.
                                   m
                          b      bfp       b
                       f         mbf         f  
                      P         pmb          p
                      ~          f  p            ~­
                      m      m     b          m
                       b       f        p         b
                        f        m    b         f
                         P        f   p         p
                           ~        m         ~
                             ~      b        ~
                                      f
       ­                               p