F s_permutations(seq)
   V items = [[Int]()]
   L(j) seq
      [[Int]] new_items
      L(item) items
         I L.index % 2
            new_items [+]= (0..item.len).map(i -> @item[0 .< i] [+] [@j] [+] @item[i..])
         E
            new_items [+]= (item.len..0).step(-1).map(i -> @item[0 .< i] [+] [@j] [+] @item[i..])
      items = new_items

   R enumerate(items).map((i, item) -> (item, I i % 2 {-1} E 1))

L(n) (3, 4)
   print(‘Permutations and sign of #. items’.format(n))
   L(perm, sgn) s_permutations(Array(0 .< n))
      print(‘Perm: #. Sign: #2’.format(perm, sgn))
   print()