Definition 6

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

General Topology, chapter I, § 1. Open sets, neighbourhoods, closed sets

A base of the topology of a topological space $X$ is any set $\mathfrak{B}$ of open subsets of $X$ such that every open subset of $X$ is the union of sets belonging to $\mathfrak{B}$ .

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

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Cites

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