.
                                       B
                              e      e a       e
                           a          s t           a
                         s             B              s
                        B              e               B
                        e            a   s             e
                         a           t   B            a
                          s           e  a            s
                           t           s  t           t
                             B        B e        B
                               e        a         e
                                 a      s       a
                                    s    T    s