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The purpose of this thread is to focus the attention of the community on posts that may require reopen and undeletion votes. A request should be posted as an answer below (one request per answer).

Some guidelines:

  • Please be polite, and respect the many different viewpoints in our diverse community. This goes for the person making the request as well as those commenting on it.

  • There is a reopen queue. Please wait until a post has gone through this queue, before posting here. Notice that the first edit after the question is closed pushes the question into the reopen review queue if the edit is done within 5 days of closure, and so does a reopen vote. (If the review has already been finished, it is shown on the timeline of the question.) When in doubt, wait 24 hours after the last substantive action.

  • To inform readers of the current (and past) states of the targeted post, please add the information Reopened or Undeleted at the start once the request has resulted in some action. (If the action is undone, add this too, like Reopened, Reclosed.)

  • Do not only post a request, like "request reopening of link". Instead, make a case for your concern. Yet keep in mind that it can be easier to get your request handled if you try to frame it in a way that takes the feedback the post received into account positively rather then seeking confrontation. Also, try to improve the post before posting here.

  • In case of "small" requests, like one missing vote, it can make sense to ask in chat instead of posting here. The room CURED is a reasonable place for such requests. The same guidelines apply there.

  • If you are involved in the thread which you post about (e.g., you asked the question or you answered it), please disclose this.


Earlier versions of the thread that served as a model:

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    $\begingroup$ If I understand correctly, it is not ok to post undeletion requests if one of the deletion votes was from a mod right? I assume that it is not, but I just want to be sure. Also, feel free to delete this comment if it is appropriate, or ask me to delete it and I will. $\endgroup$
    – user33907
    Apr 7 '21 at 3:45
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    $\begingroup$ @HereToRelax To weigh in on that, I don't see why it wouldn't be OK, but only a moderator could help you. One would guess that it would be more appropriate to flag, but that doesn't really allow for back and forth discussion. $\endgroup$ Apr 7 '21 at 20:25
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    $\begingroup$ You are always welcome to discuss questions which a moderator has voted to delete. If you are asking about this question, it is worth noting that my delete vote was cast in 2019, before I was a moderator. I stand by that vote---even with the minor clarification in the comments, the question still lacks context---but you are welcome to discuss the question. If you can find two people who agree with you, the question can be undeleted. $\endgroup$
    – Xander Henderson Mod
    Apr 8 '21 at 14:47
  • $\begingroup$ @XanderHenderson: There may never be a perfect time to close this (last year's thread) and start a new one, but things are about as quiet as they could be. $\endgroup$
    – hardmath
    Jan 5 at 19:54
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    $\begingroup$ @hardmath I am out of town right now, and not very engaged with Math SE. However, I agree that a new thread should be made. My understanding is that creation of the new "Reopen & Undelete" thread is a kind of hazing ritual for new moderators, so maybe one of the new mods should do it. :D $\endgroup$
    – Xander Henderson Mod
    Jan 6 at 3:15
  • $\begingroup$ @hardmath There is no reason to keep creating new threads. In fact it is better not to, since then there are always (many) prior requests visible (and easily accessible) - which sheds light on the current community consensus on such exceptional matters (which e.g. may discourage noise: requests doomed to fail). See also old discussion on such $\endgroup$ Jan 6 at 10:29

60 Answers 60

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Reopened, Re-closed (by a mod), and Reopened again with context edit reinstated

Please consider reopening Any criteria for a category to have all connected limits?. This is a very natural question about whether there is an analogue of certain well-known basic theorems in category theory in a less well-known context. The context in the original question was quite clear to anyone familiar with the area but was only in a brief parenthetical at the end of the question. I have expanded on this and improved the presentation a bit to make it more accessible to non-experts.

It seems to me that this is exactly the sort of question that this site was built for: questions that may naturally occur to many people (not just some exercise that is of no particular interest), do not have obvious or "standard" answers that can be found in every textbook on the subject, and by having an answer here the answer will be easily findable with a search engine.

