NP中的每个问题都可以归约为可满足性问题，这是计算复杂性理论的基石。
Every problem in NP can be reduced to the satisfiability problem, which is the cornerstone of computational complexity theory.
The man who writes about himself and his own time is the only man who writes about all people and about all time.
The best stories don’t talk down to children—they invite them in.