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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2015     *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(** This module defines existential variables, which are isomorphic to [int].
+    Nonetheless, casting from an [int] to a variable is deemed unsafe, so that
+    to keep track of such casts, one has to use the provided {!unsafe_of_int}
+    function. *)
+
+type t
+(** Type of existential variables. *)
+
+val repr : t -> int
+(** Recover the underlying integer. *)
+
+val unsafe_of_int : int -> t
+(** This is not for dummies. Do not use this function if you don't know what you
+    are doing. *)
+
+val equal : t -> t -> bool
+(** Equality over existential variables. *)
+
+val compare : t -> t -> int
+(** Comparison over existential variables. *)
+
+val hash : t -> int
+(** Hash over existential variables. *)
+
+module Set : Set.S with type elt = t
+module Map : CMap.ExtS with type key = t and module Set := Set