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