Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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.

share|cite|improve this question
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 7 '12 at 23:50
That's what I've usually seen as well - what Tom suggested. – Joe Dec 7 '12 at 23:51
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 7 '12 at 23:53
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 7 '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 8 '12 at 0:16
up vote 4 down vote accepted

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.

share|cite|improve this answer
No Unicode symbol for a question mark over an equals sign? – Jake Petroules Dec 7 '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 7 '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 8 '12 at 0:00

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.