X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;ds=sidebyside;f=matita%2Fmatita%2Flib%2Fbasics%2Flists%2Flist.ma;h=ed988b760d283732144e949e2b8c189b4df46283;hb=7c9d99dfb049d726491b71f07ba6a9b088b30166;hp=39e25a9e980b9e6bcf9b582f59e6aa7455900bcb;hpb=85ecf862fa70864495c409d92417c8a45e4295d5;p=helm.git

diff --git a/matita/matita/lib/basics/lists/list.ma b/matita/matita/lib/basics/lists/list.ma
index 39e25a9e9..ed988b760 100644
--- a/matita/matita/lib/basics/lists/list.ma
+++ b/matita/matita/lib/basics/lists/list.ma
@@ -11,6 +11,7 @@
 
 include "basics/types.ma".
 include "arithmetics/nat.ma".
+include "basics/core_notation/card_1.ma".
 
 inductive list (A:Type[0]) : Type[0] :=
   | nil: list A
@@ -440,20 +441,29 @@ lemma unique_filter : ∀S,l,f.
   ]
 qed.
 
-lemma filter_eqb : ∀m,l. unique ? l → |filter ? (eqb m) l| ≤ 1.
-#m #l #Huni cut (∀lf. lf = filter ? (eqb m) l → |lf| ≤1) 
-  [2: #Hcut @Hcut %] 
-* // #a * // #b #tl #H @False_ind 
-cut (m=a) 
-  [@eqb_true_to_eq @(mem_filter_true ??? l) <H %1 %] #eqma
-cut (m=b) 
-  [@eqb_true_to_eq @(mem_filter_true ??? l) <H %2 %1 %] #eqmb
-@(absurd (unique ? (a::b::tl))) 
-  [>H @unique_filter // 
-  |<eqma <eqmb normalize % * * #H1 #_ @H1 %1 //
+lemma filter_eqb : ∀m,l. unique ? l → 
+  (mem ? m l ∧ filter ? (eqb m) l = [m])∨(¬mem ? m l ∧ filter ? (eqb m) l = []).
+#m #l elim l
+  [#_ %2 % [% @False_ind | //]
+  |#a #tl #Hind * #Hmema #Hunique
+   cases (Hind Hunique)
+    [* #Hmemm #Hind %1 % [%2 //]
+     >filter_false // @not_eq_to_eqb_false % #eqma @(absurd ? Hmemm) //
+    |* #Hmemm #Hind cases (decidable_eq_nat m a) #eqma 
+      [%1 <eqma % [%1 //] >filter_true [2: @eq_to_eqb_true //] >Hind //
+      |%2 % 
+        [@(not_to_not … Hmemm) * // #H @False_ind  @(absurd … H) //
+        |>filter_false // @not_eq_to_eqb_false @eqma
+        ]
+      ]
+    ]
   ]
-qed.  
-    
+qed.
+
+lemma length_filter_eqb: ∀m,l. unique ? l → 
+  |filter ? (eqb m) l| ≤ 1.
+#m #l #Huni cases (filter_eqb m l Huni) * #_ #H >H // 
+qed. 
 
 (***************************** split *******************************)
 let rec split_rev A (l:list A) acc n on n ≝