proposition: Lemma bal_find : forall l x e r y, bst l -> bst r -> lt_tree x l -> gt_tree x r -> find y (bal l x e r) = find y (create l x e r).
proof: Proof. intros; rewrite find_mapsto_equiv; auto; intros; apply bal_mapsto. Qed.
imports: FunInd FMapInterface FMapList ZArith Int