data Natx a = Zx | Sx a (Natx a)

fun1 :: Natx Int -> (Natx Int, Int)

fun1 x = case x of

Zx -> (Zx, 0)

Sx n k -> (Sx n (fst (fun1 k)), n * (fun2 k) - 0)

fun2 :: Natx Int -> Int

fun2 x = case x of

Zx -> 0

Sx n k -> (snd (fun1 k)) + n