.
                                   L
                        i        i   f       i
                     f          e   L          f
                   e              i               e
                  L               f                L
                 i                 e                 i
                 f              L      i              f
                 e             f        e             e
                  L             L    i               L
                    i                f                i
                      f              e             f
                           e        L         e
                                      i
                                      f
                                      e