model theory 1permutation groups 1sharp transitivity 1ultrahomogeneous structures 1virtually free groups 1
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math.LO2025
Group-extensive embeddings into Fraïssé structures and stationary weak independence relations
Aleksandra Kwiatkowska, Rob Sullivan, Jeroen Winkel
Let be a Fraïssé structure (a countably infinite ultrahomogeneous structure). We call an embedding 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 Fraïssé 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
The externally definable Ramsey property and fixed points on type spaces
Nadav Meir, Rob Sullivan
We discuss the externally definable Ramsey property, a weakening of the Ramsey property for ultrahomogeneous structures, where the only colourings considered are those that are ext…