NP完全性的概念为理解问题的复杂性提供了一个强大的工具。
创新不是发明全新的东西，而是改进已经存在的东西。
The world is indeed full of peril, and in it there are many dark places; but still there is much that is fair, and though in all lands love is now mingled with grief, it grows perhaps the greater.
One of my primary objects is to form the tools so the tools themselves shall fashion the work and give to every part its just proportion.