.
                                        B
                             a      a  n           a
                         n          q  u             n
                        q            e t                q
                      u               B                   u
                      e                a                    e
                      t                 n                     t
                     B              q    u                 B
                      a            e        t                a
                       n           B      a               n
                        q            n    q             q
                          u             u              u
                              e          e           e
                                          t