--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+include "ground_2/notation/constructors/nil_1.ma".
+include "ground_2/notation/constructors/nil_2.ma".
+include "ground_2/notation/constructors/cons_3.ma".
+include "ground_2/notation/constructors/cons_5.ma".
+include "ground_2/notation/functions/append_2.ma".
+include "ground_2/lib/arith.ma".
+
+(* LISTS ********************************************************************)
+
+inductive list (A:Type[0]) : Type[0] :=
+ | nil : list A
+ | cons: A → list A → list A.
+
+interpretation "nil (list)" 'Nil A = (nil A).
+
+interpretation "cons (list)" 'Cons A hd tl = (cons A hd tl).
+
+let rec all A (R:predicate A) (l:list A) on l ≝
+ match l with
+ [ nil ⇒ ⊤
+ | cons hd tl ⇒ R hd ∧ all A R tl
+ ].
+
+inductive list2 (A1,A2:Type[0]) : Type[0] :=
+ | nil2 : list2 A1 A2
+ | cons2: A1 → A2 → list2 A1 A2 → list2 A1 A2.
+
+interpretation "nil (list of pairs)" 'Nil A1 A2 = (nil2 A1 A2).
+
+interpretation "cons (list of pairs)" 'Cons A1 A2 hd1 hd2 tl = (cons2 A1 A2 hd1 hd2 tl).
+
+let rec append2 (A1,A2:Type[0]) (l1,l2:list2 A1 A2) on l1 ≝ match l1 with
+[ nil2 ⇒ l2
+| cons2 a1 a2 tl ⇒ {a1, a2} @ append2 A1 A2 tl l2
+].
+
+interpretation "append (list of pairs)"
+ 'Append l1 l2 = (append2 ? ? l1 l2).
+
+let rec length2 (A1,A2:Type[0]) (l:list2 A1 A2) on l ≝ match l with
+[ nil2 ⇒ 0
+| cons2 _ _ l ⇒ length2 A1 A2 l + 1
+].
+
+interpretation "length (list of pairs)"
+ 'card l = (length2 ? ? l).