Prompted by Gro-Tsen's recent meta question, it appears that now may be a good time to rethink our site-specific close reasons here on MathOverflow.


If you have sufficient rep, you can click the "close" button on a question (or the equivalent "flag" → "needs improvement", which is available for almost all users), and you get a popup which looks like this:

General Close Reasons

These are some general close reasons common to the entire Stack Exchange network as I understand, and which, if we wanted to change them, would at the very least require some discussion with Stack Exchange (and they might tell us no).

What we do have control over is the options you get if you choose the second option on this list -- the community-specific reasons. If you do that, you get the following options:

Site-Specific Close Reasons

We currently have two options here, and we can have up to three. As a technical point, it appears to be possible for moderators to delete a close reason or to create a new one, but not to edit the description in an existing close reason. We can also tinker with the order they appear in.


It's hard to trace these sorts of things all the way back to the beginning of MO, but in addition to the current two site-specific close reasons, the software currently remembers two deactivated ones, which read:

MathOverflow is for mathematicians to ask questions to each other about their research. Questions about homework are generally off-topic.

Questions about homework are generally off-topic. MathOverflow is for mathematicians to ask each other questions about their research.

I suspect that one of these reasons at some point replaced the other, as a minor rewording. Judging by this old meta discussion, it appears that this close reason (containing the word "homework") was retired in 2013 in favor of the current close reason which mentions Math Stack Exchange. At the time, no specific rationale was recorded for dropping the word "homework", but I think I agree that explicitly labeling a question as "looking like homework" is not something we want to be doing in our question-closing process.

Why do we close questions, anyway?

We have recently revamped the help page which describes what's on-topic and what's off-topic on MathOverflow, as suggested by Matt F. in this meta discussion. Currently, that help page lists the following possible reasons that a question may be off-topic:

  1. The question looks like homework.

  2. The question is a discussion question.

  3. The question asks for a broad exposition or encyclopedia article on a topic.

  4. The question asks for OP's or somebody else's work to be checked.

  5. The question is really just an announcement of results.

  6. The question asks a well-known open problem.

  7. The question has been inappropriately cross-posted on another site.

  8. The question is a meta MathOverflow question.

In addition, the user is advised to avoid the following types of questions until they gain a bit of familiarity with the site:

  1. Questions asking for a list of something.

  2. Questions about the workings of the mathematical community rather than about mathematics per se.

Question 1: Are we missing any important close reasons here?

Analysis of Close Reasons Needed:

It appears to me that, with a few exceptions, most of the above close reasons are well-covered by the close reasons one is allowed to select when voting to close a question:

  1. Homework -- not about research math.

  2. Discussion -- needs focus / opinion based.

  3. Encyclopedia -- needs focus.

  4. Checking work -- ?? As suggested by Gro-Tsen, we could perhaps use a specific close reason for this.

  5. Result announcement -- ?? If the question is not really a question, in principle we shouldn't need a site-specific close reason. Probably "opinion-based" should cover cases like this. But perhaps there's something to be said for having a close reason which allows this to be lumped with "work-checking".

  6. Open problem -- ?? I think that "needs focus" should cover a case like this -- the point is that if you're asking about an open problem, you should be asking some more specific question than just "what is the solution?". However, because "needs focus" is not a site-specific close reason, we can't edit it to point out that specifically, questions about open problems need a very particular kind of focus. So perhaps it would make sense to have an additional close reason covering this case.

  7. Cross-post -- duplicate ?? I realize now I'm not sure how we usually handle inappropriate cross-posts.

  8. Meta -- not about research math.

  9. (Lists) -- needs focus.

  10. (Mathematical community) -- not about research math.

So by my count, there are up to 3 4 close reasons which could be formalized in addition to the ones we have, but only 1 slot to put them in. So some sort of prioritizing or lumping-together needs to be done.

Question 2: Which of the 3 4 close reasons with question marks above is the most important to give a close reason to? More broadly, what would be the ideal way to use our 3 allotted slots of site-specific close reasons?

For example, one possibility would be to keep the two existing close reasons we have, and to additionally add something along the lines suggested by Gro-Tsen. In that case, we'd just need to nail down the details a bit more.

(Note that there's also the option to provide a custom close reason which you write on the spot. If a close reason is rare enough, it can be covered by that.)

Analysis of the close reasons we have:

Note also that the two site-specific close reasons we currently have are similar -- one is "not about research math", while the other is "not about research math, and here's a link to Math.SE". It seems to me these should be modified to give a little more clarity about when one should be chosen over the other. This leads into the final point.

Technical Point:

Since 2019 we have the flexibility to have the close reasons we use display differently to different users. For instance, the message shown to a prospective close voter can be different from the message shown to a prospective close votee.

I bring this up because it may be relevant to us when it comes to the two existing close reasons -- we could consider adding some guidance for close-voters over when to choose the one which links to Math Stack Exchange and when not to (I think the main point is: don't choose the Math Stack Exchange one unless you're sure the question meets the standards of Math Stack Exchange questions.)

Question 3:

What specifically should our site-specific close reasons say?

This question is mean to include the specifics of any potential new close reasons, as well as any potential changes to the wording of existing close reasons (technically to change the wording, the process is to delete the old close reason and replace it with a new one, but I think we should be open to doing something like that at this time with our existing close reasons.)

