故仓无备粟，不可以待凶饥；库无备兵，虽有义不能征无义；城郭不备全，不可以自守；心无备虑，不可以应卒。
仓库里没有储备的谷物，不可以应付凶饥之年；兵库不准备兵器，没有足够的实力，即使站在正义的一方也无法征讨无义之人，实力是维护正义的强有力的保障；城郭防守不完全，则不能守护自己；没有居安思危的心理，不可应付突发事件。
The true spirit of delight, the exaltation, the sense of being more than Man, which is the touchstone of the highest excellence, is to be found in mathematics as surely as in poetry.
Sometimes silence between the notes is just as important as the notes themselves.
过去总是紧张的，未来是完美的。
The future is already here — it's just not very evenly distributed.
学习数学的最好方法就是去做数学。