∀ {T : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} T] (X : T)
  (self : CategoryTheory.Comma (CategoryTheory.Functor.id T) (CategoryTheory.Functor.fromPUnit X)),
  (CategoryTheory.Over.forgetCocone X).ι.app self = self.hom