∀ {C : Type u_4} [inst : CategoryTheory.Category.{u_3, u_4} C] {D : Type u_2}
  [inst_1 : CategoryTheory.Category.{u_1, u_2} D] [inst_2 : CategoryTheory.Preadditive D]
  {F : CategoryTheory.Functor C D} (hF : F.FullyFaithful) (P Q R : C) (f f' : P ⟶ Q) (g : Q ⟶ R),
  F.map (CategoryTheory.CategoryStruct.comp (f + f') g) =
    F.map (CategoryTheory.CategoryStruct.comp f g + CategoryTheory.CategoryStruct.comp f' g)