.
              
                                      B
                              o     o x     o
                            x       B 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
                                         o
                                         x