sig
type t = Indexer.Make(Wpo.S).t
val size : t -> int
val mem : Wpo.S.t -> t -> bool
val get : int -> t -> Wpo.S.t
val index : Wpo.S.t -> t -> int
val empty : t
val add : Wpo.S.t -> t -> t
val remove : Wpo.S.t -> t -> t
val filter : (Wpo.S.t -> bool) -> t -> t
val update : Wpo.S.t option -> Wpo.S.t option -> t -> int * int * t
val iter : (Wpo.S.t -> unit) -> t -> unit
val iteri : (int -> Wpo.S.t -> unit) -> t -> unit
end