.
                                    Z
                              o   oo    o
                            o     Zo       o
                          Z       oZ         Z
                         o         o            o
                         o       o    Z        o
                          Z      o     o        Z
                          o      Z     o       o
                           o      o   Z       o
                             Z     o o      Z
                                o    Z     o
                                  o  o  o
                                       o