The axiom of Zermelo-Fraenkel set theory which asserts the existence for any sets 
and 
of a set 
having 
and 
as its only elements. 
is called the unordered pair of 
and 
, denoted 
. The axiom may be stated symbolically as
 |
Axiom of the Unordered Pair
See also
Zermelo-Fraenkel Set TheoryExplore with Wolfram|Alpha
References
Itô, K. (Ed.). "Zermelo-Fraenkel Set Theory." §33B in Encyclopedic Dictionary of Mathematics, 2nd ed., Vol. 1. Cambridge, MA: MIT Press, pp. 146-148, 1986.Referenced on Wolfram|Alpha
Axiom of the Unordered PairCite this as:
Weisstein, Eric W. "Axiom of the Unordered Pair." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/AxiomoftheUnorderedPair.html