.
                                     C
                              u    u p   u
                            p      C a       p
                          C        k e         C
                        a           C             a
                      k             a               k
                     e              k                e
                    C          ­     e                 C
                   u             C   u               u
                   p            p     C               p
                   C            a      k               C
                   a             e     C               a
                    k              u  p               k
                     e                C               e
                       C              u             C
                          u           p          u
                              p       C      p
                                        a
              ­                          k
                                     ­   e