.

                                    B
                           u    u   n      u
                        n       n   y         n
                      n            B              n
                     y             u                 y
                    B              n                 B
                   u            n    y              u
                   n           B      u             n
                    n           n    n             n
                     y            y  B             y
                       B           u              B
                          u        n           u
                             n     n       n
                                     y