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diff --git a/matita/matita/contribs/lambdadelta/bin/xhtbl/fold.ml b/matita/matita/contribs/lambdadelta/bin/xhtbl/fold.ml
new file mode 100644
index 000000000..752b06d77
--- /dev/null
+++ b/matita/matita/contribs/lambdadelta/bin/xhtbl/fold.ml
@@ -0,0 +1,25 @@
+module T = Table
+
+type 'a fold_cb = {
+   open_table : 'a -> T.table -> 'a;
+   close_table: 'a -> T.table -> 'a;
+   map_key    : 'a -> T.key -> 'a;
+   open_line  : bool -> 'a -> 'a;
+   close_line : bool -> 'a -> 'a;
+   open_entry : bool -> 'a -> 'a;   
+   close_entry: bool -> 'a -> 'a -> 'a;
+}
+
+let map h g f a b = h a (g (f a) b)
+
+let rec fold_table cb a t =
+   let a = cb.open_table a t in
+   let a = fold_entry cb a t.T.te in
+   cb.close_table a t
+
+and fold_entry cb a = function
+   | T.Key k        -> cb.map_key a k
+   | T.Line (r, ts) ->
+      let a = cb.open_line r a in
+      let a = List.fold_left (map (cb.close_entry r) (fold_table cb) (cb.open_entry r)) a ts in
+      cb.close_line r a