.
                                    Cat
                               a   Cat   C
                             t      Cat      a
                           C      C   a        t
                          a       t     C        C
                          t       a       t        a
                           C      C     a        t
                            a       t   C        C
                               t       a        a
                                 C    t      t
                                       a
                                        t