Bourbaki

Example 2

Tag 022X, permanent. Cite it as [Bourbaki, Tag 022X].

Topologie algébrique, chapter IV, § 4. Théorie de la descente

It also applies when the space X is the sum space of a family (Vi)i∈I(V_i)_{i\in I} of parts of Y whose interiors cover Y, and when ff is the mapping induced by the canonical injections of each of the ViV_i into Y.

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.

Cited by

Nothing.

Cites

Nothing.

Machine translation of the English, by gpt-5-6-mini, gpt-5.4, against glossary version 34. Not checked by a person. That model is a cut down version of the one the rest of this language was written by.