上海復旦大學國際問題研究院教授宋國友此前向官媒公號《玉淵譚天》強調，制裁日本的效力不只體現在經濟損失，更重要的是震懾日本。他說，中方公開點名制裁，就是明確信號，「意味任何繼續與其合作的企業和個人，都必須認真評估被中國制裁的現實風險。」
The fundamental group of \(X\) at \(x_0\) is \[\pi_1(X, x_0) \;:=\; \bigl\{[\gamma] \mid \gamma \text{ is a loop based at } x_0\bigr\}\] equipped with the group operation of concatenation: \[[\gamma] \cdot [\delta] := [\gamma * \delta], \qquad (\gamma * \delta)(s) := \begin{cases} \gamma(2s) & s \in [0,\tfrac{1}{2}] \\ \delta(2s-1) & s \in [\tfrac{1}{2},1] \end{cases}\] The identity element is the class of the constant loop \([c_{x_0}]\), and the inverse of \([\gamma]\) is \([\bar\gamma]\) where \(\bar\gamma(s) := \gamma(1-s)\).
。51吃瓜对此有专业解读
Pretty vs. Ugly Errors
Фото: Elizabeth Frantz / Reuters
On an implementation level, the target compatibility mechanism and