Would disallowing displayed equations ("double dollars") in titles be useful?

Question

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.)

Answer 1

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.

• What are the sense and reference of the propositions $R \notin R$, $R \in R$, where $R=\{x \mid x \notin x\}$ in Frege's Grundgesetze?

  The original title source was What are the sense and reference of the proposition $R$$\in$$R$, where $R$={x|x$\notin$x} in Frege's Grundgesetze? which used $$ to achieve immediately adjacent inline math expressions. The title was later edited to change $R$$\in$$R$ to $R$$\notin$$R$. Even later edited to remove immediately adjacent math expression.

• What is the independence number of this graph which is a generalization of a Kneser graph?

  The original title source was (inexplicably) Calculation Clique number of a special graph which is a generalization of Kneser graph$$, which used $$ for no real purpose that I can think of. This was later edited out.

• An apparent equivalence of the category of affine schemes over $S$ and the category of quasi-coherent $\mathcal{O}_S$-algebras

  Original title source was $\{$Affine schemes over $S$$\}$ $\cong$ $\{$$\mathcal{O}_S$ - algebras$\}$? which again uses $$ for immediately adjacent math expressions. Later edited to remove immediately adjacent math expression.

• A variant of Freiling's Axiom of Symmetry and a weak form of the Continuum Hypothesis in models where all sets of reals are Lebesgue measurable

  Original title source was Does $ZF$+$LM$+$A_{\lt2^{\aleph_0}}$ imply $\lnot$$WCH$?. Again, immediately adjacent math expressions, since edited.

• Sets of Vitali's type in models of $\mathsf{ZF}+\mathsf{GCH}$ where $V \neq L$

  Original title source was A question regarding sets of Vitali's type in models of $ZF+GCH$ where $L$$\neq$$V$. Immediately adjacent math expressions, since edited.

• Is the reduced plethysm (restricted to 2-columns in Young tableaux) of this Schur funtion known $\mathbb S_{3^1}(\mathbb S_{1^p})$?

  Original title source was Is the reduced plethysm (restricted to 2-columns in Young tableaux) of this Schur funtion known $$\mathbb S_{3^1}(\mathbb S_{1^p})$$? which did use $$ for displaymath. Later inlined.

• Any grammar for the language $L =a^p$, $p$ is prime number of $\mathbb{N}$

  Original title source was Any grammar for the language $$L =a^p$$,p is prime number of $$\mathbb{N}$$ which did use $$ for displaymath. Later inlined, and otherwise fixed.

• Showing $\int f_{n+1} dx / \int f_n dx\to 0$

  Original title source was showing $\int f_{n+1} dx / \int f_n dx\to 0$, later edited to showing $$\int f_{n+1} dx / \int f_n dx\to 0$$ to introduce displaymath, and was later inlined.

• Rewriting a series $\sum_{n=0}^\infty \frac{1}{n!}(\Delta^\varepsilon)^n a_n$ in the form $\sum_{n=0}^\infty c_n \varepsilon^n$

  Original title source was combinatorics problem, edited to combinatorics problem: $$ \sum_n a_n (\sum_k b_k \epsilon^k )^n $$ to include displaymath (and be a bit more descriptive of the content). Since edited to remove displaymath.

• Is there a brief name for the symmetric space $SL_{2n} / Sp_{2n}$?

  Original title source was Is there a brief name for the symmetric space $SL_{2n} / Sp_{2n}$$? which had $$ as a mistake, later corrected.

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.