∑ "is a symbol in mathematics, which is pronounced as" belonging ".

If a is an element of set A, it is said that A belongs to set A, marked as A ∈ A; If a is not an element in set a, say that a does not belong to set a, and record it as a? Answer.

For example, a represents the set of "all prime numbers in 1~20", so there is 3 ∈ a.

Relational character

For example, = is an equal sign, ≈ is an approximate symbol (that is, approximately equal to), ≠ is an unequal sign, > is a greater than sign,