Art of Problem Solving

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


<math>A=\{1,\,2,\,3,\,4\}</math> means set <math>A</math> contains the elements 1, 2, 3 and 4.
<math>A=\{1,\,2,\,3,\,4\}</math> means set <math>A</math> contains the elements 1, 2, 3 and 4.
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Elements can also be sets. For example, <math>B = \{1,\,2,\,\{3,\,4\}\}</math>. The elements of <math>B</math> are not 1, 2, 3, and 4. Actually, there are only three elements of <math>B</math>: <math>1</math>, <math>2</math>, and the set <math>\{3,\,4\}</math>.
Elements can also be sets. For example, <math>B = \{1,\,2,\,\{3,\,4\}\}</math>. The elements of <math>B</math> are not 1, 2, 3, and 4. Actually, there are only three elements of <math>B</math>: <math>1</math>, <math>2</math>, and the set <math>\{3,\,4\}</math>.


=== Cardinality ===
== See Also ==
 
* [[Cardinality]]
The amount of elements in a set is known as [[cardinality]]. If <math>C=\{1,\,2,\,3\}</math>, then the cardinality of <math>C</math> is <math>3</math>. Informally, cardinality is the size of a set.

Revision as of 20:22, 1 November 2006

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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 $\{3,\,4\}$.

See Also