Bourbaki

Corollary

Tag 0CN0, permanent. Cite it as [Bourbaki, Tag 0CN0].

Commutative Algebra, chapter VIII, § 3. Dimension des anneaux noethériens

Every sequence of elements of mAm_A which is completely secant for M (A, X, p. 157, Definition 2) is secant for M. Let (x1,...,xr)(x_1, ..., x_r) be a sequence of elements of mAm_A which is completely secant for M. Put M0=MM_0 = M and by induction Mi=Mi−1/xiMi−1M_i = M_{i-1}/x_i M_{i-1} for 1≤i≤r1 \leq i \leq r. By Corollary 1 of A, X, p. 160, the homothety of ratio xix_i in Mi−1M_{i-1} is injective, whence dim⁡A(Mi)=dim⁡A(Mi−1)−1\dim_A(M_i) = \dim_A(M_{i-1}) - 1 (for 1≤i≤r1 \leq i \leq r) (Proposition 3). Therefore one has

dim⁡A(M)=r+dim⁡A(M/(x1M+⋯+xrM)), \dim_A(M) = r + \dim_A(M/(x_1M + \cdots + x_rM)) ,
hence the sequence (x1,...,xr)(x_1, ..., x_r) is secant for M.

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

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