.
                                      F
                               o    o o    o
                             o      d F      o
                            d      o o        d
                           F         d           F
                           o       F  o         o
                            o      o   d        o
                             d      F  o       d
                               F       o       F
                                  o    d     o
                                     o      o
                                         d