.

                                    A
                        ­     r     rt       r
                           t       Ar         t
                         A          t            A
                        r          A  r           r
           ­             t         t     A           t
                       A        r       t          A
                         r        A     r          r
                          t         t    A         t
                            A       r  t        A
                               r      A       r
                                   t   r    t
                                        t