.
                                      A
                            b       bs        b
                          s         ur           s
                         u          d              u
                        r          A ­  b            r
                        d          s    u         ­   d
                       A          r     d            A
                        b          A    b         ­  b
                         s           s   u            s
                          u            r          ­   u
                            r          d           r
                               d     #!@     d
                                       &%
                                         =