这是最好的时代，这是最坏的时代。
It was the best of times, it was the worst of times.
"The past is never dead. It's not even past."
Innovation is the only way to break through the bottleneck.
一个问题如果在计算机上可以快速解决，那么它属于P类问题；如果一个解可以快速验证，那么它属于NP类问题。