.

                                    Tr
                           C      a  f       C
                         o        f   i          o
                        u           c             u
                       r            T                r
                      t              r                  t
                     C              a                  C
                    o            f       f               o
                    u           i        c               u
                    r             T     r                r
                      t                a                  t
                       C               f                C
                          o            f              o
                             u         i           u
                                r      c       r
                                     t     t