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diff --git a/matita/matita/lib/basics/deqlist.ma b/matita/matita/lib/basics/deqlist.ma
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+(*
+    ||M||  This file is part of HELM, an Hypertextual, Electronic        
+    ||A||  Library of Mathematics, developed at the Computer Science     
+    ||T||  Department of the University of Bologna, Italy.                     
+    ||I||                                                                 
+    ||T||  
+    ||A||  
+    \   /  This file is distributed under the terms of the       
+     \ /   GNU General Public License Version 2   
+      V_______________________________________________________________ *)
+
+include "basics/deqsets.ma".
+include "basics/lists/listb.ma".
+
+(*
+
+record DeqSet : Type[1] ≝ { 
+   carr :> Type[0];
+   eqb: carr → carr → bool;
+   eqb_true: ∀x,y. (eqb x y = true) ↔ (x = y)
+}. *)
+    
+
+(* list *)
+
+let rec eq_list (A:DeqSet) (l1,l2:list A) on l1 ≝
+  match l1 with 
+  [ nil ⇒ match l2 with [nil ⇒ true | _ ⇒ false]
+  | cons a1 tl1 ⇒ 
+      match l2 with [nil ⇒ false | cons a2 tl2 ⇒ a1 ==a2 ∧ eq_list A tl1 tl2]].
+
+lemma eq_list_true: ∀A:DeqSet.∀l1,l2:list A.
+  eq_list A l1 l2 = true ↔ l1 = l2.
+#A #l1 elim l1
+  [* [% // |#a #tl % normalize #H destruct ]
+  |#a1 #tl1 #Hind *  
+    [normalize % #H destruct
+    |#a2 #tl2 normalize %
+      [cases (true_or_false (a1==a2)) #Heq >Heq normalize 
+        [#Htl >(\P Heq) >(proj1 … (Hind tl2) Htl) // | #H destruct ]
+      |#H destruct >(\b (refl … )) >(proj2 … (Hind tl2) (refl …)) //
+      ]
+    ]
+  ]
+qed.
+
+definition DeqList ≝ λA:DeqSet.
+  mk_DeqSet (list A) (eq_list A) (eq_list_true A).
+  
+unification hint  0 ≔ C; 
+    T ≟ carr C,
+    X ≟ DeqList C
+(* ---------------------------------------- *) ⊢ 
+    list T ≡ carr X.
+
+alias id "eqb" = "cic:/matita/basics/deqsets/eqb#fix:0:0:3".
+alias symbol "hint_decl" (instance 1) = "hint_decl_Type0".
+unification hint  0 ≔ T,a1,a2; 
+    X ≟ DeqList T
+(* ---------------------------------------- *) ⊢ 
+    eq_list T a1 a2 ≡ eqb X a1 a2.
+
+