F ack2(m, n) -> Int
   R I m == 0 {(n + 1)
 } E I m == 1 {(n + 2)
 } E I m == 2 {(2 * n + 3)
 } E I m == 3 {(8 * (2 ^ n - 1) + 5)
 } E I n == 0 {ack2(m - 1, 1)
 } E ack2(m - 1, ack2(m, n - 1))

print(ack2(0, 0))
print(ack2(3, 4))
print(ack2(4, 1))