.

                                    S
                             i     i  d    i
                         d       e  c         d
                       e           h              e
                      c             i                 c
                    h              c                  h
                    i               k                    i
                   c             S     i                 c
                   k             d    e                k
                    S             c   h               S
                      i             i  c              i
                        d            k            d
                             e       S         e
                                       i
                                       d
                                       e