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arXiv · 2609.30158

A finitely generated ICC non property (T) group that is neither inner amenable nor properly proximal

Xin Ma
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Abstract

This note record a finitely generated extension of Caprace's example of a non-inner-amenable group is also not properly proximal, which answers the original question by Boutonnet, Ioana and Peterson. The extension is an explicit ICC subgroup of $\operatorname{GL}_4(\mathbb{F}_2(t))$, which has no property \textup{(T)}. Failure of proper proximality follows from the work of Ishan-Peterson-Ruth and the passage of proper proximality to co-amenable subgroups. Non-inner-amenability follows from a property-\textup{(T)} subgroup and an elementary centralizer computation.

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Xin Ma. 2026-09-24. A finitely generated ICC non property (T) group that is neither inner amenable nor properly proximal. https://arxiv.org/abs/2609.30158

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