On Thompson Groups for Ważewski Dendrites

Abstract

We study a family of Thompson-like groups built as rearrangement groups of fractals from [BF19], each acting on a Ważewski dendrite. Each of these is a finitely generated group that is dense in the full group of homeomorphisms of the dendrite (studied in [DM19]) and has infinite-index finitely generated simple commutator subgroup, with a single possible exception. More properties are discussed, including finite subgroups, the conjugacy problem, invariable generation and existence of free subgroups. We discuss many possible generalizations, among which we find the Airplane rearrangement group $T_A$. Despite close connections with Thompson's group $F$, dendrite rearrangement groups seem to share many features with Thompson's group $V$.

Version 3 is the final version, closely resembling the accepted version (in particular, the numeration of statements, figures, etc is the same). Some discussions and proofs were cleaned and streamlined, resulting in the removal of any mention of the "permutation subgroups" (except for "central one") from the previous version