Bourbaki

Proposition 8

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

Algebra, chapter X, § 6. Utilisation de résolutions non canoniques

a) If NN is flat over AA and over BB, homomorphism (11) is bijective.

b) If NN is flat over AA and projective over BB, homomorphism (12) is bijective.

Indeed N⊗AL(Q)N \otimes_A L(Q) is isomorphic to a direct sum of copies of NN, hence is a flat (resp. projective) BB-module when the BB-module NN is flat (resp. projective); one then applies Theorem 1 (X, p. 100).

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

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