X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Flist%2Fsort.ma;h=c67b28227101efee63462b06b59020441638b945;hb=f48faa46342b557486e06c17fd574d1eeb386239;hp=d182ed6d68bd1148b663a3d494cd18baf996d306;hpb=c5608d2704215a7004d23f4801e19df3939f0285;p=helm.git

diff --git a/helm/software/matita/library/list/sort.ma b/helm/software/matita/library/list/sort.ma
index d182ed6d6..c67b28227 100644
--- a/helm/software/matita/library/list/sort.ma
+++ b/helm/software/matita/library/list/sort.ma
@@ -12,22 +12,29 @@
 (*                                                                        *)
 (**************************************************************************)
 
-set "baseuri" "cic:/matita/list/sort/".
-
 include "datatypes/bool.ma".
 include "datatypes/constructors.ma".
-include "list/list.ma".
+include "list/in.ma".
+
+inductive sorted (A:Type) (P:A \to A \to Prop): list A \to Prop \def
+| sort_nil : sorted A P []
+| sort_cons : \forall x,l.sorted A P l \to (\forall y.in_list ? y l \to P x y)
+              \to sorted A P (x::l).
+              
+lemma sorted_cons_to_sorted : \forall A,P,x,l.sorted A P (x::l) \to sorted A P l.
+intros;inversion H;intros
+  [destruct H1
+  |destruct H4;assumption]
+qed.
+
+lemma sorted_to_minimum : \forall A,P,x,l.sorted A P (x::l) \to 
+                          \forall y.in_list ? y l \to P x y.
+intros;inversion H;intros;
+  [destruct H2
+  |destruct H5;apply H4;assumption]
+qed.
+
 
-let rec mem (A:Type) (eq: A → A → bool) x (l: list A) on l ≝
- match l with
-  [ nil ⇒ false
-  | (cons a l') ⇒
-    match eq x a with
-     [ true ⇒ true
-     | false ⇒ mem A eq x l'
-     ]
-  ].
-  
 let rec ordered (A:Type) (le: A → A → bool) (l: list A) on l ≝
  match l with
   [ nil ⇒ true
@@ -39,6 +46,45 @@ let rec ordered (A:Type) (le: A → A → bool) (l: list A) on l ≝
       ]
   ].
   
+lemma sorted_to_eq_sorted_b_true :
+      \forall A,ord,ordb.
+      (\forall x,y.ord x y \to ordb x y = true) \to 
+      \forall l.sorted A ord l \to ordered A ordb l = true.
+intros 5;elim l
+  [reflexivity
+  |simplify;rewrite > H1;generalize in match H2;cases l1;intros
+     [reflexivity
+     |simplify;rewrite > H
+        [reflexivity
+        |apply (sorted_to_minimum ? ? ? ? H3);apply in_list_head]
+     |apply sort_nil
+     |apply (sorted_cons_to_sorted ? ? ? ? H3)]]
+qed.
+
+(* 
+   TODO
+   per far funzionare questa dimostrazione bisogna appoggiarsi a un
+   eqb (e utilizzare quindi in_list <-> mem), oppure modificare la definizione 
+   di sorted in modo che non si appoggi più a in_list:
+   sorted []
+   sorted [x] per ogni x
+   sorted x::y::l se ord x y e sorted y::l
+
+lemma eq_sorted_b_true_to_sorted :
+      \forall A,ord,ordb.
+      (\forall x,y.ordb x y = true \to ord x y) \to
+      \forall l.ordered A ordb l = true \to sorted A ord l.
+intros 5;elim l
+  [apply sort_nil
+  |apply sort_cons
+     [apply H1;simplify in H2;generalize in match H2;cases l1;intros
+        [reflexivity
+        |simplify in H3;simplify;apply (andb_true_true_r ? ? H3)]
+     |intros;apply H;generalize in match H2;
+      generalize in match (in_list_to_mem_true ? ? ? ? H
+        [
+*)
+
 let rec insert (A:Type) (le: A → A → bool) x (l: list A) on l ≝
  match l with
   [ nil ⇒ [x]