因果关系的阶梯有三个梯级：观察、行动和想象。

Mathematics is a universal language that transcends cultural and linguistic barriers.

释义：看见一片落叶，就知道一年内的时间将要到头了。通过细微的迹象，可以预料到整个形势的发展趋向与结果。

A proof that P = NP would have profound implications for mathematics, cryptography, and algorithm design.

我不是模特。我只是一个喜欢打扮的女孩。