∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {X Y Z X' Y' Z' : C} (iX : X ≅ X') (iY : Y ≅ Y') (iZ : Z ≅ Z')
  {f : X ⟶ Y} {g : X ⟶ Z} {f' : X' ⟶ Y'} {g' : X' ⟶ Z'}
  (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom)
  (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom),
  (CategoryTheory.Limits.spanExt iX iY iZ wf wg).inv.app CategoryTheory.Limits.WalkingSpan.left = iY.inv