∀ {J : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} J] {C : Type u₃} [inst_1 : CategoryTheory.Category.{v₃, u₃} C]
  {D : Type u₄} [inst_2 : CategoryTheory.Category.{v₄, u₄} D] {F : CategoryTheory.Functor J C}
  {H H' : CategoryTheory.Functor C D} (α : H ≅ H') (c : CategoryTheory.Limits.Cone F),
  (CategoryTheory.Functor.postcomposeWhiskerLeftMapCone α c).hom.hom = α.hom.app c.pt