The great secret that all old people share is that you really haven't changed in seventy or eighty years. Your body changes, but you don't change at all. And that, of course, causes great confusion.

Feelings are the subjective aspect of mental processes.

The environment shapes behavior through the mechanism of reinforcement.

数学不是观赏性运动——你必须参与其中才能欣赏它的美。

A building must be true to itself.

在数学中，没有捷径可走。