1  2  3   4  5  6   7  8  9
  +---------+---------+---------+
 1| .  .  . | .  .  . | .  .  . |
 2| /  X  / | /  /  / | /  X  / |
 3| .  .  . | .  .  . | .  .  . |
  +---------+---------+---------+
 4| .  .  . | .  .  . | .  .  . |
 5| X  X  X | /  /  / | /  X  / |
 6| .  .  . | .  .  . | .  .  . |
  +---------+---------+---------+
 7| .  .  . | .  .  . | .  .  . |
 8| X  X  X | /  /  / | X  X  X |
 9| .  .  . | .  .  . | .  .  . |
  +---------+---------+---------+