Bourbaki

Proposition 1

Tag 0B7Y, permanent. Cite it as [Bourbaki, Tag 0B7Y].

General Topology, chapter I, § 9. Compact spaces and locally compact spaces

Let X be a compact space, x a point of X. In order that a filter base B formed of closed neighbourhoods of x should be a fundamental system of neighbourhoods of x it is necessary and sufficient that the intersection of the sets of B consists of x alone.

The condition is necessary since X is Hausdorff (§ 8, no. 1, Proposition 1). It is sufficient, for it signifies that x is the only cluster point of B; hence B converges to x by the Corollary to Theorem 1 of no. 1.

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

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Transcribed from the printed volume. Not translated.