Amenability, connected components, and definable actions

E Hrushovski, K Krupiński, A Pillay - Selecta Mathematica, 2022 - Springer
We study amenability of definable groups and topological groups, and prove various results,
briefly described below. Among our main technical tools, of interest in its own right, is an …

When invariance implies exchangeability (and applications to invariant Keisler measures)

S Braunfeld, C Jahel, P Marimon - arXiv preprint arXiv:2408.08370, 2024 - arxiv.org
We study the problem of when, given a homogeneous structure $ M $ and a space $ S $ of
expansions of $ M $, every $\mathrm {Aut}(M) $-invariant probability measure on $ S $ is …

Some model theory and topological dynamics of p-adic algebraic groups

D Penazzi, A Pillay, N Yao - arXiv preprint arXiv:1704.07764, 2017 - arxiv.org
We initiate the study of p-adic algebraic groups G from the stability-theoretic and definable
topological-dynamical points of view, that is, we consider invariants of the action of G on its …

On first order amenability

E Hrushovski, K Krupiński, A Pillay - arXiv preprint arXiv:2004.08306, 2020 - arxiv.org
We introduce the notion of first order amenability, as a property of a first order theory $ T $:
every complete type over $\emptyset $, in possibly infinitely many variables, extends to an …

Boundedness and absoluteness of some dynamical invariants in model theory

K Krupiński, L Newelski, P Simon - Journal of Mathematical Logic, 2019 - World Scientific
Let ℭ be a monster model of an arbitrary theory T, let α ̄ be any (possibly infinite) tuple of
bounded length of elements of ℭ, and let c ̄ be an enumeration of all elements of ℭ (so a …

Twenty years of Ne\v {s} et\v {r} il's classification programme of Ramsey classes

J Hubička, M Konečný - arXiv preprint arXiv:2501.17293, 2025 - arxiv.org
In the 1970s, structural Ramsey theory emerged as a new branch of combinatorics. This
development came with the isolation of the concepts of the $\mathbf {A} $-Ramsey property …

On Model-Theoretic Connected Groups

J Gismatullin - The Journal of Symbolic Logic, 2024 - cambridge.org
We introduce and study the model-theoretic notions of absolute connectedness and type-
absolute connectedness for groups. We prove that groups of rational points of split …

On n-dependent groups and fields III. Multilinear forms and invariant connected components

A Chernikov, N Hempel - arXiv preprint arXiv:2412.19921, 2024 - arxiv.org
We develop some model theory of multi-linear forms, generalizing Granger in the bi-linear
case. In particular, after proving a quantifier elimination result, we show that for an NIP field …

On finite sets of small tripling or small alternation in arbitrary groups

G Conant - Combinatorics, Probability and Computing, 2020 - cambridge.org
We prove Bogolyubov–Ruzsa-type results for finite subsets of groups with small tripling,|
A3|≤ O (| A|), or small alternation,| AA− 1A|≤ O (| A|). As applications, we obtain a …

Bohr compactifications of groups and rings

J Gismatullin, G Jagiella, K Krupiński - The Journal of Symbolic Logic, 2023 - cambridge.org
We introduce and study model-theoretic connected components of rings as an analogue of
model-theoretic connected components of definable groups. We develop their basic theory …