_______  _______  _______  _______
| | | |  | | | |  | | | |  | | | |
-------  -------  -------  -------
| | | x  | | | |  | | | x  | x | |
-------  -------  -------  -------
| | | |  | | | x  | | | |  | | x |
-------  -------  -------  -------
| | | |  | | | |  | | | |  | | | |
-------  -------  -------  -------
| | | |  | | | |  | | | |  | | | x
-------  -------  -------  -------
  d         u        d     u-ud-


   -------  -------  -------  -------  -------
   | | | |  | | | |  | x | x  | x | |  | x | x
   -------  -------  -------  -------  -------
10 | | | x  | | | |  | | x |  | | x x  | | x |
   -------  -------  -------  -------  -------
   | x | |  | x | |  | | | |  | | | |  | | | |
   -------  -------  -------  -------  -------
   | | x |  | | x x  | | | |  | | | |  | | | |
   -------  -------  -------  -------  -------
     d-        d        u     u-ud       u