X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Flib%2Fbasics%2Flist.ma;h=798f5762933b3fd9c1d2153761e08d33e31dc689;hb=fe4df66869250943913c7fa534bb22305a320683;hp=4d99c59c8e3364f4ef0b71fd3c1227ad444f9bc1;hpb=53452958508001e7af3090695b619fe92135fb9e;p=helm.git

diff --git a/matita/matita/lib/basics/list.ma b/matita/matita/lib/basics/list.ma
index 4d99c59c8..798f57629 100644
--- a/matita/matita/lib/basics/list.ma
+++ b/matita/matita/lib/basics/list.ma
@@ -10,7 +10,7 @@
       V_______________________________________________________________ *)
 
 include "basics/types.ma".
-include "basics/bool.ma".
+include "arithmetics/nat.ma".
 
 inductive list (A:Type[0]) : Type[0] :=
   | nil: list A
@@ -114,6 +114,21 @@ match l1 with
   | cons a tl ⇒ (map ??(dp ?? a) (g a)) @ dprodl A f tl g
   ].
 
+(**************************** length ******************************)
+
+let rec length (A:Type[0]) (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).
+
+let rec nth n (A:Type[0]) (l:list A) (d:A)  ≝  
+  match n with
+    [O ⇒ hd A l d
+    |S m ⇒ nth m A (tail A l) d].
+
 (**************************** fold *******************************)
 
 let rec fold (A,B:Type[0]) (op:B → B → B) (b:B) (p:A→bool) (f:A→B) (l:list A) on l :B ≝