  • $\begingroup$ In our custom reasons pane, can we have three plus the "other" option? I think it's handy having that as a backup in case. But I'm willing to be convinced that we might not need it, if the given reasons are better suited for what we need $\endgroup$ May 9 at 23:58
  • 3
    $\begingroup$ @DavidRoberts Ah yes, the count of 3 does not include the "other" option. $\endgroup$
    – Tim Campion Mod
    May 10 at 0:14
  • 1
    $\begingroup$ As to "7. Cross-post -- duplicate." -- Unfortunately, cross-posted questions cannot be closed as duplicates, as the duplicate must be on the same site. $\endgroup$
    – Stefan Kohl Mod
    May 10 at 8:02
  • 2
    $\begingroup$ The "open problem" option is a quite bad one to my opinion. Many good questions turn out to be good open problems, which nobody wants to close. One certainly has in mind those "famous" open problems, which attract lots of poor questions. And maybe less famous but well-documented ones. (I remember some abusive closure votes, when one OP, for a very specific, presumably original problem, instead of asking "is this true", said "I conjecture this is true".) $\endgroup$
    – YCor
    May 10 at 8:24
  • $\begingroup$ Not a useful contribution I'm afraid, but I have to say, StackExchange limiting the number of site-specific close reasons to such a small number as 3 seems strangely petty: it's not like a reason to close is resource-consuming, and since they're chosen by the site moderators, it's not like J. Random User can add their own. (I'm not saying having two dozens would be wise, but putting a hard limit at just three… come on!) $\endgroup$
    – Gro-Tsen
    May 10 at 22:43
  • $\begingroup$ @Gro-Tsen Judging by the response this discussion, it seems that SE can add more custom close reasons when requested: Can we have more than 3 custom close reasons, pretty please? (Specifically, this is about adding one more custom close reason on Ask Ubuntu. The same post says that Stack Overflow has 5.) The linked post is from 2013 - I do not know whether things changed since then. I would expect something like this to be rather rare. $\endgroup$ May 11 at 4:36
  • $\begingroup$ I would be in favour of any "checking work" closure reason, to allow the querying of some specific technical aspect of a piece of work (provided the question met all the other acceptance criteria) but dissallowed extensive checking of multiple components of a lengthy exposition. $\endgroup$ May 11 at 8:49
  • 1
    $\begingroup$ Also, given the broad range of closure reasons and the small amount of sapce available for pre-canned explanations, is it possible to include text within the dialog box that the CLOSER sees encouraging them to leave a comment explaining their vote (or even better a space for them to enter their comment). Otherwise, when the OP is directed to a policy page with such a broad range of reasons, it will often be unclear to them which reasons are specific to their case. $\endgroup$ May 11 at 8:55

1 Answer 1


My suggestion would be to merge the two existing site-specific close reasons (which are too confusingly similar anyway) into a single one, like:

  • This question does not appear to be about research-level mathematics: see the help center for explanations. General questions about mathematics may be appropriate on Math.Stackexchange.

(Maybe adding “homework excepted” so we don't blindly redirect homework to MSE? Or is this too long?)

Then have a second one like:

  • MathOverflow is not a forum to post announcements of new results or proofs to be checked.

This would still leave a possible third reason, to be filled in now or later.

  • 6
    $\begingroup$ I think that there is a meaningful difference between "this post does not belong on MO or MSE" and "this post is not the right level for MO, but could do well on MSE." (MSE folks have explicitly asked, reasonably, that we not view MSE as a dumping ground for all questions that don't belong here.) I don't think that the current wording makes this as clear as it could be, but I'm not sure that doing away with the distinction entirely is the solution. $\endgroup$
    – LSpice
    May 10 at 23:23
  • 1
    $\begingroup$ It seems that the two close reasons were introduced here: Revamping the closure reasons. (This thread is already linked in Tim Campion's post.) Several posts linked to that post are related to the fact that they are similar and whether or not it is good to have them as two separate close votes reasons. $\endgroup$ May 11 at 4:31
  • 1
    $\begingroup$ I have rarely seen an off topic question here that would go down well on MSE. Yes, there are examples, but they are few. Most of the stuff we close for "level" wouldn't fit into MSE. So, let's not suggest people to go there if their questions are not up to pat and will be closed anyway. It's cruel to them and it's cruel to the MSE community. $\endgroup$
    – Asaf Karagila Mod
    May 14 at 6:39
  • $\begingroup$ @AsafKaragila Well, at the moment all available custom close reasons are formulated in a way which directly or indirectly leads to Mathematics. (There is an option to migrate and the close reason which has a direct link to that site. And the third one links to the help center - if the user actually bothers reading it, they'll get to the list of sites which includes Mathematics. At the same time, if somebody is willing to read the help center, perhaps they would at least have a look at the guidelines for new MSE users.) $\endgroup$ May 14 at 9:22
  • $\begingroup$ In the other words, I would consider sending a user to Mathematics perfectly find - provided they are given some pointers to things which are expected from posts on that site. For example, I have seen comments on MO which are somewhat similar to the suggestions given here: Comment template for questions more appropriate for MSE. $\endgroup$ May 14 at 9:26
  • $\begingroup$ I like the proposed "not a forum to post announcements of new results or proofs to be checked" but as currently worded, it sounds like it's limited to questions of the form, "Is my proof of P=NP correct?" and does not include "Has anybody checked John Doe's recent arXiv preprint claiming to prove P=NP?" Perhaps it could be reworded to include both types of questions, since the latter are also common, and usually merit closure. $\endgroup$ 11 hours ago
  • $\begingroup$ @TimothyChow I see what you mean; on the other hand, saying, e.g., “not a forum to post announcements of new results or checking the correctness of proofs” would be too broad (we can and do discuss the correctness of proofs on MO). Maybe “not a forum to post announcements of new results or checking the correctness of their proofs”? $\endgroup$
    – Gro-Tsen
    5 hours ago

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