Lemma 10.39.7. Suppose that M is (faithfully) flat over R, and that R \to R' is a ring map. Then M \otimes _ R R' is (faithfully) flat over R'.
Proof. For any R'-module N we have a canonical isomorphism N \otimes _{R'} (R'\otimes _ R M) = N \otimes _ R M. Hence the desired exactness properties of the functor -\otimes _{R'}(R'\otimes _ R M) follow from the corresponding exactness properties of the functor -\otimes _ R M. \square
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