∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {X₁ X₂ : C} {f : X₁ ⟶ X₂} {Y₁ Y₂ : C} {f' : Y₁ ⟶ Y₂}
  (e : CategoryTheory.Arrow.mk f ≅ CategoryTheory.Arrow.mk f'),
  CategoryTheory.CategoryStruct.comp f (CategoryTheory.Arrow.rightFunc.mapIso e).hom =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.Arrow.leftFunc.mapIso e).hom f'