组合数学就像是不用实际计数的计数艺术。
Combinatorics is like the art of counting without actually counting.
The world is a book, and those who do not travel read only one page.
记忆是一件棘手的事情;它既可以是祝福,也可以是诅咒。
纠正一个错误与建立一个新的真理或事实同样有益,有时甚至更好。
Every frame counts, every second matters.