And in fact, one of the lessons you may already be realizing with P sets is that things seem to take twice, three times, four times longer than you actually might think.

从习题集中你可能已经得出的一个教训就是,程序所花的实际时间往往是你开始以为的两倍，三倍，四倍甚至更长。

哈佛公开课 - 计算机科学课程节选

It varies with the square of distance so it goes - in order to go twice as far it takes four times as long.

速度是与距离的平方正相关的--,如果要扩散两倍的距离要多花四倍的时间

耶鲁公开课 - 生物医学工程探索课程节选