Bourbaki

Remark (2)

Tag 053P, permanent. Cite it as [Bourbaki, Tag 053P].

Commutative Algebra, chapter VII, § 4. Modules over integrally closed Noetherian domains

In the statement of Theorem 5, the modules A/piniA/p_i^{n_i} may be replaced by A/pi(ni)A/p_i^{(n_i)} (§1§ 1, no. 4, Proposition 8). For all p∈Pp \in P, the canonical mapping g:A/pn→A/p(n)=A/(A∩pnAp)g : A/p^n \to A/p^{(n)} = A/(A \cap p^nA_p) is a pseudo-isomorphism, as, for all q∈Pq \in P distinct from pp, Aq/pnAq=Aq/p(n)Aq=0A_q/p^nA_q = A_q/p^{(n)}A_q = 0 and Ap/pnAp=Ap/p(n)ApA_p/p^nA_p = A_p/p^{(n)}A_p.

\* Given an exact sequence of AA-modules, E→F→GE \to F \to G, if EE and GG are pseudo-zero, so is FF, as follows from Definition 2 and Chapter II, §2, no. 4, Theorem 1. In the language of categories, we may then say that, in the category C\mathscr{C} of AA-modules, the sub-category C′\mathscr{C}' of pseudo-zero modules is full and we may then define the quotient category C/C′\mathscr{C}/\mathscr{C}': the objects in this category are also AA-modules but the set of morphisms from EE to FF (for E,FE, F in C/C′\mathscr{C}/\mathscr{C}') is the direct limit of the set of commutative groups HomA(E′,F′)\mathrm{Hom}_A(E', F'), where E′E' (resp. F′F') runs through the set of submodules of EE (resp. the set of quotient modules F/F′′F/F'' of FF) such that E/E′E/E' (resp. F′′F'') is pseudo-zero. Of course, for every ordered pair of AA-modules E,FE, F, there is a canonical homomorphism HomE(E,F)→HomE/E′(E,F)\mathrm{Hom}_{\mathscr{E}}(E, F) \to \mathrm{Hom}_{\mathscr{E}/\mathscr{E}'}(E, F). To say that a homomorphism u∈HomA(E,F)u \in \mathrm{Hom}_A(E, F) is pseudo-zero (resp. pseudo-injective, pseudo-surjective, pseudo-bijective) means that its canonical image in HomE/E′(E,F)\mathrm{Hom}_{\mathscr{E}/\mathscr{E}'}(E, F) is zero (resp. a monomorphism, an epimorphism, an isomorphism). \*

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.