simple induction 2; intros.
apply type_conv with T s; auto with arith pts.
apply type_conv_srt with T; auto with arith pts.
Qed.

(* Specifications: *)
Theorem wf_type_prod_l :
forall (e : env) (A B : term), wf_type e (Prod A B) -> wf_type e A.
Theorem wf_type_prod_l :
forall (e : env) (A B : term), wf_type e (Prod A B) -> wf_type e A.