.
                                 Co
                             -   ed  -
                          Co   Co     ed
                        Co      C        Co
                        -          o           -
                    ed          -              ed
             ­      Co            e              Co
                   -              C  o               -
                 ed            e    d             ed
                Co           C       o              Co
                 -              e       d               -
                 ed            C     o              ed
                  Co               e                 Co
                    -                 d               -
                       ed           C           ed
                          Co        o        Co
              ­                ed     -     ed
                                       e
                                       d