English

On the isometrization of groups of homeomorphisms

General Topology 2021-05-19 v1 Group Theory Geometric Topology Metric Geometry

Abstract

Let GG be a group of homeomorphisms of a topological space XX. GG is (properly) isometrizable\textit{(properly) isometrizable} if there exists a GG-invariant (proper) gauge structure on XX. GG is equiregular\textit{equiregular} if for every xXx \in X and every open neighborhood UU of xx in XX there is an open neighborhood VV of xx in XX such that cl(V)Ucl(V) \subset U and every yXy \in X has an open neighborhood NyN_y with the property that for every gGg \in G, if g(Ny)cl(V)g(N_y) \cap cl(V) \neq \emptyset, then g(Ny)Ug(N_y) \subset U. GG is nearly proper\textit{nearly proper} if for all compact subsets AA and BB of XX, clcl ( \bigcup { g(A):gGg(A):g\in G and g(A)Bg(A)\cap B \neq \emptyset } ) is compact. GG acts properly on\textit{acts properly on} XX if for all compact subsets AA and BB of XX, the subset GA,BG_{A,B} = { gG:g(A)Bg\in G : g(A) \cap B \neq \emptyset } is compact when GG is endowed with the compact-open topology. THE ISOMETRIZATION THEOREM: If XX is a Hausdorff space and GG \ XX is a paracompact regular space, then: GG is isometrizable if and only if GG is equiregular. THE PROPER ISOMETRIZATION THEOREM: If XX is a locally compact σ\sigma-compact Hausdorff space and GG \ XX is a regular space, then: GG is properly isometrizable if and only if GG is equiregular and nearly proper. The PROPER ISOMETRIZATION THEOREM has the following corollary. THEOREM OF ABEL-MANOUSSOS-NOSKOV: If XX is a locally compact σ\sigma-compact Hausdorff space and GG acts properly on XX, then XX is properly isometrizable.

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Cite

@article{arxiv.2105.08218,
  title  = {On the isometrization of groups of homeomorphisms},
  author = {Fredric D. Ancel},
  journal= {arXiv preprint arXiv:2105.08218},
  year   = {2021}
}