Element

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An element, also called a member, is an object contained within a set or class.

$A=\{1,\,2,\,3,\,4\}$ means set $A$ contains the elements 1, 2, 3 and 4.

To show that an element is contained within a set, the $\in$ symbol is used. If $A=\{2,\,3\}$ , then $2\in A$ .

The opposite of this would be $\notin$ , which means the element is not contained within the set.

Elements Within Elements

Elements can also be sets. For example, $B = \{1,\,2,\,\{3,\,4\}\}$ . The elements of $B$ are not 1, 2, 3, and 4. Actually, there are only three elements of $B$ : $1$ , $2$ , and the set $\{3,\,4\}$ .

Cardinality

The amount of elements in a set is known as cardinality. If $C=\{1,\,2,\,3\}$ , then the cardinality of $C$ is $3$ . Informally, cardinality is the size of a set.

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Element

Elements Within Elements

Cardinality

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