bool operator!=(const Number &lhs, const Number &rhs)
bool operator<=(const Number &lhs, const Number &rhs)
bool operator>=(const Number &lhs, const Number &rhs)
bool operator>(const Number &lhs, const Number &rhs)
ostream & operator<<(ostream &out, const Number &num)
bool operator<(const Number &lhs, const Number &rhs)
bool operator==(const Number &lhs, const Number &rhs)