The Leeds Models and Sets seminar series is now run by Ibrahim Mohammed and Carla Simons, and its webpage can be found here.

Here are a list of some previous seminars – for upcoming talks please see the Leeds webpage.

14th June 2022
Speaker: Daisuke Ikegami, Shibaura Institute of Technology
Title: On preserving AD via forcings

Abstract: It is well-known that forcings preserve \mathsf{ZFC}, i.e., any set generic extension of any model of \mathsf{ZFC} is again a model of \mathsf{ZFC}. How about the Axiom of Determinacy (\mathsf{AD}) under \mathsf{ZF}? It is not difficult to see that Cohen forcing always destroys \mathsf{AD}, i.e., any set generic extension of a model of \mathsf{ZF}+ \mathsf{AD} via Cohen forcing is not a model of \mathsf{AD}. Actually it is open whether there is a forcing which adds a new real while preserving \mathsf{AD}. In this talk, we present some results on preservation & non-preservation of \mathsf{AD} via forcings, whose details are as follows:
1. Starting with a model of \mathsf{ZF} + \mathsf{AD}^{+} + V = L(P(R)), any forcing increasing \Theta destroys \mathsf{AD}.
2. It is consistent relative to \mathsf{ZF} + \mathsf{AD}_R that \mathsf{ZF} + \mathsf{AD}^{+} + There is a forcing which increases \Theta while preserving \mathsf{AD}.
3. In \mathsf{ZF}, no forcings on the reals preserve \mathsf{AD}. (This is an improvement of the result of Chan and Jackson where they additionally assumed \Theta is regular.)
4. In \mathsf{ZF} + \mathsf{AD}^{+} + V = L(P(R)) + \Theta is regular, there is a forcing on \Theta which adds a new subset of \Theta while preserving AD.
This is joint work with Nam Trang.

7th June 2022
Speaker: Lorna Gregory, Università degli Studi della Campania Luigi Vanvitelli
Title: Decidability of Theories of Modules of Prüfer domains


Abstract: An integral domain is Prüfer if its localisation at each maximal ideal is a valuation domain. Many classically important rings are Prüfer domains. For instance, they include Dedekind domains and hence rings of integers of number fields; Bézout domains and hence the ring of complex entire functions and the ring of algebraic integers; the ring of integer valued polynomials with rational coefficients and the real holomorphy rings of formally real fields.
Over the last 15 years, efforts have been made to characterise when the theory of modules of (particular types of) Prüfer domains are decidable. I will give an overview of such decidability results culminating in recently obtained elementary conditions completely characterising when the theory of modules of an arbitrary Prüfer domain is decidable.

31st May 2022
Speaker: Omer Ben-Neria, Hebrew University of Jerusalem
Title: Diamonds, Compactness, and Global Scales


Abstract:  In pursuit of an understanding of the relations between compactness and approximation principles we address the question:  To what extent do compactness principles assert the existence of a diamond sequence? It is well known that a cardinal \kappa that satisfies a sufficiently strong compactness assumption must also carry a diamond sequence. However, other results have shown that certain weak large cardinal assumptions are consistent with the failure of the full diamond principle. We will discuss this gap and describe recent results with Jing Zhang which connect this problem to the existence of a certain global notion of cardinal arithmetic scales.

24th May 2022
Speaker: Juvenal Murwanashyaka, University of Oslo
Title: Weak Essentially Undecidable Theories of Concatenation


Abstract: We sketch a proof of mutual interpretability of Robinson arithmetic and a weak finitely axiomatized theory of concatenation.

17th May 2022
Speaker: Julia Knight, University of Notre Dame
Title: Freeness and typical behavior for algebraic structures

Abstract: The talk is on joint work with Johanna Franklin and Turbo Ho.  Gromov asked “What is a typical group?”  He was thinking of finitely presented groups.  He proposed an approach involving limiting density.  In 2013, I conjectured that for elementary first order sentences \varphi, and for group presentations with n generators (n\geq 2) and a single relator, the limiting density for groups satisfying \varphi always exists, with value 0 or 1, and the value is 1 iff \varphi is true in the non-Abelian free groups.  The conjecture is still open, but there are positive partial results by Kharlampovich and Sklinos, and by Coulon, Ho, and Logan.  We ask Gromov’s question about structures in other equational classes, or algebraic varieties in the sense of universal algebra.  We give examples illustrating different possible behaviors.  Focusing on languages with just finitely many unary function symbols, we prove a result with conditions sufficient to guarantee that the analogue of the conjecture holds.  The proof uses a version of Gaifman’s Locality Theorem, plus ideas from random group theory and probability. 

