屋顶上的天空，如此蔚蓝，如此宁静！

开玩笑是件严肃的事情。

The only real mistake is the one from which we learn nothing.

To enjoy freedom we have to control ourselves.

The human heart is a complex and often contradictory thing.

心理学的方法必须像自然科学的方法一样精确。

The most important thing is to have a vision of what you want to do and then to have the persistence to carry it out.

在数学中，提出问题的艺术必须比解决问题更有价值。