.
                                      V
                              i      i o       i
                           o        l a         o
                          l           V            l
                         a          i   o           a
                        V          l    a           V
                         i           V   i            i
                         o           o  l            o
                           l            a            l
                              a      ­  V        a
                                        V
                                        
                                        
                       ­                 
        .