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Homeomorphism spaces under uniform and fine topologies. (English) Zbl 1284.54032

Given a metric space \((X,d)\), the expression \(H(X)\) denotes the set of all homeomorphisms of \(X\) onto itself and \(H_d(X)\) stands for the set \(H(X)\) with the uniform topology generated by the metric \(d^*\) defined by the equality \(d^*(f,g)=\min\{1, \sup\{d(f(x),f(y)): x\in X\}\}\) for any \(f,g\in H(X)\). If \(W\) is an open subset of \(X\times X\) then \(G_W=\{g\in H(X): G(g)\subseteq W\}\); here \(G(g)=\{(x,g(x)): x\in X\}\) is the graph of the function \(g\). The topology on \(H(X)\) generated by all sets \(G_W\) is called the fine topology and the respective space is denoted by \(H_f(X)\).
The authors prove that for a locally homogeneous dense-in-itself metric space \(X\), the space \(H_f(X)\) is first countable if and only if \(H_f(X)\) is metrizable which in turn is equivalent to \(X\) being compact. They also consider three compatible metrics \(\rho, \sigma\) and \(\tau\) on the space \(\mathbb R^n\) for some natural number \(n\) and study the relationship between the topologies of the spaces \(H_\rho(\mathbb R^n)\), \(H_\sigma(\mathbb R^n)\) and \(H_\tau(\mathbb R^n)\).

MSC:

54C35 Function spaces in general topology
54A10 Several topologies on one set (change of topology, comparison of topologies, lattices of topologies)
54D05 Connected and locally connected spaces (general aspects)
54D65 Separability of topological spaces