module type S = sig
  type elt

  type t

  type 'a map

  val empty : t

  val is_empty : t -> bool

  val mem : t -> elt -> bool

  val add : t -> elt -> t

  val singleton : elt -> t

  val remove : t -> elt -> t

  val union : t -> t -> t

  val inter : t -> t -> t

  val diff : t -> t -> t

  val compare : t -> t -> Ordering.t

  val equal : t -> t -> bool

  val is_subset : t -> of_:t -> bool

  val iter : t -> f:(elt -> unit) -> unit

  val map : t -> f:(elt -> elt) -> t

  val fold : t -> init:'a -> f:(elt -> 'a -> 'a) -> 'a

  val for_all : t -> f:(elt -> bool) -> bool

  val exists : t -> f:(elt -> bool) -> bool

  val filter : t -> f:(elt -> bool) -> t

  val partition : t -> f:(elt -> bool) -> t * t

  val cardinal : t -> int

  val min_elt : t -> elt option

  val max_elt : t -> elt option

  val choose : t -> elt option

  val choose_exn : t -> elt

  val split : t -> elt -> t * bool * t

  val of_list : elt list -> t

  val of_list_map : 'a list -> f:('a -> elt) -> t

  val to_list : t -> elt list

  (** Convert to a list and map every element. *)
  val to_list_map : t -> f:(elt -> 'a) -> 'a list

  val find : t -> f:(elt -> bool) -> elt option

  val union_all : t list -> t

  val union_map : 'a list -> f:('a -> t) -> t

  val to_dyn : t -> Dyn.t

  val of_keys : _ map -> t

  val to_map : t -> f:(elt -> 'a) -> 'a map
end
