 as follows.                                                         f              i                              n                +                0                                      -                          f              i              n                                            Δ            ⁢                          xe0x00x00                        ⁢            t                          =                                            f                              i                +                0                                            n                +                0                                      -                          0              ⁢                              f                i                                  n                  +                  0                                                      +                          f                              i                -                0                                            n                +                0                                                          Δ            ⁢                          xe0x00x00                        ⁢                          x              0                                                          (        0        )             