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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.

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  • $\begingroup$ What context would you want to do this in? I would personally use an equals sign with a question mark above it. $\endgroup$ Commented Dec 7, 2012 at 23:50
  • $\begingroup$ That's what I've usually seen as well - what Tom suggested. $\endgroup$
    – Joe
    Commented Dec 7, 2012 at 23:51
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    $\begingroup$ What would you like a symbol that carries no information? Or if it should, what kind of information you would like it to have? $\endgroup$
    – dtldarek
    Commented Dec 7, 2012 at 23:53
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    $\begingroup$ From a logical point of view, $(a=b)\lor (a\ne b)$ is a tautology. One can condense it by saying nothing. $\endgroup$ Commented Dec 7, 2012 at 23:56
  • $\begingroup$ 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? $\endgroup$ Commented Dec 8, 2012 at 0:16

2 Answers 2

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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.

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  • $\begingroup$ No Unicode symbol for a question mark over an equals sign? $\endgroup$ Commented Dec 7, 2012 at 23:53
  • $\begingroup$ 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. $\endgroup$
    – Joe
    Commented Dec 7, 2012 at 23:55
  • $\begingroup$ 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. $\endgroup$
    – Joe
    Commented Dec 8, 2012 at 0:00
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    $\begingroup$ @JakePetroules There actually is a Unicode symbol, called Questioned Equal To: ≟ $\endgroup$
    – mic
    Commented Oct 25, 2018 at 23:33
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    $\begingroup$ ≟ is the unicode symbol. Unicode: U+225F, UTF-8: E2 89 9F $\endgroup$ Commented Nov 7, 2018 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

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