Bourbaki

Lemma 2

Tag 04G5, permanent. Cite it as [Bourbaki, Tag 04G5].

Commutative Algebra, chapter III, § 3. m-adic topologies on Noetherian rings

Let A,BA, B be two commutative Noetherian rings, ϕ:A→B\phi : A \to B a ring homomorphism, EE a finitely generated AA-module and FF a finitely generated BB-module. Then HomA(E,ϕ∗(F))\mathrm{Hom}_A(E, \phi_*(F)) is a finitely generated BB-module.

There exists by hypothesis a surjective AA-homomorphism v:An→Ev : A^n \to E; the mapping u↦u∘vu \mapsto u \circ v of HomA(E,ϕ∗(F))\mathrm{Hom}_A(E, \phi_*(F)) to HomA(An,ϕ∗(F))\mathrm{Hom}_A(A^n, \phi_*(F)) is therefore injective and, as BB is Noetherian, it is sufficient to prove that HomA(An,ϕ∗(F))\mathrm{Hom}_A(A^n, \phi_*(F)) is a finitely generated BB-module; which is immediate since it is isomorphic to FnF^n.

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

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Cites

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Transcribed from the printed volume. Not translated.