.
                                    N
                           i        ir        i
                         r         va         r
                       v           n             v
                      a            a               a
                     N           N  i             N
                     i             r   v              i
                     r             a  n              r
                     v             a N              v
                      a             i r              a
                        n            v            n
                            a        a        a
                                      n
                                      a