proposition: Lemma create_height : forall l x e r `{!Avl l, !Avl r}, -(2) <= height l - height r <= 2 -> height (create l x e r) = max (height l) (height r) + 1.
proof: Proof. unfold create; autom. Qed.
imports: Coq(ZArith Int Lia PeanoNat FunInd Orders) MMaps(GenTree AVL)