Bourbaki

Proposition 7

Tag 0BGK, permanent. Cite it as [Bourbaki, Tag 0BGK].

General Topology, chapter II, § 4. Relations between uniform spaces and compact spaces

Let X be a compact space and let R be the equivalence relation on X whose classes are the components of X. Then the quotient space X/R is compact and totally disconnected.

We know from Chapter I, § II, no. 5, Proposition 9 that X/R is totally disconnected; hence we have to show that X/R is Hausdorff (Chapter I, § 10, no. 4, Proposition 8.) Let A and B be two distinct components of X. By Proposition 6 there is a symmetric entourage U of X such that no point of A can be joined to any point of B by a U-chain. The set V (resp. W) of points of X which can be joined to a point x ∈ A (resp. y ∈ B) by a U-chain is both open and closed in X (Proposition 5) and contains A (resp. B); these sets are therefore open neighbourhoods of A and B respectively, are saturated with respect to R and do not intersect. This completes the proof.

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

Cited by

Nothing.

Cites

Transcribed from the printed volume. Not translated.