import prelude

data Nat : Type where
	Zero : Nat
  	Succ : (n:Nat) -> Nat

add_Nat : Add Nat
add_Nat = rec zero = Zero
	      plus = natPlus

natPlus : Nat -> Nat -> Nat
natPlus Zero y = y
natPlus (Succ x) y = Succ (natPlus x y)

pred : Nat -> Nat
pred Zero = Zero
pred (Succ n) = n

natToInt : Nat -> Integer
natToInt Zero = 0
natToInt (Succ n) = 1 + natToInt n

intToNat : Integer -> Nat
intToNat n = if n == 0 then Zero else Succ (intToNat (n-1))