English

Some isomorphism results for Thompson like groups $V_n(G)$

Group Theory 2014-12-18 v2 Dynamical Systems

Abstract

We consider a class of groups Vn(G)V_n(G) which are supergroups of the Higman-Thompson groups VnV_n. These groups fit in a framework of Elizabeth Scott for generating infinite virtually simple groups, and the groups we study in particular are initially introduced by Farley and Hughes. The group Vn(G)V_n(G) is the result one obtains by taking the VnV_n generators and adding a tree automorphism for each generator of a subgroup GG of the symmetric group on nn letters, where the new generators each permute the child leaves of a specific vertex α\alpha of the infinite rooted nn-ary tree according to the permutation they represent, and then they iterate this permutation again at each vertex which is a descendent of α\alpha. Farley and Hughes show that Vn(G)V_n(G) is not isomorphic to VnV_n when GG fails to act freely on the points {1,2,...,n}\{1,2,...,n\}, and expect further non-isomorphism results in the other cases. We show the perhaps surprising result that if GG does act freely, then Vn(G)VnV_n(G)\cong V_n. We also generalise these results and produce some examples of even more isomorphisms amongst groups in the family Vn(G)V_n(G). Essential tools in the above work are a study of the dynamics of the action of elements of Vn(G)V_n(G) on Cantor space, Rubin's Theorem, and transducers from Grigorchuk, Nekrashevych, and Suschanski\u{i}'s rational group on the nn-ary alphabet.

Keywords

Cite

@article{arxiv.1410.8726,
  title  = {Some isomorphism results for Thompson like groups $V_n(G)$},
  author = {Collin Bleak and Casey Donoven and Julius Jonušas},
  journal= {arXiv preprint arXiv:1410.8726},
  year   = {2014}
}

Comments

10 pages and 3 figures; updated to clean text

R2 v1 2026-06-22T06:43:20.457Z