diff --git a/univ.ml b/univ.ml
new file mode 100644
index 00000000..c18aa117
--- /dev/null
+++ b/univ.ml
@@ -0,0 +1,67 @@
+(*
+Copyright (c) 2013, Simon Cruanes
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+Redistributions of source code must retain the above copyright notice, this
+list of conditions and the following disclaimer.  Redistributions in binary
+form must reproduce the above copyright notice, this list of conditions and the
+following disclaimer in the documentation and/or other materials provided with
+the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*)
+
+(** {1 Universal type} *)
+
+(** This is largely inspired by https://ocaml.janestreet.com/?q=node/18 . *)
+
+type t = { 
+  mutable id : unit ref;
+  mutable store : unit -> unit;
+} (** The universal type *)
+
+type 'a embedding = {
+  pack : 'a -> t;           (** Pack a 'a into a univ value *)
+  unpack : t -> 'a option;  (** Try to unpack the univ value into an 'a *)
+  set : t -> 'a -> unit;    (** Change, in-place, the content of the univ value *)
+  compatible : t -> bool;   (** Check whether the univ value can be unpacked *)
+} (** Conversion between the universal type and 'a *)
+
+(** Create a new embedding. Values packed by a given embedding can
+    only be unpacked by the same embedding. *)
+let embed () = 
+  let id = ref () in  (* unique ID of the embedding *)
+  let r = ref None in (* place to store values *)
+  let pack a =        (* pack the 'a value into a new univ cell *)
+    let o = Some a in
+    { id = id; store = (fun () -> r := o); }
+  in
+  let unpack t =      (* try to extract the content of a univ cell *)
+    if id == t.id then begin
+      t.store ();
+      let a = !r in
+      r := None;
+      a
+    end else None
+  in
+  let set t a =       (* change, in place, the embedding and content of the cell *)
+    t.id <- id;
+    let o = Some a in
+    t.store <- (fun () -> r := o)
+  in
+  let compatible t =  (* check whether the univ cell is from this embedding *)
+    id == t.id
+  in
+  { pack; unpack; compatible; set; }
diff --git a/univ.mli b/univ.mli
new file mode 100644
index 00000000..0cd88b55
--- /dev/null
+++ b/univ.mli
@@ -0,0 +1,42 @@
+(*
+Copyright (c) 2013, Simon Cruanes
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+Redistributions of source code must retain the above copyright notice, this
+list of conditions and the following disclaimer.  Redistributions in binary
+form must reproduce the above copyright notice, this list of conditions and the
+following disclaimer in the documentation and/or other materials provided with
+the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*)
+
+(** {1 Universal type} *)
+
+(** This is largely inspired by https://ocaml.janestreet.com/?q=node/18 . *)
+
+type t
+  (** The universal type *)
+
+type 'a embedding = {
+  pack : 'a -> t;           (** Pack a 'a into a univ value *)
+  unpack : t -> 'a option;  (** Try to unpack the univ value into an 'a *)
+  set : t -> 'a -> unit;    (** Change, in-place, the content of the univ value *)
+  compatible : t -> bool;   (** Check whether the univ value can be unpacked *)
+} (** Conversion between the universal type and 'a *)
+
+val embed : unit -> 'a embedding
+  (** Create a new embedding. Values packed by a given embedding can
+      only be unpacked by the same embedding. *)