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diff --git a/helm/software/lambda-delta/src/common/alpha.ml b/helm/software/lambda-delta/src/common/alpha.ml
new file mode 100644
index 000000000..01c2aafe8
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+++ b/helm/software/lambda-delta/src/common/alpha.ml
@@ -0,0 +1,39 @@
+(*
+    ||M||  This file is part of HELM, an Hypertextual, Electronic        
+    ||A||  Library of Mathematics, developed at the Computer Science     
+    ||T||  Department, University of Bologna, Italy.                     
+    ||I||                                                                
+    ||T||  HELM is free software; you can redistribute it and/or         
+    ||A||  modify it under the terms of the GNU General Public License   
+    \   /  version 2 or (at your option) any later version.              
+     \ /   This software is distributed as is, NO WARRANTY.              
+      V_______________________________________________________________ *)
+
+module Y = Entity
+
+(* internal functions *******************************************************)
+
+let rec rename ns n =
+   let token, mode = n in
+   let n = token ^ "_", mode in
+   if List.mem n ns then rename ns n else n
+
+let alpha_name acc attr =
+   let ns, a = acc in
+   match attr with
+      | Y.Name n ->
+	 if List.mem n ns then
+            let n = rename ns n in
+	    n :: ns, Y.Name n :: a
+	 else 
+	    n :: ns, attr :: a
+      | _        -> assert false 
+
+(* interface functions ******************************************************)
+
+let alpha ns a =
+   let f a names =
+      let _, names = List.fold_left alpha_name (ns, []) (List.rev names) in
+      List.rev_append a names
+   in
+   Y.get_names f a