10th May 2022
Speaker: Diana Carolina Montoya, Kurt Gödel Research Center for Mathematical Logic
Title: Higher independence at regular cardinals.


Abstract: In the first part of this talk I will introduce the classical concept of a maximal independent family and its main properties. The second part of the talk will be devoted to deal with the generalisation of independence for regular uncountable cardinals. I will show the differences and similarities with the classical setting, as well as new lines of research that appear when dealing with this generalisation.
Finally,  I will mention some recent results of Vera Fischer and myself regarding independence.

3rd May 2022
Speaker: Noa Lavi, Hebrew University of Jerusalem
Title: New irreducible generalised power series


Abstract: A classical tool in the study of real closed fields are the fields K((G)) of generalised power series (i.e., formal sums with well-ordered support) with coefficients in a field K of characteristic 0 and exponents in an ordered abelian group G. A fundamental result of Berarducci ensures the existence of irreducible series in the subring K((G\le0)) of K((G)) consisting of the generalised power series with non-positive exponents.  We generalize previous results and show that for certain order types almost all series are irreducible or irreducible up to a monomial.

26th April 2022
Speaker: Tamara Servi, IMJ-PRG & Fields Institute
Title: Interdefinability and compatibility in certain o-minimal expansions of the real field

Abstract: The sets definable in an o-minimal expansion of the real field have a tame topological behaviour (uniform finiteness, good dimension theory, no pathological phenomena). Being able to tell if a certain real set or function is definable in a given o-minimal structure gives us information on how tame the geometry of that object is.
Let us say that a real function f is o-minimal if the expansion (R,f) of the real field R by f is o-minimal. A function g is definable from f if g is definable in (R,f). Two o-minimal functions f and g are compatible if (R,f,g) is o-minimal. I will discuss the o-minimality, the interdefinability and the compatibility of two special functions, Euler’s Gamma and Riemann’s Zeta, restricted to the reals. Joint work with J.-P. Rolin and P. Speissegger.

29th March 2022 – will be at 15:45-16:55 BST
Speaker: Kameryn J Williams, Sam Houston State University
Title: The potentialist multiverse of classes

22nd March 2022
Speaker: Asaf Karagila, University of East Anglia
Title: Ccc without C, si? Si.

15th March 2022
Speaker: Fan Yang, University of Helsinki
Title: Dependence logic and its axiomatization problem

8th March 2022
Speaker: Sandra Müller, Technische Universität Wien
Title: The Interplay of Determinacy, Large Cardinals, and Inner Models

1st March 2022
Speaker: Victoria Noquez, Indiana University
Title: The Sierpinski Carpet as a Final Coalgebra

22nd February 2022
Speaker: Itay Kaplan, Hebrew University of Jerusalem
Title: On large externally definable subsets in NIP

15th February 2022
Speaker: Hirotaka Kikyo, Kobe University
Title: On some generic structures

8th February 2022
Speaker: Vera Fischer, Universität Wien
Title: Spectra and definability

1st February 2022
Speaker: Zoé Chatzidakis, École Normale Supérieure – CNRS
Title: Measures on perfect PAC fields

25th January 2022
Speaker: Andrew Brooke-Taylor, University of Leeds
Title: Products of CW complexes

18th January 2022
Speaker: Pantelis Eleftheriou, University of Leeds 
Title: Pillay’s Conjecture for groups definable in weakly o-minimal non-valuational structures

15th December 2021 – moved from 1st December
Speaker: Aris Papadopoulos, University of Leeds
Title: Around Generalised Indiscernibles and Higher-arity Independence Properties

8th December 2021
Speaker: Anush Tserunyan, McGill University
Title: Backward ergodic theorem along trees and its consequences

1st December – postponed to 15th December due to UCU strike action

25th November 2021 – Cancelled

17th November 2021
Speaker: Monica VanDieren, Robert Morris University
Title: Twenty Years of Tameness

10th November 2021
Speaker: Victoria Gitman, CUNY Graduate Center
Title: Set theory without powerset

3rd November 2021 (will be at 14:00-15:15 GMT)
Speaker: Katrin Tent, Westfälische Wilhelms-Universität Münster
Title: Simple automorphism groups

27th October 2021 (will be at 16:00-17:15 BST)
Speaker: Dilip Raghavan, National University of Singapore
Title: Galvin’s problem in higher dimensions

20th October 2021
Speaker: Mirna Džamonja, CNRS – Université de Paris
Title: On the universality problem for \aleph_2-Aronszajn and wide  \aleph_2 Aronszajn trees

