Bourbaki

Exercise 31, § 4

General Topology, IX, p. 109

a) Let XX be a paracompact space, RR a closed equivalence relation in XX, such that every equivalence class under RR is compact. Prove that X/RX/R is paracompact. (It is known that X/RX/R is normal (IX, p. 105, exerc. 19). Use then IX, p. 107, exerc. 25 c)).¹ b) Let XX be a separated space, RR a closed equivalence relation in XX, such that every equivalence class under RR is compact. Prove that if X/RX/R is paracompact, XX is paracompact (reason as in I, p. 70, prop. 17). c) Let YY be a locally compact non-paracompact space (I, p. 106, exerc. 12), Y0Y_0 the compact space obtained by adjoining to YY a point at infinity. Let XX be the topological sum space of YY and Y0Y_0, RR the equivalence relation identifying every point of YY with its canonical image in Y0Y_0; the relation RR is open, every equivalence class under RR contains at most two points, and X/RX/R is homeomorphic to Y0Y_0, hence compact.

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Machine translation of the English, by gpt-5-mini. Not checked by a person. That model is a cut down version of the one the rest of this language was written by.