00后大学生：接受函数序偶定义，赢在起跑线上

        现在幸运的是，你们用指尖一点，Keisler教授撰写的“ElementaryCalculus”，等待数秒钟，电子版教材就会飘然而至。
该书第6页，Keisler教授就给出当代布尔巴基学派的函数序偶定义，让你赢在学习微积分的起跑线上。

        感言：互联网大课堂，是你们的学习微积分的好地方。你们的微积分老师就是Keisler教授（现年82岁）开口叫老师吧！。

DEFINITION

        A real fimctionof one variable is a set f of ordered pairs of rea/numbers such that for everyrea/number a one of the following two things happens:

        (i) There isexactly one real number b for which the ordered pair (a, b) is a member of f.In this case we say that f(a) is defined and we write f(a) = b. The number b iscalled the value off at a.

        (ii) There is norea/number b for which the ordered pair (a, b) is a member of f. In this casewe say that f(a) is undefined.

        Thus f(a) = b means that the ordered pair (a, b) is an element of f（函数）.

袁萌  6月17日