.

                                     B
                             i      i  t      i
                          t         t  e        t
                        t             r             t
                       e             s               e
                      r             w                r
                      s           e    e              s
                     w          t      B            w
                      e           i     t              e
                       e             t                 e
                         t            e              t
                           B         r           B
                              i       s          i
                                 t    w     t
                                       e
                                       e
                                       t