val mem : elt -> t -> bool
val remove : elt -> t -> t
val compare : t -> t -> int
val equal : t -> t -> bool
val subset : t -> t -> bool
val iter : ( elt -> unit ) -> t -> unit
val fold : ( elt -> 'a -> 'a ) -> t -> 'a -> 'a
val for_all : ( elt -> bool ) -> t -> bool
val exists : ( elt -> bool ) -> t -> bool
val filter : ( elt -> bool ) -> t -> t
val partition : ( elt -> bool ) -> t -> t * t
val elements : t -> elt list
val split : elt -> t -> t * bool * t