S=Γ, we recover the usual notion of minimality.) Despite the simplicity of the definition, given a group Γ, finding an S-minimal dynamical system is typically quite difficult (in particular even when Γ is the free group and S is a subgroup it was not previously known).
In this talk, I will discuss a very recent result on how to construct S-minimal systems for any countable collection of infinite subsets simultaneously. Although the problem is purely dynamical, the techniques make heavy use of recent ideas from descriptive set theory. Indeed, once the main result is established, we can return to derive some non-obvious, purely Borel, corollaries. This is joint work with Anton Bernshteyn.
Information: See the seminar webpage.
Vienna Research Seminar in Set Theory
Time: Thursday, 13 November, 11:30-13:00 CET
Speaker: Stefan Hoffelner, TU Wien
Title: Forcing Global Sigma-Uniformization in Various Contexts (part 1)
Abstract: Global Σ-uniformization is a striking regularity property for projective sets of reals. Until recently, the only known method for obtaining it relied on the existence of a good projectively definable well-ordering of the reals. Consequently, the global Σ-uniformization property appeared to be confined to a rather limited class of universes.
In this talk, I will present a forcing technique that yields models satisfying global Σ-uniformization. The method is highly flexible and can be adapted to produce a wide range of universes in which global Σ-uniformization coexists with other desirable or surprising features. In particular, I will show how to force BPFA together with global Σ-uniformization—a result that contrasts sharply with the situation under PFA, which implies PD and thus the familiar zig-zag pattern governing the uniformization property
This is the first part of a series of 3 talks; the next 2 talks will take place on November 20 and November 27.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.
Vienna Logic Colloquium
Time: Thursday, 13 November, 15:00 – 15:50 CET
Speaker: A. Fornasiero, University of Florence
Title: Generic derivations and algebraically bounded structures
Abstract: Let K be a monster model of an algebraically bounded theory expanding a field of characteristic 0. We show that K admits a generic derivation δ. (K,δ) inherits many of the model theoretic properties of K: if K is simple/stable/NIP then (K,δ) also is. Moreover, if K has a “reasonable” definable topology, then K is the open core of (K,δ). Being algebraically bounded (or more generally, a geometric expansion of a field) imposes severe constraints on K. If K is stable, then K is a pure algebraically closed field (and (K,δ) is a differentially closed field). If K is simple, then it is supersimple of rank 1 (and (K,δ) is supersimple of rank ω). If both K and (K,δ) have geometric elimination of imaginaries, then (K,δ) is superrosy of rank ω.
Joint works with G. Terzo, E. Kaplan, A. Matthews.
Information: This talk will be given in hybrid format. Please contact Petra Czarnecki for information how to participate.
New York Set Theory Seminar
Time: Friday, 14 November, 11.00 New York time (17.00 CET)
Speaker: Andrew Brooke-Taylor, University of Leeds
Title: tba
Abstract: tba
Information: Please see the seminar webpage.
Toronto Set Theory Seminar
Time: Friday, 14 November, 1.30-3.00pm Toronto time (19.30-21.00 CET)
Speaker: Diego Bejarano Rayo, York University
Title: tba
Abstract: tba
Information: Please see the seminar webpage.
New York Logic Workshop
Time: Friday, 14 November, 14.00 New York time (20.00 CET)
Speaker: Dan Turetsky, Victoria University of Wellington
Title: Iterated derivatives and antiderivatives of graphs
Abstract: The Hausdorff derivative of a linear order can be iterated to an ordinal length, giving a sequence of quotient linear orders, where each step requires a double jump to calculate.. Ash and Watnick give a converse to this, where the antiderivatives are product orderings of an appropriate lower complexity than the original ordering. Motivated by uncountable computability theory, we wanted a variant of this in which the derivatives are substructures rather than quotient structures. Once we had this, it turned out to apply not just to linear orders, but also graphs, trees and forests. I will explain our theorem primarily in the context of countable graphs and computability theory, but with some asides about other structures and uncountable computability theory.
Information: Please see the seminar webpage.
-directed well-founded partial order, 
there is a c.c.c.-forcing notion that adds an ultrafilter on 
with a basis which is order isomorphic (with inclusion up to a bounded error) to 
-Aronszajn trees as topological spaces under the interval topology.
Archive of the European Set Theory Society 