.

                                      F
                              o    o   o     o
                           o       l    F        o
                          l           o              l
                        F            o                F
                       o             l                  o
                       o            F  o              o
                        l           o    l              l
                         F          F  o             F
                          o          o l            o
                            o          F          o
                               l        o       l
                                        o
                                        l