Proposition 4

Tag 058V, permanent. Cite it as [Bourbaki, Tag 058V].

Let H and K be two subgroups of a group G such that H $\subset$ K. Then

(G:H) = (G:K)(K:H).

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

Cited by

Nothing.