.
                                       N
                            o        os         o
                          s          eN            s
                        e             o               e
                       N             s                 N
                      o               e                  o
                      s            N    o               s
                      e            s     e               e
                       N          N    o             N
                         o          s   e            o
                             s         N           s
                                 e     o       e
                                        s
                                        e