我已经履行了我的职责。我证明了庞加莱猜想，我在数学上没有什么可做的了。

The concept of legal obligation is central to the understanding of law.

We are so accustomed to disguise ourselves to others that in the end we become disguised to ourselves.

实现明天的唯一限制是我们今天的疑虑。

最好的领导方式是展现脆弱。