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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2010     *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(* The following module is a specialized version of [Hashtbl] that is
+   a better space saver. Actually, [Hashcons] instanciates [Hashtbl.t]
+   with [constr] used both as a key and as an image.  Thus, in each
+   cell of the internal bucketlist, there are two representations of
+   the same value. In this implementation, there is only one.
+
+   Besides, the responsibility of computing the hash function is now
+   given to the caller, which makes possible the interleaving of the
+   hash key computation and the hash-consing. *)
+
+module type Hashtype = sig
+  type t
+  val equals : t -> t -> bool
+end
+
+module type S = sig
+  type elt
+  (* [may_add_and_get key constr] uses [key] to look for [constr]
+     in the hash table [H]. If [constr] is in [H], returns the
+     specific representation that is stored in [H]. Otherwise,
+     [constr] is stored in [H] and will be used as the canonical
+     representation of this value in the future. *)
+  val may_add_and_get : int -> elt -> elt
+end
+
+module Make (E : Hashtype) : S with type elt = E.t
+
+module Combine : sig
+  val combine : int -> int -> int
+  val combinesmall : int -> int -> int
+  val combine3 : int -> int -> int -> int
+  val combine4 : int -> int -> int -> int -> int
+end