.
                                      C
                             u      u n       u
                          n         t  C          n
                          t            u              t
                         C            n               C
                         u             t               u
                         n         C     u           n
                          t         n      t           t
                           C        C    u          C
                             u       n   t          u
                                n       C         n
                                   t     u       t
                                          n
                                          t