The Stacks project

Remark 15.84.19. The equivalences of Proposition 15.84.15, Theorem 15.84.17, and Proposition 15.84.18 preserve properties of modules. For example if $M$ corresponds to $\mathbf{M} = (M', M_ i, \alpha _ i, \alpha _{ij})$ then $M$ is finite, or finitely presented, or flat, or projective over $R$ if and only if $M'$ and $M_ i$ have the corresponding property over $S$ and $R_{f_ i}$. This follows from the fact that $R \to S \times \prod R_{f_ i}$ is faithfully flat and descend and ascent of these properties along faithfully flat maps, see Algebra, Lemma 10.82.2 and Theorem 10.94.5. These functors also preserve the $\otimes $-structures on either side. Thus, it defines equivalences of various categories built out of the pair $(\text{Mod}_ R, \otimes )$, such as the category of algebras.


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