intros key t data lookup_t above_t.
apply less_irrefl with key.
apply lookup_above_greater with t data; assumption.
Qed.
(*********************************************************)
(*		Definition is_below_avl		  	 *)
Inductive is_below_avl : avl_tree -> Int -> Prop :=
| Below_Avl_Nil : forall k0 : Int, is_below_avl Avl_Nil k0
| Below_Avl_Node :
forall (k : Int) (d : B) (l r : avl_tree) (b : bal) (k0 : Int),
Less k k0 -> is_below_avl r k0 -> is_below_avl (Avl_Node k d l r b) k0.

Lemma inv_below_avl_key :
forall (k : Int) (d : B) (l r : avl_tree) (b : bal) (k0 : Int),
is_below_avl (Avl_Node k d l r b) k0 -> Less k k0.