.

                                      C
                      ­       h    h   e     h
                           e       r   r        e
                         r            i             r
                        r             e               r
                       i               s                 i
                      e            C     h             e
                      s             -------              s
                      C            e      r             C
                       h            r    i              h
                        e     ­         e                e
                         r              s               r
                           r            C            r
                             i           h          i
                               e        e        e
                                   s    r     s
                                         r
                                         i
                                         e
                                         s