Jeroen Winkel

activity

20242026

collaborators

6 papers

math.LO2026

An unusual example of a universal automorphism group

Rob Sullivan, Jeroen Winkel

Let $M$ be a FraÃ¯ssÃ© structure (a countably infinite ultrahomogeneous structure). We refer to the class of structures embeddable in $M$ as the $I ¨ $ -age of $M$ . We consider the fo…

math.LO2026

Determining the normal subgroups of the automorphism groups of ultrahomogeneous structures via stabilisers

Thomas Bernert, Rob Sullivan, Jeroen Winkel +1

We show the simplicity of the automorphism groups of the generic $n$ -hypertournament and the semigeneric tournament, and determine the normal subgroups of the automorphism groups o…

math.CO2026

Structured sunflowers and canonical Ramsey properties

Rob Sullivan, Jeroen Winkel

A first-order structure $M$ is said to have the infinite sunflower property if, for each $k \in N_{+}$ and each structure $M^{'} ≅ M$ whose elements are $k$ -sets, there is…

math.LO2025

Group-extensive embeddings into Fraïssé structures and stationary weak independence relations

Aleksandra Kwiatkowska, Rob Sullivan, Jeroen Winkel

Let $M$ be a Fraïssé structure (a countably infinite ultrahomogeneous structure). We call an embedding $f : A \to M$ group-extensive if each automorphism of its image extends to an…

math.LO2025

Embeddings into the generic poset

Aleksandra Kwiatkowska, Rob Sullivan, Jeroen Winkel

Let M be the generic poset, defined as the FraÃ¯ssÃ© limit of the class of finite posets. We show that every countably infinite poset A can be embedded with coinfinite image into M…

math.LO2024

Infinite Hat Problems and Large Cardinals

Andreas Lietz, Jeroen Winkel

Picture countably many logicians all wearing a hat in one of $I^º$ -many colours. They each get to look at finitely many other hats and afterwards make finitely many guesses for thei…