[Disclosure: I have answered the question.]

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    $\begingroup$ The question was appropriately closed for lacking context. You then edited the question to insert material which is not clearly the product of the original asker's intentions. This version of the question was reopened. As the edits were inappropriate, they were rolled back. I have reclosed the question. $\endgroup$
    – Xander Henderson Mod
    Jul 8 '21 at 12:52
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    $\begingroup$ For future reference, please read the guidelines on rewrites and context edits. $\endgroup$
    – Xander Henderson Mod
    Jul 8 '21 at 12:53
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    $\begingroup$ Reading the guidelines, it says that one can clarify the phrasing and add relavant basic definitions, which looks to me like what you have done. In particular no ‘attempt’ was added. So, is it that too much context was added so that the question was changed fundamentally? $\endgroup$ Jul 8 '21 at 16:41
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    $\begingroup$ @CalvinKhor: Indeed, I was trying to follow the guidelines and it is not clear at all to me how I violated them. I have messaged the mods to ask for clarification. (And if this edit violates the intended meaning of the guidelines, I think the guidelines themselves need some significant edits to make that clearer.) $\endgroup$ Jul 8 '21 at 16:42
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    $\begingroup$ +1, voted to reopen - this should be reopened and Eric Wofsey's edit should be restored. It seems like exactly the sort of context-adding edit that would be appropriate under the guidelines: it added a relevant definition, some simple background and motivation, and one small related theorem of similar level to those already mentioned by the OP, exactly as suggested. If this isn't acceptable, what is? $\endgroup$
    – KReiser
    Jul 8 '21 at 18:36
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    $\begingroup$ Overly zealous application of guidelines leads to removal of significant mathematical content from m.se. Again. Sad. $\endgroup$ Jul 8 '21 at 23:44
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    $\begingroup$ Searching in CURED for this question gives a few hits: chat.stackexchange.com/search?q=4164403&room=2165 (Also, to be fair, the content has not (yet) been removed) $\endgroup$ Jul 9 '21 at 1:09
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    $\begingroup$ Crucially the decision to rollback the edits made by Eric to improve the Question was not made by a moderator but by a user who espouses the view that no one should be allowed to improve the body of the Question except the OP. I know this from personal experience of adding material from Comments left by the OP into the body of the Question, and being "told off" for doing so. But it is not in the spirit of this Community to judge improvements so harshly. $\endgroup$
    – hardmath
    Jul 9 '21 at 2:38
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    $\begingroup$ The other problem is with an inactive OP and how we could work out editing posts of inactive/suspended/removed OPs. Perhaps reasking the question with context and self-answering is a possibility, as was recently done on meta. This would be my suggestion in that case : then find the OP of the original question and redirect them to your question. $\endgroup$ Jul 9 '21 at 6:55
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    $\begingroup$ The situation with this question is shocking to me. Eric's edits were fairly minor and a clear improvement. They did not change the intent or core content of the question at all - but they did greatly improve the presentation. To me, they seem squarely in line with the guidelines. The OP has even signaled approval in the comments. I do not understand the motivation to roll back the question to its earlier, lower quality form... $\endgroup$ Jul 9 '21 at 20:49
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    $\begingroup$ @AlexKruckman It's not shocking to me—it's yet another example of the moderators/power users of MathSE enforcing the rules inconsistently to how they are written. The fact that mathematicians do this, given that one could argue the entire point of the last two centuries of mathematics has been to systematically root out inconsistency, is however bewildering. $\endgroup$ Jul 9 '21 at 22:49
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Reopened, reclosed, reopened again, closed once again, and reopened once again

Please consider reopening this Question, which was closed for lack of context.

Yet the original opening paragraph gives the following context:

I have a young group of kids (30) playing soccer and they need to be put into 6 teams of 5 players for each round of matches. All 6 teams play at the same time on adjoining fields.

