But the kind of exercise we did last time is a useful exercise for those of you who are Econ majors.

但是我们上节课做的练习,对经济学专业的同学是非常有用的

耶鲁公开课 - 博弈论课程节选

So you can scroll back through your history, which is also useful for time's sake.

所以我们可以滚回到我们的历史记录，这个可以节约我们的时间。

哈佛公开课 - 计算机科学课程节选