Bourbaki

Remark

Tag 0DU3, permanent. Cite it as [Bourbaki, Tag 0DU3].

Algebra, chapter X, § 3. Résolutions

If f,g∈HomA(M,N)f, g \in \mathrm{Hom}_A(M, N), one does not have I(f+g)=I(f)+I(g)I(f + g) = I(f) + I(g). However, these two morphisms are homotopic by X, p. 49, prop. 3 bis.

If M is a right A-module, one puts I(M)=I(M∘)∘I(M) = I(M^\circ)^\circ; this is called the canonical injective resolution of M, and one has

I(M∘)=I(M)∘. I(M^\circ) = I(M)^\circ .

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

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