Expansive maps of the circle
by Chris Connell, Steven Hurder, and Alex Furman

ABSTRACT:

Let G be a finitely-generated group, and $S^1$ the circle of radius 1. We let $\varphi \colon \G \times S^1 \rightarrow S^1$ denote an action of $\G$ on the circle by homeomorphisms. In this paper we answer a question posed by Thom Ward:

If $\varphi$ is an expansive action, then G cannot be an infra-nilpotent group.