∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {X : C} (Y Z : CategoryTheory.Over X)
  [inst_1 : CategoryTheory.Limits.HasPullback Y.hom Z.hom] [inst_2 : CategoryTheory.Limits.HasBinaryProduct Y Z]
  {Z_1 : C} (h : Z.left ⟶ Z_1),
  CategoryTheory.CategoryStruct.comp (Y.prodLeftIsoPullback Z).hom
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullback.snd Y.hom Z.hom) h) =
    CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.prod.snd.left h