proposition: Lemma Exists_eq_count_pos : forall P l, Exists P l = (count P l > 0).
proof: Proof. Proof using. intros. rewrite LibList.Exists_eq_count_pos. unfold count. rewrite abs_nonneg; math. Qed.
imports: TLC(LibTactics LibLogic LibOperation LibReflect LibProd LibNat LibInt LibOption LibWf) TLC(LibInt)