The definition of a good mathematical problem is the mathematics it generates rather than the problem itself.
写书就像冒险。一开始它是玩具和娱乐。然后她成了你的情妇。然后是你的主人。然后变成一个暴君。最后你终于认命的时候,它死了,然后给拖到外面游街。
I have a dream that one day this nation will rise up and live out the true meaning of its creed.