Bourbaki

Example 1

Tag 0237, permanent. Cite it as [Bourbaki, Tag 0237].

Topologie algébrique, chapter IV, § 5. Théorème de van Kampen

For the case of a covering formed of two sets, see No. 3.

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-5-6, 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.