A pair is usually an n-tuple for n=2n = 2, that is an ordered pair. Such a pair is a term of product type, an element of a Cartesian product, a generalized element of a product object, etc.

But a pair may also be an unordered pair. The existence of these is a basic axiom of ZFC and its variations, the axiom of pairing.

Revised on April 6, 2017 00:22:09 by Toby Bartels (