Bourbaki

Proposition 11

Tag 048G, permanent. Cite it as [Bourbaki, Tag 048G].

Commutative Algebra, chapter II, § 3. Local rings. Passage from the local to the global

Let M be an A-module, N a finitely generated A-module and u:M→Nu : M \to N a homomorphism. For u to be surjective, it is necessary and sufficient that, for all m∈S2m \in S_2, the homomorphism M/mM→N/mNM/mM \to N/mN derived from uu by taking quotients be surjective.

It follows from Theorem 1 that, for uu to be surjective, it is necessary and sufficient that um:Mm→Nmu_m : M_m \to N_m be surjective for all m∈Ωm \in \Omega. As AA is a local ring and NmN_m is a finitely generated AmA_m-module, this amounts to saying that the homomorphism um′:Mm/mMm→Nm/mNmu'_m : M_m/mM_m \to N_m/mN_m, obtained by taking quotients, is surjective (no. 2, Corollary 1 to Proposition 4); but Mm/mMmM_m/mM_m (resp. Nm/mNmN_m/mN_m) is identified with M/mMM/mM (resp. N/mNN/mN) (Proposition9), whence the proposition.

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

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Transcribed from the printed volume. Not translated.