Geometry & Dynamics Seminar

Monday, 3.5.2004, 16-17:30, Schreiber bldg., room 210.




Matatyahu Rubin, Ben Gurion University

How to Reconstruct a Topological Space from a Group of Homeomorphisms of the Space


Abstract
                         
The following general question will be considered. Suppose that $X$ and $Y$ are topological spaces, $G$ is a subgroup of the group $H(X)$ of auto-homeomorphisms of $X$ and $H$ is a subgroup of $H(Y)$. Suppose further that $\phi$ is a group isomorphism between $G$ and $H$. Is there a homeomorphism $\tau$ between $X$ and $Y$ such that
      
       $\phi(g) = \tau o g o \tau^{-1}$ for every $g \in G$?

The answer to the above question is positive in several natural situations. For example, the above is true when X and Y are open subsets of normed spaces, $G$ contains the group $LIP^L(X)$ of locally bilipschitz homeomorphisms of $X$ and $H$ contains $LIP^L(Y)$.

For metric spaces $X$ we consider some specific subgroups of $H(X)$.
For example, let $LIP(X)$ be the group consisting of all bilipschitz homeomorphisms of $X$. We now ask whether the following statement is true.

If $\phi$ is an isomorphism between the groups $LIP(X)$ and $LIP(Y)$, then there is a bilipschitz homeomorphism $\tau$ between $X$ and $Y$ such that $\tau$ induces $\phi$.

This statement is true for bounded open subsets of a Banach space that have a "nice" boundary. Another setting in which a statement similar to the above is true is for spaces which are open subsets of the Uryson universal metric space.