现在,集合的概念已经普遍为大家知晓。我们知道,线段可以看成是一条直线上的一些点组成的集合,圆形(包括内部)可以看成是一个平面上的点组成的集合,立方体可以看成是空间内的一些点组成的集合。线段的长度是一个数,既然线段可以看成点的集合,那么长度这个数,和这个集合应该有关系了。什么关系?有一条线段(集合),就有一个数(长度)和它对应。可以认为这之间是一个映射,或者是一一对应的函数关系。这就有点奇怪了!我们知道,函数的自变 The concept of collections is now generally known. We know that a line segment can be thought of as a collection of points on a straight line. A circle (including the interior) can be thought of as a set of points on a plane. A cube can be thought of as a collection of points in space . The length of a line segment is a number, since the line segment can be seen as a collection of points, then the length of this number, and this collection should have a relationship. What is the relationship? There is a line (collection), there is a number (length) and it corresponds. Can think of as a mapping between this, or one by one corresponding function. This is a bit strange! We know that the function of self-change