I make a point of bringing this to the Community's attention because there has been something of a historical pattern with these kinds of problems. The asker has (or claims to have) a real world motivation for asking about a certain kind of block design. The Question has a definite mathematical formulation and solution, often one that is not obvious without a certain amount of trial and error computation (though occasionally the literature provides an answer).

None of the five close voters left a Comment to record what in the way of additional context would improve the Question to their satisfaction.

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    $\begingroup$ Most combinatorial design questions require decades of research and computational time to answer, so it infuriates me when questions like these are closed with a comment like "well, what have you tried?". Presented with such a hard problem in real life, most mathematicians would be stumped, let alone laymen. $\endgroup$ May 6 '21 at 17:48
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    $\begingroup$ @MikeEarnest: Right, a typical user might well not know how to tackle problems that they have a real world motivation for. I want to see their context, but "what have you tried" is not the gold standard here (though this user did suggest they'd thought about complete block designs because they said it wasn't what they wanted). $\endgroup$
    – hardmath
    May 6 '21 at 18:40
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Undeleted (still closed), Deleted, Undeleted, Deleted again, Undeleted again, and yet deleted again, and locked – permanently! – by moderator Xander Henderson

The question What are sufficient conditions for a number to be irrational or transcendental? was closed as a duplicate of Proving irrationality and then deleted (along with answers with scores of $+12,+7,+4,+4$).

I suggest the newer question is not a duplicate of the older one. The newer question asks about proving irrationality, proving transcendence, and asks for books on these topics. The older question asks only about proving irrationality.

Please consider voting to undelete the question.

In the interests of full disclosure, I posted an answer to the question (scored $+2$).

