This elaborates on a comment I made on David Speyer's meta post.

Someone posted at least one problem from this year's PROMYS application on MO--without labeling it as such, of course. One concerned trains traveling at different speeds on a single track. After Speyer's post, the problem was removed, understandably. I was one of at least two people who posted answers to that question; those actions and the resulting reputation points seem to have disappeared from the system.

Now that the application deadline has passed (15 March), can we consider reinstating the question and answers? While the person posing the question violated MO rules, the question is engaging, we who posted answers were acting in good faith, and the answers attracted some interest.

  • 3
    $\begingroup$ For comparison, on Mathematics there is a clearly formulated procedure how the moderators deal with questions from ongoing contests: “Contest problem” policy. $\endgroup$ Commented Mar 17, 2021 at 8:29
  • $\begingroup$ we could just vote to undelete, if we know the link to the deleted question... $\endgroup$ Commented Mar 17, 2021 at 12:14
  • 8
    $\begingroup$ As mentioned in some of those other threads, there is the problem that PROMYS reuses questions year after year. But they can't expect MO to ban a certain question forever... $\endgroup$ Commented Mar 17, 2021 at 13:17
  • $\begingroup$ @CarloBeenakker That depends. If the question was deleted by a moderator, it cannot be undeleted by regular users. (All details are explained in the FAQ post on deletion. There is also a related feature request: Regular users should be able to vote to undelete moderator-deleted posts.) $\endgroup$ Commented Mar 17, 2021 at 16:34
  • 3
    $\begingroup$ it was user deleted; the policy linked to above says "If the "contest" has no definite duration, then we do not consider questions on it as contest questions for this discussion. This is to prevent indefinite lock-down of information." --- so I would presume undeleting is allowed; I do have the link, shall I post it here? $\endgroup$ Commented Mar 17, 2021 at 16:42
  • $\begingroup$ @CarloBeenakker The "policy" I linked is the policy formulated on Mathematics - which is a different site from MathOverflow. If MO decides (at some point) to create a policy about this issue, it might be different. In case it wasn't clear, I will stress that my comment which links to the FAQ post was concerning the question whether undeletion is technically possible. $\endgroup$ Commented Mar 17, 2021 at 16:58
  • $\begingroup$ I appreciate the comments. @CarloBeenakker, thanks for finding the link. Without waiting for something official about contest questions, would it be appropriate for you to post it here in an answer and see if there's sufficient interest to undelete? (Or do reopening votes occur behind closed doors somewhere?) $\endgroup$ Commented Mar 18, 2021 at 21:02
  • 1
    $\begingroup$ mathoverflow.net/questions/385370/… --- only visible by 10k+ users --- I presume if we undelete and it is considered inappropriate we can always delete it again. $\endgroup$ Commented Mar 18, 2021 at 21:15
  • 3
    $\begingroup$ @BrianHopkins: But if we accept such questions for high-school pupils on MO, what will MSE be left for? A contest problem may very well be interesting and difficult, but this shouldn't be enough to consider it "research". $\endgroup$
    – Alex M.
    Commented Mar 19, 2021 at 23:15
  • 1
    $\begingroup$ @AlexM. Remember that it was answered when it was not yet identified as a contest question. And it's still closed. I'm glad, though, that it is accessible again, with the same status as other closed questions, rather than being hidden. As to whether it is "research," there are many publications that establish combinatorial proofs for recurrence relations, for instance. $\endgroup$ Commented Mar 20, 2021 at 19:20

1 Answer 1


This is a genuinely tricky question. I incline toward agreeing with the policy that while we can try to keep problems off the site while applications are open, we can't be expected to play whack-a-mole forever. This question from 3 years ago: Set of rational numbers generated by some rules was flagged as a PROMYS problem. My personal feeling was that this question is past the statute of limitations. I'm less sure about undeleting the question under discussion; I guess I will let non-moderators users decide whether to undelete it unless we come to a clearer consensus.

I think PROMYS may need to just accept that these problems are going to get on the internet and there is only so much that we can do. Certainly reusing problems many years in a row is just asking for trouble.

That said, I think users should exercise some judgement on this point. MO doesn't have a contest policy, but it does have a homework policy (that is, no homework help). I would say these questions are effectively homework, and I think it should have been clear to the people answering them that they were homework; probably both these problems should have been migrated to math.SE anyways.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .