.

                                     C
                             a     a t       a
                           t        C a         t
                         C           t             C
                        a            C              a
         ­               t          a     t            t
                        C         C    a           C
                         a         t    C          a
                           t         a  t          t
                              C      C       C
                                       A
                                       T