Bourbaki

Exercise 16, § 2

General Topology, X

Let XX be a Hausdorff uniform space and let Γ\Gamma be an equicontinuous group of homeomorphisms of XX. The equivalence relation RR defined by Γ\Gamma on XX is open (Chapter I, § 5, no. 2).

a) Show that if every orbit of Γ\Gamma is closed in XX, then the orbit space X/ΓX/\Gamma is Hausdorff.

b) Show that if every orbit of Γ\Gamma is compact, then the relation RR is closed (use Chapter I, § 5, no. 4, Proposition 10).

c) Give an example where XX is compact but none of the orbits of Γ\Gamma is closed in XX (cf. Chapter III, § 2, Exercise 29).

Solution

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