Purity, which is the absence of impurity, is a prerequisite for access to the holy or for holy status.

纯洁，不纯的反义词，是接近神圣或达到神圣状态的先决条件。

耶鲁公开课 - 旧约导论课程节选

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