proposition: Lemma count_rev : forall P l, count P (rev l) = count P l.
proof: Proof. Proof using. intros. unfold count. rew_listx~. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)