# 2-Tuple

A 2-Tuple is a tuple with 2 Members.

**AKA:**Ordered Pair, Ordered 2-Tuple.**Context:**- It can be represented as <x,y> (or as the ordered set {x, {y}}).
- It can be captured in a 2-Tuple Record.
- …

**Example(s):**- A Multiset, composed of a set and a Frequency Function.
- A Metric Space, composed of a Point Set and a Distance Function.
- E.g. (
*10,Clubs*) a Symbol on a Card from a Card Draw Experiment.

**See:**1-Tuple, 3-Tuple, 4-Tuple.

## References

- http://www.isi.edu/~hobbs/bgt-sequences.text
- The distinguishing feature of ordered pairs, or simply "pairs", is that they have a first and a second element.
`(1)`

- The distinguishing feature of ordered pairs, or simply "pairs", is that they have a first and a second element.

(forall (p)
(if (pair p)
(exists (x y) (and (first x p)(second y p)))))

```
```

- We could define pairs in the traditional way in set theoretic terms. The pair <x,y> is defined as the set {x, {y}}. This is certainly a model of the axioms involving "pair", but it would be pedantic to call this the definition.