.

                                    b
                        ­    l      l  o      l
                         o        o  d         o
                       o            h             o
                      d             o               d
                     h              u                h
                     o              n                 o
                     u         d        b           u
                      n         l        o           n
                      d           o    d           d
                        b            h              b
                          l            o            l
                           o          u          o
                              o       n       o
                                       d