1: Not, or, and are all derived from the set. Therefore, to understand these relative words, we must

Let's talk at the rally.

2. In fact, the most fundamental set should be a set of points. Description of the rest of the set:

Such as enumeration, explanation, description, etc. Is to show which points belong to this set.

For example, the set A={ 1, 2,3} This is an enumeration method, which clearly states that the point 1, 2,3 belongs to the set A, and the set only contains these three elements, and all other elements do not belong to this set.

Description: Set a = {x | 1

3. With the help of the concept of set, we will discuss the relationship between two or more sets. This leads to the concepts of intersection, union and complement. At the same time, we will also discuss another problem, how to express the relationship between sets, thus leading to the concepts of not, and, or.

4. The concept of "non" involves not only set A itself, but also complete set Q. Only when both of them are clear can we discuss the non-existence of set A. ..

The definition of "Fei" is that the Fei of set A is the set of all elements in complete set Q that do not belong to set A, for example, A={ 1, 2,3}, and complete set Q={ all positive integers}, then

"Non-a" = the set of all elements in all positive integers that are not 1, 2,3 = {4,5,6, ...}

What you should pay attention to is that the process of seeking "non-A" here is completely in line with the definition.

Therefore, it is important to understand the definition. Only when the definition is clear can we understand the content derived from it.

The definition of "OR" is: A or B refers to the set of all elements belonging to set A or set B. "OR" means "one of the two".

An element A belongs to a set (A or B), which can be divided into three situations.

Item 1: Element A belongs to set A, but not to set B.

Type 2: element a belongs to set b, but not to set a.

Type 3: Element A belongs to both set A and set B..

The definition of "harmony" is: A and B refer to the set of all elements belonging to both sets A and B. "Harmony" means "both".

For example, if A = {1, 2,3} and B = {2 2,4,5}, then A and B represent the set of all elements that are both A and B, so the result is {2}, because only element 2 is the element of sets A and B.

5. The essence of discussing the relationship between sets is to discuss the relationship between elements of sets.

You can find that the definitions of so-called or, and non are all defined from the perspective of elements.

6. Mathematics comes from practical problems, not empty. Learning math is more important.

Under what circumstances and how did this senior mathematician produce his theory, why did he define the concept like this and why did he deduce it like this? Only in this way can you find the beauty and loopholes in his theory.

7: If you are interested in mathematics, if time permits, I recommend you to read A Brief History of Mathematics.