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diff --git a/matita/matita/nlibrary/basics/list2.ma b/matita/matita/nlibrary/basics/list2.ma
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+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||         The HELM team.                                      *)
+(*      ||A||         http://helm.cs.unibo.it                             *)
+(*      \   /                                                             *)
+(*       \ /        This file is distributed under the terms of the       *)
+(*        v         GNU General Public License Version 2                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+include "basics/list.ma".
+include "arithmetics/nat.ma".
+
+nlet rec length (A:Type) (l:list A) on l ≝ 
+  match l with 
+    [ nil ⇒ 0
+    | cons a tl ⇒ S (length A tl)].
+
+notation "|M|" non associative with precedence 60 for @{'norm $M}.
+interpretation "norm" 'norm l = (length ? l).
+
+nlet rec nth n (A:Type) (l:list A) (d:A)  ≝  
+  match n with
+    [O ⇒ hd A l d
+    |S m ⇒ nth m A (tail A l) d].
+