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Is there a symbol for potential equality? Essentially I'd like to condense:

$$ (a = b) \lor (a \ne b) $$

so that I can express the phrase "a may or may not be equal to b". Apologies if my syntax is not entirely correct; I come from a computer science background.

Jake Petroules
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  • What context would you want to do this in? I would personally use an equals sign with a question mark above it. – Tom Oldfield Dec 07 '12 at 23:50
  • That's what I've usually seen as well - what Tom suggested. – Joe Dec 07 '12 at 23:51
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    What would you like a symbol that carries no information? Or if it should, what kind of information you would like it to have? – dtldarek Dec 07 '12 at 23:53
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    From a logical point of view, $(a=b)\lor (a\ne b)$ is a tautology. One can condense it by saying nothing. – André Nicolas Dec 07 '12 at 23:56
  • True, but I had a case in which I specifically wanted to emphasize that fact by asking whether it was the case that (a = b) or the case that (a ?= b)... unless there is a way to condense THAT? – Jake Petroules Dec 08 '12 at 00:16
  • André, in cases where it might potentially be assumed that $a = b$ or assumed that $a \ne b$ you may want to be explicit in saying that it's not known. Usually the way I phrase the meaning of this needed symbol is "does not necessarily equal." Let's say you're trying to prove the general case for a theorem and find that the theorem is false, even though it works in some specific cases. It helps to be able to make the distinction. – Kyle Delaney Oct 28 '15 at 07:04
  • Perhaps you mean to state that $a$ and $b$ are of the same type, so that it makes sense to ask whether they are equal in the first place? – Toby Bartels Jan 22 '16 at 19:59

2 Answers2

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The most common usage I have seen is

$$a \overset{?}{=} b$$

Usually its context I've seen is before you're trying to prove that they indeed equal or something of that matter.

Joe
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  • No Unicode symbol for a question mark over an equals sign? – Jake Petroules Dec 07 '12 at 23:53
  • Not that I'm aware of. You can define it as a new command if you're going to be using it a lot. Also, \overset allows for other symbols to be used above an equals sign, such as !. \overset and amsmath are preferred over \stackrel{?}{=} I believe. – Joe Dec 07 '12 at 23:55
  • I don't see it often in texts - usually it is not needed, as noted in the comments to the OP's question. I'd definitely say it's more informal. I've seen it in lectures given by my professors, as well as in a few texts - but nothing 'well known' like Rudin, Spivak, or something like that. – Joe Dec 08 '12 at 00:00
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    @JakePetroules There actually is a Unicode symbol, called Questioned Equal To: ≟ – mic Oct 25 '18 at 23:33
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    ≟ is the unicode symbol. Unicode: U+225F, UTF-8: E2 89 9F – theRealKlanni Nov 07 '18 at 18:23
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≟

The Unicode symbol ≟ can be used for questionable equality.

Unicode Reference: https://www.compart.com/en/unicode/U+225F

hayesgm
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