Equivariant embedding of finite-dimensional dynamical systems

Abstract

We prove an equivariant version of the classical Menger-Nobeling theorem regarding topological embeddings: Whenever a group $G$ acts on a finite-dimensional compact metric space $X$, a generic continuous equivariant function from $X$ into $([0,1]^r)^G$ is a topological embedding, provided that for every positive integer $N$ the space of points in $X$ with orbit size at most $N$ has topological dimension strictly less than $\frac{rN}{2}$. We emphasize that the result imposes no restrictions whatsoever on the acting group $G$ (beyond the existence of an action on a finite-dimensional space). Moreover, if $G$ is finitely generated then there exists a finite subset $F\subset G$ so that for a generic continuous map $h:X\to [0,1]^{r}$, the map $h^{F}:X\to ([0,1]^{r})^{F}$ given by $x\mapsto (f(gx))_{g\in F}$ is an embedding. This constitutes a generalization of the Takens delay embedding theorem into the topological category.