I created a question with \varnothing to denote empty set.

In the preview it played nice, but on the question page \varnothing was replaced with \emptyset for some mysterious reason.

Why \varnothing does not work?

  • $\begingroup$ FWIW, it works at the sand box here. $\endgroup$
    – user21436
    Commented Aug 24, 2012 at 17:03
  • $\begingroup$ It is displayed ok for me in your question How is it called a minimal morphism of category Rel? $\endgroup$ Commented Aug 24, 2012 at 18:31
  • $\begingroup$ @MartinSleziak: In this my question it looks for me as \emtpyset not \varnothing. It's weird that we see different things. $\endgroup$
    – porton
    Commented Aug 24, 2012 at 21:26
  • $\begingroup$ If there is a problem with the way something is displayed, then you should probably add a screenshot and mention which OS and browser you are using. $\endgroup$ Commented Aug 25, 2012 at 5:36
  • $\begingroup$ @MartinSleziak: Firefox 14.0.1 Debian Linux. screenshot: i.imgur.com/lt0uo.png $\endgroup$
    – porton
    Commented Aug 25, 2012 at 10:45

2 Answers 2



varnothing $\varnothing$

emptyset $\emptyset$

Well, it seems to work for me. That's too bad.

  • 4
    $\begingroup$ I can confirm the "wrong" symbols (both Safari 5.1.7 and FF 14.1 on Mac OS X 10.6.8): screenshot, while the preview looks fine. Concerning differences between preview and actual post see Willie's comment here. See also my comment here for ... $\endgroup$
    – t.b.
    Commented Aug 25, 2012 at 6:53
  • 3
    $\begingroup$ ... a manifestation of somewhat erratic behavior of $\varnothing$ and $\emptyset$ in comments. I noticed similar glitches with \setminus and \smallsetminus but can't remember an instance off the top of my head. $\endgroup$
    – t.b.
    Commented Aug 25, 2012 at 6:54
  • $\begingroup$ I'm also getting the symbols switched, both here and in the question and answer referenced by the OP (but not in the preview). $\endgroup$ Commented Aug 25, 2012 at 16:09
  • $\begingroup$ @t.b. \setminus shows up as a long backslash in preview but as a small backslash in the final post. $\endgroup$
    – Zhen Lin
    Commented Aug 26, 2012 at 15:37
  • $\begingroup$ It looks like the difference people are seeing depends on whether they are using the STIX fonts or not. With STIX fonts, the two macros are reversed. I will look into it further. $\endgroup$ Commented Aug 27, 2012 at 23:19
  • $\begingroup$ OK, here's what I have found: STIXGeneral has the glyph for \varnothing in the unicode position for U+2205 (EMPTY SET), while the glyph for \emptyset is in that position in STIXVariant. MathJax sets things up to get the right one when STIX is used, but unfortunately there is a timing problem and the TeX input has run before the change is made, so the output is reversed. But for previews, the TeXing occurs later, after the change is made, so it looks right. I think \setminus is a similar problem. I will look into fixing it for the next release of MathJax. $\endgroup$ Commented Aug 27, 2012 at 23:44
  • $\begingroup$ @Davide Makoto has reported that our sandbox has become slower. Can you see anything there that might be slowing down MathJax? I presumed with the older answers deleted all would be well. Thoughts? $\endgroup$ Commented Aug 28, 2012 at 22:43

MathJax v2.1 should resolve this issue. Math.SE is now using the beta version of MathJax v2.1, so you should see the correct rendering for these characters now (both the empty sets and the setminus issues should be fixed). Please let me know if that is not the case.

Note that if you keep your browser open continually, you may need to empty the cache and reload the page (or perhaps even restart the browser) to get the new copy of MathJax. (MathJax's About box should tell you which version you are getting; make sure all the files in the list show v2.1).

See MathJax 2.1 beta for more details on the changes in MathJax v2.1.

  • $\begingroup$ As always, many thanks for MathJax support. $\endgroup$ Commented Oct 4, 2012 at 15:05

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