Definition 2
Tag 01QK, permanent. Cite it as [Bourbaki, Tag 01QK].
Topologie algébrique, chapter I, § 5. Revêtements principaux
Let B be a topological space and let G be a group. Endow G with the discrete topology. A principal fibre space with base B and group G is called a principal covering of B with group G.
This terminology is legitimate, for such a B-space is a covering of B.
A principal covering with group G of a nonempty topological space possesses a degree, equal to Card G.
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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