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diff --git a/helm/software/lambda-delta/src/common/level.ml b/helm/software/lambda-delta/src/common/level.ml
new file mode 100644
index 000000000..d33c1be66
--- /dev/null
+++ b/helm/software/lambda-delta/src/common/level.ml
@@ -0,0 +1,37 @@
+(*
+    ||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_______________________________________________________________ *)
+
+type level = int option
+
+(* Interface functions ******************************************************)
+
+let infinite = None
+
+let finite i = Some i
+
+let is_zero xi = 
+   xi = (Some 0)
+
+let is_infinite xi =
+   xi = None
+
+let succ = function
+   | None   -> None
+   | Some i -> Some (succ i)
+
+let pred = function
+   | None              -> None
+   | Some i when i > 0 -> Some (pred i)
+   | _                 -> Some 0
+
+let to_string = function
+   | None   -> ""
+   | Some i -> string_of_int i