It is well known that in a stable theory, all types are definable. In an unstable context, we can ask (like Cubides and Delon in [CD]) over which models $M$ of a given theory all types are definable. These models are exactly the models which are…
Categoria evento: Logic Seminar
Matroid endomorphisms, derivatives, and Kolchin polynomials – Antongiulio Fornasiero (Università degli Studi di Firenze)
Let d be a finite tuple of commuting derivations on a field K. A classical result allows us to associate a numerical polynomial to d (the Kolchin polynomial), measuring the “growth rate” of d. A multi-variate version of the same polynomial is also…
Dinamica topologica e misure sullo spazio degli ultrafiltri – Moreno Pierobon (Università di Pisa)
L’utilizzo degli ultrafiltri su $\mathbb N$ per descrivere le proprietà di ricorrenza in dinamica topologica è un tema di ricerca ben studiato (tra gli altri, da Bergelson, Blass, Hindman e Strauss). In particolare, lo spazio $\beta\mathbb N$ degli…
Automorfismi di gruppi abeliani ordinati e logica positiva – Rosario Mennuni (Università di Pisa)
Una costruzione comune in teoria dei modelli consiste nel partire da una teoria T, aggiungere al linguaggio un simbolo per un automorfismo, ottenendo una teoria T’, e considerare la classe K dei modelli esistenzialmente chiusi di T’. A volte, la…
Classification of imaginaries in existentially closed valued difference fields – Martin Hils (WWU Münster)
In their seminal work, Haskell, Hrushovski and Macpherson gave a classification of imaginaries (i.e. quotient objects in the definable category) in an algebraically closed valued field K by the so-called geometric sorts, namely the valued field sort…
L’ordine di Rudin-Keisler e ultrafiltri Tukey-massimali su algebre di Boole – Francesco Parente (Università degli Studi di Torino)
In questo seminario, presenterò alcuni risultati ottenuti in collaborazione con Jörg Brendle. Nella prima parte, introdurrò il concetto di Tukey-riducibilità, discutendo in particolare l’esistenza di ultrafiltri non massimali. Nella seconda parte,…
Asymptotic Combinatorics, Stability and Ultrafilters – EVENTO ANNULLATO – Amador Martin-Pizzarro (Albert-Ludwigs-Universität Freiburg)
A finite subset A of a group G is said to have doubling K if the set A\cdot A consisting of products a\cdot b, with a and b in A has size at most KA. Extreme examples of sets with small doubling are cosets of subgroups. Theorems of Freiman-Ruzsa…
(Cancellato) Characterizing o-minimal groups in tame expansions of o-minimal structures – Panteleimon Eleftheriou (University of Konstanz)
Il seminario è stato cancellato. Sarà riprogrammato in altra data. Alessandro Berarducci P. Eleftheriou, “Characterizing o-minimal groups in tame expansions of o-minimal structures”, Journal of the Institute of Mathematics of Jussieu, Online first…
Generic derivations on o-minimal structures – Antongiulio Fornasiero (Università di Firenze)
Generic derivations on o-minimal structures Given an o-minimal theory, we define what is a derivation “compatible” with T. We show that the theory of compatible derivations has a model completion, and describe some of its properties.…
Definably amenable NIP groups – Pierre Simon (CNRS, Université Lyon)
A group is definably amenable if there is a translation-invariant measure on the algebra of definable sets. This notion is particularly fruitful in the NIP context, where definable amenability is equivalent to the existence of some kind of generic…