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