    sig
      type ('a, 'b) t
      val create : int -> ('a, 'b) Hashtbl.t
      val clear : ('a, 'b) Hashtbl.t -> unit
      val add : ('a, 'b) Hashtbl.t -> 'a -> 'b -> unit
      val copy : ('a, 'b) Hashtbl.t -> ('a, 'b) Hashtbl.t
      val find : ('a, 'b) Hashtbl.t -> 'a -> 'b
      val find_all : ('a, 'b) Hashtbl.t -> 'a -> 'b list
      val mem : ('a, 'b) Hashtbl.t -> 'a -> bool
      val remove : ('a, 'b) Hashtbl.t -> 'a -> unit
      val replace : ('a, 'b) Hashtbl.t -> 'a -> 'b -> unit
      val iter : ('a -> 'b -> unit) -> ('a, 'b) Hashtbl.t -> unit
      val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) Hashtbl.t -> 'c -> 'c
      module type HashedType =
        sig
          type t
          val equal : Hashtbl.HashedType.t -> Hashtbl.HashedType.t -> bool
          val hash : Hashtbl.HashedType.t -> int
        end
      module type S =
        sig
          type key
          and 'a t
          val create : int -> 'a Hashtbl.S.t
          val clear : 'a Hashtbl.S.t -> unit
          val copy : 'a Hashtbl.S.t -> 'a Hashtbl.S.t
          val add : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a -> unit
          val remove : 'a Hashtbl.S.t -> Hashtbl.S.key -> unit
          val find : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a
          val find_all : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a list
          val replace : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a -> unit
          val mem : 'a Hashtbl.S.t -> Hashtbl.S.key -> bool
          val iter : (Hashtbl.S.key -> 'a -> unit) -> 'a Hashtbl.S.t -> unit
          val fold :
            (Hashtbl.S.key -> 'a -> 'b -> 'b) -> 'a Hashtbl.S.t -> 'b -> 'b
        end
      module Make :
        functor (H : HashedType) ->
          sig
            type key = H.t
            and 'a t
            val create : int -> 'a Hashtbl.S.t
            val clear : 'a Hashtbl.S.t -> unit
            val copy : 'a Hashtbl.S.t -> 'a Hashtbl.S.t
            val add : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a -> unit
            val remove : 'a Hashtbl.S.t -> Hashtbl.S.key -> unit
            val find : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a
            val find_all : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a list
            val replace : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a -> unit
            val mem : 'a Hashtbl.S.t -> Hashtbl.S.key -> bool
            val iter : (Hashtbl.S.key -> 'a -> unit) -> 'a Hashtbl.S.t -> unit
            val fold :
              (Hashtbl.S.key -> 'a -> 'b -> 'b) -> 'a Hashtbl.S.t -> 'b -> 'b
          end
      val hash : 'a -> int
      external hash_param : int -> int -> 'a -> int = "hash_univ_param" "noalloc"
    end