.
                                    C
                         ­  o      o w        o
                        w         Co           w
                       C            w              C
                      o           C   o              o
                    w         w        C           w
                     C         o         w           C
                       o         C      o           o
                         w          w           w
                                 c           c
                                       O
                                       w