sig
type elt = int
type t
val create : unit -> t
val size : t -> int
val is_empty : t -> bool
val mem : t -> elt -> bool
val add : t -> elt -> unit
val remove : t -> elt -> unit
val clear : t -> unit
val iter : (elt -> unit) -> t -> unit
val iter_const : ('a -> elt -> unit) -> 'a -> t -> unit
val fold : ('a -> elt -> 'a) -> 'a -> t -> 'a
val fold_const : ('a -> 'b -> elt -> 'b) -> 'a -> 'b -> t -> 'b
end