.
                                    Nut
                               C   C  r  C
                              r     a  c    r
                            a       k  e      a
                           c           r          c
                          k           N           k
                        e             u             e
                       r               t               r
                     N               c r              N
                    u                a c               u
                    t                k   e                t
                    c              r     N               c
                     r            u        t              r
                      a   ­         c       r             a
                       c             a    c             c
                          k           k e           k
                              e         r           e
                                     r  N  r
                                         u
                                          t