simple induction l; simpl in |- *; intros; auto with arith pts.
Qed.
Hint Resolve bd_app_list_ctxt: pts.

Lemma bd_whnf_rec :
forall (e : env) (t : term) (args : list term),
sn (ctxt beta_delta) e (app_list args t) ->
{u : term | red beta_delta e (app_list args t) u &
head_normal beta_delta e u}.