∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {X Y Z : C} (α : X ≅ Y) {f : Z ⟶ Y} {g : Z ⟶ X},
  (CategoryTheory.CategoryStruct.comp g α.hom = f) = (g = CategoryTheory.CategoryStruct.comp f α.inv)