Example A={ 1, 2}, B={ 1, 2, 3}

Then 1 ∈ A, 2 ∈ A, 3 ∈ b.

Answer? B

Contained in:, horizontally contained in,? The following ≠ is really included in.

Answer? B means that all elements of a belong to B.

Answer? B stands for a? B but a ≠ B.

Attribution is the relationship between elements and sets. For example, the element A belongs to the set A and is marked as A ∈ A.

Attribution symbol: ∈, used between elements and sets.

Points are generally represented by lowercase letters, and sets are represented by uppercase letters!