Mathematics is not a deductive science—that's a cliché. When you try to prove a theorem, you don't just list the hypotheses and then start to reason. What you do is trial and error, experimentation, guesswork.

心灵是自己的地方，在那里可以把地狱变成天堂，把天堂变成地狱。

建筑是协调形式与功能的艺术。