∀ {R : Type u_2} [inst : Ring R] (P Q R_1 : ModuleCat R) (f f' : P ⟶ Q) (g : Q ⟶ R_1),
  CategoryTheory.CategoryStruct.comp (f + f') g =
    CategoryTheory.CategoryStruct.comp f g + CategoryTheory.CategoryStruct.comp f' g