+inductive pos: Set \def
+| one : pos
+| next : pos \to pos.
-Inductive nat : Set \def
+inductive nat:Set \def
| O : nat
| S : nat \to nat.
-Inductive list (A:Set) : Set \def
-| nil : list A
-| cons : A \to list A \to list A.
+inductive int: Set \def
+| positive: nat \to int
+| negative : nat \to int.
-Inductive bool: Set \def
-| true : bool
-| false : bool.
+inductive empty : Set \def .
+let rec pos2nat x \def
+ match x with
+ [ one \Rightarrow (S O)
+ | (next z) \Rightarrow S (pos2nat z)].
+
+let rec nat2int x \def
+ match x with
+ [ O \Rightarrow positive O
+ | (S z) \Rightarrow positive (S z)].
+
+coercion pos2nat.
+
+coercion nat2int.
+
+let rec plus x y \def
+ match x with
+ [ (positive n) \Rightarrow x
+ | (negative z) \Rightarrow y].
+
+theorem a: plus O one.
-let rec len (A:Set)(l:list A) on l : nat \def
- match l:list with [
- nil \Rightarrow O
- | (cons e tl) \Rightarrow (S (len A tl))].
-let rec plus (n,m:nat) : nat \def
- match n:nat with [
- O \Rightarrow m
- | (S x) \Rightarrow (S (plus x m)) ].
-let rec is_zero (n:nat) : bool \def
- match n:nat with [
- O \Rightarrow true
- | (S x) \Rightarrow false].
-let rec nat_eq_dec (n,m:nat) : bool \def
- match n:nat with [
- O \Rightarrow
- match m:nat with [
- O \Rightarrow true
- | (S x) \Rightarrow false]
- | (S x) \Rightarrow
- match m:nat with [
- O \Rightarrow false
- | (S y) \Rightarrow (nat_eq_dec x y)]
- ].
-Coercion is_zero.
-Coercion len.
-Print Coer.
-Print Env.