proposition: Lemma count_app : forall P l1 l2, count P (l1++l2) = count P l1 + count P l2.
proof: Proof. Proof using. gowith LibList.count_app. Qed.
imports: TLC(LibTactics LibLogic LibOperation LibReflect LibProd LibNat LibInt LibOption LibWf) TLC(LibInt)