(* The following lemma looks like an inversion of [JTyAbs], but it
   is not truly one, because it is proved by applying weakening and
   [JTyApp], hence increasing the height of the derivation by one. *)

Goal (* phony_inversion_JTyAbs: *)
  forall n E t T,
  j n E t (TyForall T) ->
  j (S n) (map (shift 0) E) t T.

Lemma canonicalization: forall n E t T, j n E (TAbs t) T -> j 0 E (TAbs t) T.