∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {X Y Z : C} (f : X ⟶ Y) (g : X ⟶ Z)
  [inst_1 : CategoryTheory.IsIso f] {Z_1 : C} (h : Z ⟶ Z_1),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushout.inl f g)
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.inv (CategoryTheory.Limits.pushout.inr f g)) h) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.inv f) (CategoryTheory.CategoryStruct.comp g h)