# ordered pair

or·dered pairnoun

A pair of numbers that come in a specific order and are usually written in parentheses, such as (3, 5).

## ordered-pair

Noun

(*plural* ordered pairs)

- (set theory) An object containing exactly two elements in a fixed order, so that, when the elements are different, exchanging them gives a different object. Notation: (a, b)
*or*.- If an
**ordered pair**were defined (in terms of sets) as then the "first element" of an ordered pair*S*could be defined as CAR(S) where CAR(S) =*x*if and only if . Likewise, the "second element" of*S*could be defined as CDR(S) where CDR(S) =*x*if and only if . If the two elements happened to be equal, then the ordered pair would still have cardinality two as would be naturally expected.

- If an