∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {D : Type u_1} [inst_1 : CategoryTheory.Category.{v_1, u_1} D]
  {X Y : CategoryTheory.Functor (CategoryTheory.WithInitial C) D} (η : X ⟶ Y),
  (CategoryTheory.WithInitial.equivComma.functor.map η).left = η.app CategoryTheory.WithInitial.star