type t =
  | Pos of int list
  | Neg of int list
;;

val conj : t -> t -> t;;         (* union *)
val disj : t -> t -> t;;         (* intersection *)
val except : t -> t -> t;;       (* subtraction *)

val same : t -> t -> bool;;      (* equality test *)
val included : t -> t -> bool;;  (* inclusion test *)
val element : int -> t -> bool;; (* membership test *)

val finite : t -> bool;;
val infinite : t -> bool;;

val normalize : t -> t;;