Bergelson's amenability conjecture via recurrence

Let GG be a group. A set RGR\subset G is a set of measurable recurrence if, for every measure-preserving GG-system (X,X,μ,(Tg))(X,\mathcal{X},\mu,(T_g)) and every AXA\in\mathcal{X} with μ(A)>0\mu(A)>0, there exists gRg\in R^{*} such that

μ(ATg1A)>0.\mu(A\cap T_g^{-1}A)>0.

A set RGR\subset G is a set of topological recurrence if it has the corresponding recurrence property for topological GG-systems. The Bergelson amenability conjecture. The group GG is amenable if and only if every set of measurable recurrence RGR\subset G is a set of topological recurrence.

This conjecture proposes a characterization of amenability through the equivalence of measurable and topological recurrence. The source notes that the implication from topological to measurable recurrence can fail in general, while amenable groups satisfy the forward implication; the converse characterization is presented as open.

Sources & referencesView supporting material

Primary source

Ioannis Kousek and Vicente Saavedra-Araya, “Uniqueness of a topological Furstenberg system”, arXiv:2603.27899 (2026).

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