.
                                     G
                             o    o  o    o
                          o       d  G      o
                       d          G  o         d
                     N             G              N
                     i               o                 i
                   g                o                   g
                   h                d                    h
                  t      ­         N      i                  t
                 G             g          h               G
                  o             t           N              o
                   o             i          g              o
                     d             h     t               d
                      N              G                N
       ­                  i             o              i
                           g          o           g
                             h        d        h
                                 t     N     t
                                        i
                     ­                   g
                                        h
  ­                                      t