.
                                     free
                                 r  free  f
                               e    free    r
                              e     free     e
                             f          f          e
                            r           r           f
                          e            e             r
                         e             e              e
                        f            fr ee      ­      e
                       r          fr      ee           f
                       e         fr       ee            r
                      e           fr      ee             e
                      f            fr     ee              e
                       r            fr  ee               f
                        e            free               r
                         e              f                 e
                            f            r              e
                                r  ­      e           f
                                     e   e     r
                                          e
                   ­                       e