Definition:Unordered Tuple

Definition
An unordered tuple is a small class in ZF set theory that contains a finite number of elements.

It is written using roster notation and is denoted:
 * $\left\{ {a_1, a_2, \ldots, a_n}\right\}$

that is:
 * $\left\{ {a_1, a_2, \ldots, a_n}\right\} = \left\{ {x : x = a_1 \lor x = a_2 \lor \dots \lor x = a_n}\right\}$