A set containing exactly one element is called a singleton.
Question: Is there a name for a set containing exactly two elements?
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max_zorn
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2Occasionally it is called an unordered pair. – Michael Hardy Apr 20 '18 at 23:47
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5I've heard "doubleton" used a couple times, but I've never seen it in print. "Pair" I think might be confusing on its own since it suggests ordered pair, so "unordered pair" is perfectly reasonable. – Noah Schweber Apr 20 '18 at 23:50
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@NoahSchweber THANKS - it does show up a few times on Math Reviews, so unless something else pops up, I will use it. – max_zorn Apr 20 '18 at 23:51
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1Dont forget about tripletons and dodecatons and all of the other ones. Know your greek and latin prefixes. – CogitoErgoCogitoSum Apr 21 '18 at 00:48
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What about $k$-set for $k \ge 1$? – StefanH Aug 25 '23 at 19:08