Inductive wf_type (e : env) : term -> Prop :=
| wft_typed :
forall (T : term) (s : sort), typ e T (Srt s) -> wf_type e T
| wft_top : forall s : sort, wf_type e (Srt s).
Hint Resolve wft_top: pts.
Definition le_type_wf : red_rule :=
fun e => clos_refl_trans _ (fun x y => le_type e x y /\ wf_type e y).
(* Lemma le_type_wf_le: (e:env)(x,y:term)(le_type_wf e x y)->(le_type e x y). *)
Definition inv_typ (e : env) (t T : term) (P : Prop) : Prop :=
match t with
| Srt s1 => forall s2 : sort, axiom s1 s2 -> le_type e (Srt s2) T -> P
| Ref n =>
forall x : decl,
item x e n -> le_type e (lift (S n) (typ_of_decl x)) T -> P
| Abs A M =>
forall (s : sort) (U : term),
typ (Ax A :: e) M U ->
typ e (Prod A U) (Srt s) -> le_type e (Prod A U) T -> P
| App u v =>
forall Ur V : term,
typ e v V -> typ e u (Prod V Ur) -> le_type e (subst v Ur) T -> P
| Prod A B =>
forall s1 s2 s3 : sort,
rule s1 s2 s3 ->
typ e A (Srt s1) ->
typ (Ax A :: e) B (Srt s2) -> le_type e (Srt s3) T -> P
end.

Theorem inv_typ_conv :
forall (e : env) (t U V : term),
le_type e U V -> forall P : Prop, inv_typ e t V P -> inv_typ e t U P.