Topological matchings and amenability

Abstract

We establish a characterization of amenability for general Hausdor topological groups in terms of matchings with respect to finite uniform coverings. Furthermore, we prove that it suffices to just consider two-element uniform coverings. We also show that extremely amenable as well as compactly approximable topological groups satisfy a perfect matching property condition-the latter even with regard to arbitrary (i.e., possibly infinite) uniform coverings. Finally, we prove that the automorphism group of a Fraisse limit of a metric Fraisse class is amenable if and only if the class has a certain Ramsey-type matching property.