.
                                      B
                            a       as        a
                           s        ke          s
                          k          t             k
                         C         C   a          C
                         a        s     e          a
                         s        B      a         s
                          e        s     k         e
                           B        e  t          B
                             a        C          a
                               s       a        s
                                  k    s     k
                                        e