∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] (G : CategoryTheory.Functor C (Type w))
  (X : CategoryTheory.Grothendieck (G.comp CategoryTheory.typeToCat)),
  ((CategoryTheory.Grothendieck.grothendieckTypeToCat G).functor.obj X).snd = X.fiber.as