.
                                   m
                            u    u f    u
                         f        f m       f
                       f          u f          f
                     m          f m           m
                    u             u                u
                   f                f                  f
                  f        ­         f                   f
                 m                m                 m
                 u                 uf                   u
                 f                f   m                 f
                 f               u      f                 f
                 m             f      m              m
                  u              u     f               u
                     f             f  m             f
                           f         u        f
                                      f
              ­                        f