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arXiv · 2206.12631

Type systems and maximal subgroups of Thompson's group $V$

James Belk·Collin Bleak·Martyn Quick·Rachel Skipper
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Abstract

We introduce the concept of a type system~$\Part$, that is, a partition on the set of finite words over the alphabet~$\{0,1\}$ compatible with the partial action of Thompson's group~$V$, and associate a subgroup~$\Stab{V}{\Part}$ of~$V$. We classify the finite simple type systems and show that the stabilizers of various simple type systems, including all finite simple type systems, are maximal subgroups of~$V$. We also find an uncountable family of pairwise non-isomorphic maximal subgroups of~$V$. These maximal subgroups occur as stabilizers of infinite simple type systems and have not been described in previous literature: specifically, they do not arise as stabilizers in $V$ of finite sets of points in Cantor space. Finally, we show that two natural conditions on subgroups of $V$ (both related to primitivity) are each satisfied only by $V$ itself, giving new ways to recognise when a subgroup of $V$ is not actually proper.

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James Belk, Collin Bleak, Martyn Quick, Rachel Skipper. 2024-02-26. Type systems and maximal subgroups of Thompson's group $V$. https://arxiv.org/abs/2206.12631

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