F ncsub(seq, s = 0)
   I seq.empty
      R I s >= 3 {[[Int]()]} E [[Int]]()
   E
      V x = seq[0.<1]
      V xs = seq[1..]
      V p2 = s % 2
      V p1 = !p2
      R ncsub(xs, s + p1).map(ys -> @x + ys) [+] ncsub(xs, s + p2)

print(ncsub(Array(1..3)))
print(ncsub(Array(1..4)))
print(ncsub(Array(1..5)))