A dynamical definition of f.g. virtually free groups

Daniel Bennett, Collin Bleak

Research output: Contribution to journalArticlepeer-review

Abstract

We show that the class of finitely generated virtually free groups is precisely the class of demonstrable subgroups for R. Thompson's group V. The class of demonstrable groups for V consists of all groups which can embed into V with a natural dynamical behaviour in their induced actions on the Cantor space C2 := {0,1}ω. There are also connections with formal language theory, as the class of groups with context-free word problem is also the class of finitely generated
virtually free groups, while R. Thompson's group V is a candidate as a
universal coCF group by Lehnert's conjecture, corresponding to the class of
groups with context free co-word problem (as introduced by Holt, Rees, Röver, and Thomas). Our main results answers a question of Berns-Zieze, Fry, Gillings, Hoganson, and Matthews, and separately of Bleak and Salazar-Días, and fits into the larger exploration of the class of coCF groups as it shows that all four of the known properties of the class of coCF groups hold for the set of finitely generation subgroups of V.
Original languageEnglish
Pages (from-to)105-121
Number of pages17
JournalInternational Journal of Algebra and Computation
Volume26
Issue number1
Early online date22 Jan 2016
DOIs
Publication statusPublished - Feb 2016

Keywords

  • CoCF groups
  • Thompson Groups
  • Lehnert's Conjecture
  • Group actions
  • Geometric actions

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