Remark 4

Tag 01Z0, permanent. Cite it as [Bourbaki, Tag 01Z0].

Topologie algébrique, chapter III, § 3. Groupoïde de Poincaré

The proposition and its corollary apply in particular when $(A_i)_{i\in I}$ is an increasing family of subsets of X indexed by a directed ordered set I such that the interiors of the $A_i$ cover X.

Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.

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Cites

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