Sometime later, I will deal with functions of more than one variable, which I will briefly introduce to you, because that may not be a prerequisite but certainly something you will learn and you may use on and off.

再过段时间,我要开始处理多变量函数,到时候我会向你们进行简单介绍,因为那不是必须的,但是你们以后会学到,有时候还能派上用场

耶鲁公开课 - 基础物理课程节选

X So now if we actually introduce the variable X, welcome X. Let's do this again.

现在如果我们引进一个变量，欢迎你，X，让我们再做一次。

哈佛公开课 - 计算机科学课程节选