.

                                     I
                               n   n e    n
                            e       f f         e
                          f           a            f
                         f            b              f
                        a             l               a
                        b            e                b
                       l            I     n             l
                       e          e       f            e
                       I            f      a            I
                        n           b    l            n
                          e           e  I           e
                            f           n           f
                               f        e        f
                                         f
                                         f
                                         a
                                         b
                                         l
                                         e