proposition: Lemma Exists_of_count_pos : forall P l, count P l > 0 -> Exists P l.
proof: Proof. Proof using. introv. rewrite~ Exists_eq_count_pos. Qed.
imports: TLC(LibTactics LibLogic LibOperation LibReflect LibProd LibNat LibInt LibOption LibWf) TLC(LibInt)