$$ o(x^m)\pm o(x^n) = o(x^n) \quad (m > n) $$

$$ x^m \cdot o(x^n) = o(x^{m+n}) $$

$$ o(x^m) / o(x^n) = 0 \quad (m > n) $$

$$ 有界函数f(x) \cdot o(x^n)=o(x^n) $$

$$ k \cdot o(x^n) = o(x^n) $$