Complement set, because B is not included in A, it cannot be complemented.
If B={ 1, 2,3}? B's complement to A is {4,5}? B-A= empty set
Complement set generally refers to absolute complement set, that is, generally let S be a set, A be a subset of S, and the set composed of all elements that do not belong to A in S is called absolute complement set of subset A in S. In other branches of set theory and mathematics, complement set has two definitions: relative complement set and absolute complement set.
Schematic diagram of relative complement set (difference set)
In other branches of set theory and mathematics, complementary sets have two definitions: relative complementary sets and absolute complementary sets.
1, relative complement set
If a? What about B. It's a set, and then a. In b? A relative complement set in is a set whose elements belong to B but not to A, B? -A？ = {x| x∈B and x? Answer.?
2. Absolute complement set
Given a complete set u, there is one? U, then the relative complement set of A in U is called the absolute complement set of A (or simply the complement set). UA .？
Note: To learn the concept of complement, we must first understand the relativity of complete works and the symbols of complement. UA has three meanings:
1, a is a subset of u, that is, a? u；
2、? UA stands for a set, and? UA？ u；
3、? UA is a set of all elements in U that do not belong to A. UA and A have no common elements, and the elements in U are distributed in these two sets.
Generally speaking, remember that A and B are two sets, then the set composed of all elements belonging to A but not to B is called set A minus set B (or the difference between set A and set B). Similarly, for sets a and b, we take the set x∣x∈A, and x? B is called the difference set of A and B. Tracing images is an added function in Dreamweaver 2.0, but we still need to mention it when introducing Dreamweaver 4.0.
The difference set describes all the non-overlapping areas of the object and makes the overlapping areas transparent. A good way to understand a strange thing well is to compare it with something similar but familiar.