In modern mathematics set theory, elements are every object that constitutes a set. In other words, a set consists of elements, and each object that makes up a set is called an element that makes up a set. For example, 1, 2,3 in the set {1, 2,3} are all elements of the set.

There are only two possibilities between element a and a given set a:

1, A belongs to the set A, which is expressed as an element of the set A and recorded as A ∈ A

2.A does not belong to the set A, which means that A is not an element of the set A, and it is recorded as A? Answer.

Extended data

Properties of collection elements

1. Certainty: Every object can determine whether it is an element of a set. Without certainty, it cannot be a set. For example, "tall classmates" and "small numbers" cannot form a set. This property is mainly used to judge whether a set can constitute a set.

2. Relevance: Any two elements in the set are different objects. If written as {1, 1, 2}, it is equivalent to {1, 2}. Being different from each other makes the elements in the collection not repeat. When two identical objects are in the same set, they can only be counted as an element of this set.

3. Disorder: {a, b, c}{c, b, a} are the same set.

4. Purity: The purity of the so-called set is represented by an example. Set a = {x | x

5, integrity: still use the above example, all in line with X.

In addition to the above properties, a set has the following properties: if A is contained in B, then A∩B=A, and a ∪ b = b

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