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攻击我很厉害我也回敬得很厉害,攻击我很轻微我也回敬得很轻微。 
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。
容易得到的东西,是靠不住的;轻易许下的诺言,不值得信赖。
The future of life on Earth depends on our ability to take action. Many individuals are doing what they can, but real success can only come if there is a change in our societies and our economics and in our politics.