X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Flist%2Flist.ma;h=077e1af6c443682939461692d20bdfc20f60be22;hb=a149b1474110583ea5f47fa5bcb85554bba92f19;hp=c6fd212beca5b6f8b623b39cf95bee3508c48fac;hpb=e78cf74f8976cf0ca554f64baa9979d0423ee927;p=helm.git

diff --git a/helm/software/matita/library/list/list.ma b/helm/software/matita/library/list/list.ma
index c6fd212be..077e1af6c 100644
--- a/helm/software/matita/library/list/list.ma
+++ b/helm/software/matita/library/list/list.ma
@@ -109,8 +109,8 @@ with permut1 : list A -> list A -> Prop \def
   | step : \forall l1,l2:list A. \forall x,y:A. 
       permut1 ? (l1 @ (x :: y :: l2)) (l1 @ (y :: x :: l2)).
 
-include "nat/nat.ma".  
-   
+(*
+
 definition x1 \def S O.
 definition x2 \def S x1.
 definition x3 \def S x2.
@@ -121,15 +121,9 @@ theorem tmp : permutation nat (x1 :: x2 :: x3 :: []) (x1 :: x3 :: x2 :: []).
   apply (step ? (x1::[]) [] x2 x3).
   qed. 
 
-
-(*
 theorem nil_append_nil_both:
   \forall A:Type.\forall l1,l2:list A.
     l1 @ l2 = [] \to l1 = [] \land l2 = [].
-*)
-
-(*
-include "nat/nat.ma".
 
 theorem test_notation: [O; S O; S (S O)] = O :: S O :: S (S O) :: []. 
 reflexivity.
@@ -139,6 +133,7 @@ theorem test_append: [O;O;O;O;O;O] = [O;O;O] @ [O;O] @ [O].
 simplify.
 reflexivity.
 qed.
+
 *)
 
 definition nth ≝
@@ -200,3 +195,9 @@ intros;elim l
      [simplify;apply le_S_S;assumption
      |simplify;apply le_S;assumption]]
 qed.
+
+lemma length_append : ∀A,l,m.length A (l@m) = length A l + length A m.
+intros;elim l
+[reflexivity
+|simplify;rewrite < H;reflexivity]
+qed.