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。
The teacher must believe in the potential of his students.
The best moments in our lives are not the passive, receptive, relaxing times... The best moments usually occur if a person's body or mind is stretched to its limits in a voluntary effort to accomplish something difficult and worthwhile.
The truth is rarely pure and never simple.