A set of specified objects are combined into a set, which is called a set for short, and each object in the set is called an element of the set.

Subset: Set a and B. If A is a subset of B, A can be equal to B. If A is proper subset of B, A cannot be equal to B..

Let me give you an example. If A = {1, 2,3}, B = {1, 2,3}, it can only be said that A is a subset of B, and it cannot be said that A is the proper subset of B. If A = {1, 2,3}, B = {

Complement set: Generally speaking, let S be a set, A be a subset of S, and the set of all elements in S that do not belong to A is called the complement set of subset A in S. 。

Complete works: Complete works are the largest collection, and generally a topic will specify a complete works. In general, the set of all rational numbers is the complete set by default.