added tail function

diff --git a/helm/matita/library/list/list.ma b/helm/matita/library/list/list.ma
index 72637c357226ae4c0c51304d4b73b246958b61aa..d5664f4166c783914af3be60f1d60bc25a008a79 100644 (file)
--- a/helm/matita/library/list/list.ma
+++ b/helm/matita/library/list/list.ma
@@ -56,6 +56,11 @@ let rec append A (l1: list A) l2 on l1 :=
   [ nil => l2
   | (cons hd tl) => hd :: append A tl l2 ].
 
+definition tail := \lambda A:Set. \lambda l: list A.
+  match l with
+  [ nil => []
+  | (cons hd tl) => tl].
+
 interpretation "append" 'append l1 l2 = (cic:/matita/list/append.con _ l1 l2).
 
 theorem append_nil: \forall A:Set.\forall l:list A.l @ [] = l.