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arXiv · 2506.02319

Finiteness properties of stabilisers of oligomorphic actions

Francesco Fournier-Facio·Peter H. Kropholler·Robert Alonzo Lyman·Matthew C. B. Zaremsky
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Abstract

An action of a group on a set is oligomorphic if it has finitely many orbits of $n$-element subsets for all $n$. We prove that for a large class of groups (including all groups of finite virtual cohomological dimension and all countable linear groups), for any oligomorphic action of such a group on an infinite set there exists a finite subset whose stabiliser is not of type $\mathrm{FP}_\infty$. This leads to obstructions on finiteness properties for permutational wreath products and twisted Brin-Thompson groups. We also prove a version for actions on flag complexes, and discuss connections to the Boone-Higman conjecture. In the appendix, we improve on the criterion of Bartholdi-Cornulier-Kochloukova for finiteness properties of wreath products, and the criterion of Kropholler-Martino for finiteness properties of graph-wreath products.

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Francesco Fournier-Facio, Peter H. Kropholler, Robert Alonzo Lyman, Matthew C. B. Zaremsky. 2026-02-27. Finiteness properties of stabilisers of oligomorphic actions. https://arxiv.org/abs/2506.02319

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