(*********************************************)

(* Specifications: *)
Lemma not_left : forall p : nat, n <= p -> ~ occ t1 p.
Hint Resolve not_left: searchtrees.
(* directive lemmas *)
Lemma go_left : forall p : nat, occ (bin n t1 t2) p -> p < n -> occ t1 p.
(*****************************************************************)
Lemma go_right :
forall p : nat, occ (bin n t1 t2) p -> n < p -> occ t2 p.