极限的ε-Ｎ定义 ,术语抽象 ,符号陌生 ,其中的辩证关系不易搞清 ,学生会提出的一系列问题 :描述性定义简单明白 ,为什么要搞个ε-Ｎ定义 ?它与描述性定义有什么不同 ?数学家怎么会想出这种“古怪而讨厌”的定义 ?正如Ｒ·柯朗与Ｈ·罗宾所说 :“初次遇到它时暂时不理解是不足 The definition of the limit ε-N, the abstraction of terms, the unfamiliarity of symbols, the dialectical relationship among them is not easy to figure out, and a series of questions raised by the Student Union: The descriptive definition is simple and clear, why should we define ε-N? What is the definition of descriptive definition? How does a mathematician come up with this definition of “weird and hateful?” As R. Coron and H. Robin say: "It is not sufficient to understand it for the first time when it is encountered.