.
                                    A
                         ­   w   w  e    w
                          e       s   o        e
                       s          m  e          s
                      o             A               o
                    m              w               m
                    e                e                   e
                   A            s        o             A
                    w          m       e             w
                     e           A       w             e
                      s            e     s              s
                       o              o               o
                         m          m          m
                             e         e        e  
                                       A
                                       w
                                       e