∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {T T' : D} {S : CategoryTheory.Functor C D} (i : T ≅ T')
  (X : CategoryTheory.Comma S (CategoryTheory.Functor.fromPUnit T')),
  ((CategoryTheory.CostructuredArrow.mapIso i).inverse.obj X).left = X.left