.
                                       A
                                r    r   t     r
                            t        A   r       t
                         A            t             A
                        r             A                r
                       t               r                  t
                       A           t      A            A
                       r           r        t             r
                        t            A     r             t
                         A              t              A
                           r            A            r
                               t         r        t
                                         t
                                         A
                                         r
                                         t