已知一个有理数类Zrf_Ratio，实现如下的操作符重载形式：

friend std::ostream& operator< (std::ostream&, const zrf_Ratio&)

friend std::istream& operator>>(std::istream&, zrf_Ratio&)

friend bool operator==(const zrf_Ratio&, const zrf_Ratio&)

friend bool operator<(const zrf_Ratio&, const zrf_Ratio&)

-Known type of a rational number Zrf_Ratio, the achievement of the following form of operator overloading: friend std:: ostream &　operator < < (std:: ostream & , const zrf_Ratio & )　friend std:: istream &　operator> >　(std:: istream & , zrf_Ratio & )　friend bool operator == (const zrf_Ratio & , const zrf_Ratio & )　friend bool operator < (const zrf_Ratio & , const zrf_Ratio & )