proc dif(s: seq[int]): seq[int] =
  result = newSeq[int](s.len-1)
  for i in 0..<s.high:
    result[i] = s[i+1] - s[i]

proc difn(s: seq[int]; n: int): seq[int] =
  if n > 0: difn(dif(s), n-1)
  else: s

const s = @[90, 47, 58, 29, 22, 32, 55, 5, 55, 73]
echo difn(s, 0)
echo difn(s, 1)
echo difn(s, 2)