Bourbaki

Corollary 2

Tag 0D0G, permanent. Cite it as [Bourbaki, Tag 0D0G].

Commutative Algebra, chapter X, § 1. Profondeur

Let A be a local ring, J an ideal of finite type of A distinct from A, M a nonzero A-module of finite type. Put r=[J/mAJ:κA]r = [J/m_AJ : \kappa_A]. One has prof⁡A(J;M)≤r\operatorname{prof}_A(J; M) \leq r ; there is equality if and only if J is generated by a family completely secant for M. In this case, in order that a generating family of J be completely secant, it is necessary and sufficient that it have r elements.

By Nakayama's lemma, one has JM≠MJM \neq M, and r is the minimal number of generators of J; Corollary 2 therefore follows from Corollary 1.

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

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