The symbol belongs to: ∈

Inclusion: For two sets A and B, if any element in set A is an element in set B, we say that these two sets have an inclusion relationship, and that set A is a subset of set B ... Write: A? B (or b? A) pronounced "A is contained in B" ("B contains A"). At this point, a belongs to B.

The implication of truth is proper subset. If you set one? B, but there is element X∈B, and element X does not belong to set A. We call set A proper subset of set B. That is to say, if all elements of set A are elements of set B at the same time, A is called a subset of B. If there are elements in b, but not in A, and A is a subset of B, A is called proper subset of B.

Extended data:

Intersection and union

Intersection definition: a set consisting of the same elements belonging to A and B, marked as A ∩ B.

(or B∩A), pronounced as "A across B" (or "B across A"), that is, A∩B={x|x∈A, x∈B}, as shown in the right figure. Note that the intersection is getting less and less. If a contains b, then A∩B=B, A∪B=A? .

Union definition: a set consisting of all elements belonging to set A or set B, marked as A∪B (or B∪A) and pronounced as "A and B" (or B and A), that is, A∪B={x|x∈A, or X ∈ B, pay attention to the more union.

supplementary set

Complement sets can be divided into relative complement sets and absolute complement sets.

Definition of relative complement set: A set composed of elements belonging to A but not to B, called B's relative complement set about A, and denoted as A-B or A\B, that is, A-B={x|x∈A, and X? B'}？ .

Definition of absolute complement set: A's relative complement set about complete set U is called A's absolute complement set, and it is denoted as A' or? U(A) or ~ a. There is u' = φ; φ' = U？ .