# Would disallowing displayed equations (“double dollars”) in titles be useful?

If a poster includes in the title some formula in enclosed between $$, like $$x^2+y^2=z^2$$$$x^2+y^2=z^2$$the title of the question will take up more space in various lists of questions, like here or here. I guess that we can agree that this is not a good way to use MathJax (LaTeX) in titles. A user posting such question could have done it by mistake. Or even on purpose, not knowing that this is not a good way to write title. At Mathematics Stack Exchange the the string $$ is included among things which are disallowed/blacklisted in the title, see: Using block (displayed) equations in question titles

Would blacklisting this on MathOverflow be useful, too? (As far as I know, moderators can request from the SE team changes in blacklisted tags, blacklisted words, etc.)

This is probably not a huge problem. I noticed it on one post made today. (But the title was edited during grace period. So I could not show this particular instance, not even by linking to the revision history.) I do not vouch for my SQL skills, but using this query this query I only found one question with such title: Rewriting a series $\sum_{n=0}^\infty \frac{1}{n!}(\Delta^\varepsilon)^n a_n$ in the form $\sum_{n=0}^\infty c_n \varepsilon^n$ (Which, I assume, will be edited soon after being mentioned on meta, so I will also add link to the revision history.) Other questions found by the query used constructs such as $a$$+$$b$ for $a$$+$$b$. (See the detailed answer by arjafi, which even includes the posts which has such title anywhere in the revision history.)

• Probably one would then need to disallow $\displaystyle{...}$ in titles as well(?) – Stefan Kohl May 22 '16 at 19:32
• Why? \displaystyle does not make the formula displayed on a separate line, which is the main problem here. – Emil Jeřábek May 22 '16 at 21:11
• Your SEDE query doesn't catch all questions with titles containing $$, but rather all questions whose titles end in $$. You should change the Title LIKE '%$$' to Title LIKE '%$$%'. You only catch a few more questions this way, and all the others use constructs like \$a$$b to have two immediately adjacent inline math equations (ugh). (Again, paltry reputation makes it impossible for me to edit this question. Really need to work on that.) – user642796 May 23 '16 at 3:41 • @arjafi Thanks of notifying me of the mistake. (I have updated the query and the post. Still it does not catch already edited instances, so thanks for your query and for the detailed answer.) – Martin Sleziak May 23 '16 at 4:54 • Speaking of titles, there are a few of them containing displaystyle. – Martin Sleziak May 26 '16 at 13:58 ## 1 Answer I understand the sentiment to have this blacklist, but I don't think it's really important for MathOverflow to have it. Very few questions have ever had $$ in their titles, and not always for actual displaymath.

Here is an SEDE query to catch all extant questions which have a revision where the title contained $$. Only 10 results pop up, so I'll look at each of them. This should be reverse-chronologically by question-creation date. So of these 10 questions, four actually used displaymath, while an equal number would are "false positives" in terms of having contained immediately adjacent inline expressions. The other two were "oddballs". For a point of comparison, running the same SEDE query on math.se yields 1203 results. And for some insider baseball, since its creation the $$ title blacklist has been matched on average about 1.5 times per day.

The small number of occurrences and the percentage of false positives seem to suggest that this is something that can be handled by the community on a case-by-case basis.

• While I agree with the conclusion, the "false positives" with adjacent inline expressions are terrible TeX abuse and need to be fixed no less than actual display math. – Emil Jeřábek May 23 '16 at 7:55
• @EmilJeřábek Unless you mean that TeX becomes a victim of some form of assault, I'd hardly call them "TeX abuse". Clumsy and inapt usage, sure, and certainly in need of fixing. – user642796 May 23 '16 at 9:09
• Victim of some form of assault: Hmm, intent is presumably missing here, but otherwise it sounds about right. – Emil Jeřábek May 23 '16 at 10:25
• Thanks for your effort to fix the problems! – Emil Jeřábek May 24 '16 at 9:24