Bourbaki

Proposition 8

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

Algebra, chapter X, § 4. Produits de torsion

Let I (resp. J) be a right filtered preordered set, ((MαM_\alpha, uα′,αu_{\alpha', \alpha}) (resp. ((NβN_\beta, vβ′,βv_{\beta', \beta}))) an inductive system of right A-modules (resp. left) relative to I (resp. J). The homomorphism of graded k-modules

lim⁡⟶(α,β)∈I×JTorA(Mα,Nβ)→TorA(lim⁡⟶α∈IMα,lim⁡⟶β∈JNβ), \lim_{\longrightarrow (\alpha, \beta) \in I \times J} \mathrm{Tor}^A(M_\alpha, N_\beta) \to \mathrm{Tor}^A\left( \lim_{\longrightarrow \alpha \in I} M_\alpha, \lim_{\longrightarrow \beta \in J} N_\beta \right),

deduced from the canonical A-homomorphisms Mα→lim⁡⟶MαM_\alpha \to \lim_{\longrightarrow} M_\alpha and Nβ→lim⁡⟶NβN_\beta \to \lim_{\longrightarrow} N_\beta, is bijective.

In particular, taking J=IJ = I and remarking that the (α,α),α∈I(\alpha, \alpha), \alpha \in I, form a cofinal subset of I×II \times I, one obtains :

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

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Translated with machine help, not yet reviewed by a person.