∀ {C : Type u_1} {D : Type u_2} [inst : CategoryTheory.Category.{v_1, u_1} C]
  [inst_1 : CategoryTheory.Category.{v_2, u_2} D] [inst_2 : CategoryTheory.Preadditive C]
  {L : CategoryTheory.Functor C D} (W : CategoryTheory.MorphismProperty C) [inst_3 : L.IsLocalization W]
  [inst_4 : W.HasLeftCalculusOfFractions] {X Y : C} (f₁ f₂ : X ⟶ Y),
  CategoryTheory.Localization.Preadditive.add' W (L.map f₁) (L.map f₂) = L.map (f₁ + f₂)