Bourbaki

Corollary

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

Commutative Algebra, chapter VIII, § 4. Séries de Hilbert-Samuel

Let AA be a noetherian ring, MM a finitely generated AA-module and qq an ideal of AA such that M/qMM/qM is of finite length. Then dq(M)d_q(M) is the least upper bound of the dimensions dim⁡Am(Mm)\dim_{A_m}(M_m), where mm ranges over the finite set S=Supp⁡(M)∩V(q)S = \operatorname{Supp}(M) \cap V(q), and eq(M)e_q(M) is the sum of the eqm(Mm)e_{q_m}(M_m) extended to those elements mm of SS for which one has dim⁡Am(Mm)=dq(M)\dim_{A_m}(M_m) = d_q(M).

For each integer nn, the length of M/qnMM/q^nM is the sum of the long⁡Am(Mm/qmnMm)\operatorname{long}_{A_m}(M_m/q^n_m M_m) (IV, §2§ 2, No. 5, cor. 1 to prop. 7 and corollary to prop. 8). Consequently, one has HM,q=∑m∈SHMm,qmH_{M,q} = \sum_{m \in S} H_{M_m,q_m}, whence the corollary.

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

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