.
                                     q
                            u      u i      u
                           i        d d         i
                         d         i  t           d
                        d           y              d
                        i          q    u           i
                        t          i      d          t
        ­                 y        d      i          y
                          q         t   y         q
                            u         q          u
                                i      ui       i
                                        d
                     ­                    i
                                         t
                                        y