∀ {X Y Z : TopCat} (f : X ⟶ Z) (g : Y ⟶ Z) {Z_1 : TopCat} (h : X ⟶ Z_1),
  CategoryTheory.CategoryStruct.comp (TopCat.pullbackIsoProdSubtype f g).inv
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullback.fst f g) h) =
    CategoryTheory.CategoryStruct.comp (TopCat.pullbackFst f g) h