.

                                      Y
                      ­       u      um      u
                          m        my         m
                         m          Y             m
                        y           y   u            y
                        Y         m    m          Y
                         u         y     Y          u
                          m       u    m        m
                           m       m  y        m
                              y         Y          y
                                Y       u        Y
                                    u   M    u