∀ {C : Type u_4} {D : Type u_2} [inst : CategoryTheory.Category.{u_3, u_4} C]
  [inst_1 : CategoryTheory.Category.{u_1, 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) (a b : L.obj X ⟶ L.obj Y), a - b = a + -b