.

                                       M
                               o     oo       o
                             o        N           o
                           n          M            n
                          M        o   o           M  
                          o         n   M           o
                          o         o     o           o
                           n        n   M          n
                            M       o   o         M
                              o       n M        o
                                o       o         o
                                    n   o    n
                                          n