[next] [prev] [prev-tail] [tail] [up]
{ 10, 11, 12, 15, 16, 17, 18, 20, 21 }
{ 1, 2, 3, 4, 19, 23, 24, 25, 26 }
{ }
{ 5, 6, 7, 8, 9, 22, 27 }
[next] [prev] [prev-tail] [front] [up]