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The planar 3-colorable subgroup ε of Thompson’s group F and its even part

Published online by Cambridge University Press:  25 November 2024

Valeriano Aiello*
Affiliation:
Dipartimento di Matematica, Università di Roma La Sapienza, Roma, Italy
Tatiana Nagnibeda
Affiliation:
Section de Mathématiques, Université de Genève, Genève, Switzerland
*
Corresponding author: Valeriano Aiello, email: valerianoaiello@gmail.com

Abstract

We study the planar 3-colorablesubgroup $\mathcal{E}$ of Thompson’s group F and its even part ${\mathcal{E}_{\rm EVEN}}$. The latter is obtained by cutting $\mathcal{E}$ with a finite index subgroup of F isomorphic to F, namely the rectangular subgroup $K_{(2,2)}$. We show that the even part ${\mathcal{E}_{\rm EVEN}}$ of the planar 3-colorable subgroup admits a description in terms of stabilisers of suitable subsets of dyadic rationals. As a consequence ${\mathcal{E}_{\rm EVEN}}$ is closed in the sense of Golan and Sapir. We then study three quasi-regular representations associated with ${\mathcal{E}_{\rm EVEN}}$: two are shown to be irreducible and one to be reducible.

Information

Type
Research Article
Copyright
© The Author(s), 2024. Published by Cambridge University Press on Behalf of The Edinburgh Mathematical Society.

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