Compactifications of the homeomorphism group of a graph

Let Γ be a countable locally finite graph and let H(Γ) and H+(Γ) denote the homeomorphism group of Γ with the compact-open topology and its identity component. These groups can be embedded into the space of all closed sets of Γ×Γ with the Fell topology, which is compact. Taking closure, we have natural compactifications and . In this paper, we completely determine the topological type of the pair and give a necessary and sufficient condition for this pair to be a (Q,s)-manifold. The pair is also considered for simple examples, and in particular, we find that has homotopy type of RP3. In this investigation we point out a certain inaccuracy in Sakai–Uehara's preceding results on for finite graphs Γ.