.
                                      Y
                       ­      o     o   u      o
                          u        c   n         u
                        c              a               c
                       a              N                 a
                      n                e                  n
   ­                  N                v                   N
                      e            e         r             e
                      v            b        e             v
                       e            t       o             e  
                         r               o                r
                          b              t    ­           b
                            e            h            e
       ­                        t          i           t
                                 o       n       o
                                     o   o    o
                                           r
                                           t
                                           o
                                           o
                                           r
                                           i
                                           c
                                           h