(* inserting at the root ; please notice that the most recent value is stored *)

(* Specifications: *)
Lemma insert_eq :
forall (n : key) (v v' : data) (t1 t2 : btree),
search_tree (bnode n v t1 t2) ->
INSERT n v' (bnode n v t1 t2) (bnode n v' t1 t2).