intros p; elim p; simpl in |- *; auto;
try (intros p0; case (compute_pbcode p0); simpl in |- *; auto);
intros; red in |- *; intros HH1; discriminate.
Qed.
Hint Resolve compute_pbcode_not_null : core.

(* Specifications: *)
(* Keys in the computed code are leaves of the tree *)
Theorem in_pbcompute_inpb :
forall (t : pbtree) (a : A) (l : list bool),
In (a, l) (compute_pbcode t) -> inpb (pbleaf a) t.