In mathematics, an ordered pair (a, b) is a pair of objects.
The order in which the objects appear in the pair is significant:
the ordered pair (a, b) is different from the ordered pair (b, a) unless a = b.
Ordered pairs are also called 2-tuples, or sequences
(sometimes, lists in a computer science context) of length 2.
Ordered pairs of scalars are sometimes called 2-dimensional vectors.
(Technically, this is an abuse of notation since an ordered pair need not be
an element of a vector space.)
The entries of an ordered pair can be other ordered pairs,
enabling the recursive definition of ordered n-tuples
(ordered lists of n objects).
For example, the ordered triple (a,b,c) can be defined as (a, (b,c)),
i.e., as one pair nested in another.
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