Addendum to ``Commensurations and Subgroups of Finite Index of Thompson's Group $F$''

José Burillo, Sean Cleary, Claas Röver

Keywords

simple group,Thompson's group,commensurator

Abstract

It is shown that the abstract commensurator of $F$ is composed of four building blocks. Two isomorphism types of simple groups, the multiplicative group of the positive rationals and a cyclic group of order two. The main result establishes the simplicity of a certain group of piecewise linear homeomorphisms of the real line.

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