.
                                   B
                        o       o   x     o
                     x          B   o         x
                   B              x              B
                  o               B                 o
                 x                 o                  x
                B                  x                   B
                o              B       o               o
                x              x        B              x
                B              o        x              B
                 o               B     o              o
                   x                x                x
                      B            B             B
                          o         o         o
                              x     x     x