Definition 10.77.1. Let R be a ring. An R-module P is projective if and only if the functor \mathop{\mathrm{Hom}}\nolimits _ R(P, -) : \text{Mod}_ R \to \text{Mod}_ R is an exact functor.
Definition 10.77.1. Let R be a ring. An R-module P is projective if and only if the functor \mathop{\mathrm{Hom}}\nolimits _ R(P, -) : \text{Mod}_ R \to \text{Mod}_ R is an exact functor.
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