data Peano = zero | succ Peano

pleq :: Peano -> Peano -> Bool
pleq zero _ = True
pleq (succ _) zero = False
pleq (succ n) (succ m) = pleq n m


padd :: Peano -> Peano -> Peano
padd zero m = m
padd (succ n) m = succ (padd n m)