.

                                      S
                             p     p   i     p
                          i         c   e          i
                        c             S               c
                      e               p                e
                      S               i                  S
                      p               c                  p
                      i             e     S              i
                       c           p       i            c
                        e           c     e            e
                         S           S   p           S
                           p           i              p
                              i          c           i
                                c       e        c
                                   e    S     e
                                         p
                                         i
                                         c
                                         e