13th October 2021
Speaker: Sam Adam-Day, University of Oxford
Title: Rigid branchwise-real tree orders

23rd June 2021
Speaker: Jinhe (Vincent) Ye, Institut de Mathématiques de Jussieu-Paris Rive Gauche
Title: The étale open topology and the stable fields conjecture

16th June 2021
Speaker: Sylvy Anscombe, Institut de Mathématiques de Jussieu-Paris Rive Gauche
Title: Some existential theories of fields
Slides

9th June 2021
Speaker: Vahagn Aslanyan, University of East Anglia
Title: A geometric approach to some systems of exponential equations

2nd June 2021
Speaker: Jing Zhang, Bar-Ilan University
Title: When does compactness imply guessing? 

26th May 2021 (will be at 16:45 BST)
Speaker: Nam Trang, University of California, Irvine
Title: Sealing of the Universally Baire sets
Slides

19th May 2021
Speaker: Dorottya Sziráki, Alfréd Rényi Institute of Mathematics
Title: The open dihypergraph dichotomy and the Hurewicz dichotomy for generalized Baire spaces

12th May 2021
Speaker: Ibrahim Mohammed, University of Leeds
Title: Hyperlogarithmic contraction groups

5th May 2021 (will be at 16:45 BST)
Speaker: Natasha Dobrinen, University of Denver
Title:  Ramsey theory on infinite structures
Corrected paper

28th April 2021 (will be at 14:45 UK time)
Speaker: Justine Falque, Université Paris-Sud
Title: Classification of oligomorphic groups with polynomial profiles, conjectures of Cameron and Macpherson.
Slides

24th March 2021
Speaker: Silvia Barbina, The Open University
Title: Model theory of Steiner triple systems

17th March 2021
Speaker: Sonia Navarro Flores, Universidad Nacional Autónoma de México
Title: Ramsey spaces and Borel ideals

10th March 2021
Speaker: Dana Bartošová, University of Florida
Title: Universal minimal flows of group extensions

3rd March 2021
Speaker: Marlene Koelbing, Universität Wien
Title: Distributivity spectrum of forcing notions
Slides

24th February 2021
Speaker: Erin Carmody, Fordham College
Title: The relationships between measurable and strongly compact cardinals. (Part 2)

17th February 2021
Speaker: Erin Carmody, Fordham College
Title: The relationships between measurable and strongly compact cardinals. (Part 1)

10th February 2021
Speaker: Adrian Mathias, Université de la Réunion
Title: Power-admissible sets and ill-founded omega-models
References

3rd February 2021
Speaker: Lynn Scow, California State University, San Bernardino
Title: Semi-retractions and preservation of the Ramsey property

27th January 2021
Speaker: Tin Lok (Lawrence) Wong, National University of Singapore
Title: Arithmetic under negated induction
Slides

20th January 2021
Speaker: Rehana Patel, African Institute for Mathematical Sciences Senegal
Title: Combining logic and probability in the presence of symmetry

13th January 2021
Speaker: Salma Kulhmann, University of Konstanz
Title: Strongly NIP almost real closed fields
Slides

16th December 2020
Speaker: Francesco Gallinaro
Title: Algebraic flows on tori: an application of model theory

9th December 2020
Speaker: Kaethe Minden, Bard College at Simon’s Rock
Title: Split Principles and Large Cardinals
Slides

2nd December 2020
Speaker: Ronnie Nagloo, Bronx Community College, City University of New York
Title: Geometric triviality in differentially closed fields
Slides

25th November 2020
Speaker: Rob Sullivan, Imperial College London
Title: Type spaces, Hrushovski constructions and giraffes

18th November 2020
Speaker: Vincenzo Mantova, University of Leeds
Title: Proving o-minimality of real exponentiation with restricted analytic functions (Part 2)
Slides

11th November 2020
Speaker: Laura Fontanella, Université Paris-Est Créteil
Title: Realizability and the Axiom of Choice
Slides

4th November 2020
Speaker: Vincenzo Mantova, University of Leeds
Title: Proving o-minimality of real exponentiation with restricted analytic functions (Part 1)
Slides

28th October 2020
Speaker: Zaniar Ghadernezhad, Imperial College London
Title: Building countable generic structures
Slides

21st October 2020
Speaker: Andrew Brooke-Taylor, University of Leeds
Title: An introduction to large cardinal axioms

14th October 2020
Speaker:  Dugald Macpherson, University of Leeds
Title:  Around stability theory (Part 2)

6th October 2020
Speaker:  Dugald Macpherson, University of Leeds
Title:  Around stability theory (Part 1)