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    $\begingroup$ It would be nice to know why those voting against this request think that a question about transcendence and references is a duplicate of a question which is about neither of those things. $\endgroup$ Sep 13 '21 at 6:02
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    $\begingroup$ Upvoting this post, but not voting to reopen. Gerry, I'm uncomfortable with questions of this type. The scope is too wide in my opinion. Non-overlapping books have been written about proving irrationality and transcendence respectively. On the other hand, if we improve the question by giving it a more specialized focus, then each and every choice of focus is likely to lead to a question that has been handled already. True, we do allow reference requests, but I prefer those with a rather narrow focus. Otherwise they become lists of textbooks ranked by popularity rather than merit. $\endgroup$ Sep 14 '21 at 4:29
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    $\begingroup$ (cont'd) Anyway, the site may benefit from having a wider discussion about what we like to see in a reference request. It is not easy to give a definitive list of criteria. My judgement is that the linked is too unfocused, but there is a lot of scope for differences of opinion. $\endgroup$ Sep 14 '21 at 4:32
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    $\begingroup$ @Teresa, I think it's a little odd to judge a question by the answers it gets. Also, I think there's no such word as "duplicacy". There's "duplicity", but that means something entirely different. $\endgroup$ Sep 14 '21 at 8:05
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    $\begingroup$ @Teresa, it's impossible to know why other users downvoted my answer. And possibly the other answerers weren't as well-informed about references as I was, or just thought they could help more by sharing what they knew about the mathematics than by directing OP to the library. Who knows? Anyway, I haven't asked for the question to be reopened, I'm just glad it has been undeleted (and hope it stays that way). $\endgroup$ Sep 14 '21 at 9:53
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    $\begingroup$ "Please avoid extended discussions in comments. Would you like to automatically move this discussion to chat?" No, thanks. $\endgroup$ Sep 15 '21 at 12:32
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    $\begingroup$ @user21820, maybe so, but the one thing even you evidently agree to is that it's not a duplicate. Closing and deleting it as a duplicate was an error. Keep it closed, if you like, but don't delete it, as that deletes some useful answers as well, answers that don't duplicate what's at the earlier question. [the answers currently stand at 15, 10, 7, 7, and 4. $\endgroup$ Sep 17 '21 at 14:06
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    $\begingroup$ @user21820, I'm saying we shouldn't delete a question as a duplicate when it isn't a duplicate, and we shouldn't vandalize the site by deleting helpful mathematical content. $\endgroup$ Sep 17 '21 at 14:11
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    $\begingroup$ @user21820 I agree with you... Users should not vandalize the site by going against quality standards by deleting questions based on their own opinions not on quality standards... I mean many users want the question .... but other users exploit their high reputation and authority on the site.... and it is not forbidden and wrong to be motivated by open problem...high level users also should respect the effort done by answerers ....the answerers also are high level they are:1)Thomas Andrews 158k reputation , 2)Gerry Myerson 165k reputation, 3)Lubin 57k reputation 4)slugger 5k reputation. $\endgroup$ Sep 18 '21 at 11:09
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    $\begingroup$ @user21820, imagine that you haven't been exposed to a good treatment of questions of irrationality and transcendence. But you've seen some popularization that talks about $\sqrt2$ being irrational, and $\pi$ and $e$ being transcendental, maybe without even giving proper definitions of those terms, let alone proofs, and it mentions that it's an open question whether $\pi+e$ is rational. The topic interests you, and you want to learn more about it. You just might post a question like the one we're discussing here. You want to know how to do irrationality and transcendence proofs (continued) $\endgroup$ Sep 18 '21 at 11:22
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    $\begingroup$ (continued) and you want to know where to read up on these things, and that's about all you know how to ask. Now, I would want to encourage such a person to keep up an interest in math, and aim that person in a good direction. By closing and deleting the question, you're chasing OP away from mathematics (and in particular from this website). I think that's terrible. Please, have a little empathy for someone who is interested in math and just needs some direction. Vote to undelete. $\endgroup$ Sep 18 '21 at 11:25
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    $\begingroup$ The post probably should have been closed as too board. But it is really not too bad of a question. Voted to undelete. $\endgroup$ Sep 18 '21 at 11:36
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    $\begingroup$ @GerryMyerson I find it slightly ironic that you state both " I think it's a little odd to judge a question by the answers it gets", but that you take the time in your response here to list the scores of the answers which would be / have been deleted along with this question. $\endgroup$
    – Xander Henderson Mod
    Sep 19 '21 at 22:13
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    $\begingroup$ @Xander, Teresa was interpreting a question via the topics the answers chose to emphasize, I was evaluating a thread by the reception those answers got. The irony is slight, indeed. $\endgroup$ Sep 19 '21 at 23:42
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    $\begingroup$ I have locked the question in its current state in order to prevent a continuation of this [un]delete war. $\endgroup$
    – Xander Henderson Mod
    Sep 23 '21 at 17:59
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Undeleted

I'd like to tentatively nominate A structural view to the power set axiom: Is this axiom really justifiable? for undeletion (admission: I have an answer there). It was a fine question.

Re: the "tentatively" above, I'm not actually sure that undeletion is possible/ethical: at a glance it looks like what may have happened is that the OP deleted their account and requested that all of their posts be deleted as well. If that's the case - I'm not able to tell since I lack mod tools - then I don't think undeletion would be appropriate, but since I'm not sure it is (given that there it's not locked, so undeletion is possible) I'd like to bring it up.

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  • $\begingroup$ How did it get deleted in the first place? $\endgroup$
    – user33907
    May 24 '21 at 20:09
  • $\begingroup$ @Onir It says "deleted by community." I'm not exactly sure what that means. My best guess is what I state above, in which case unfortunately undeletion would probably be unethical, but on the off-chance that there could be a different reason I decided to bring it up anyways. $\endgroup$ May 24 '21 at 20:13
  • $\begingroup$ oh, but I don't think you can get all of your stuff deleted just because you want it. $\endgroup$
    – user33907
    May 24 '21 at 20:19
  • $\begingroup$ @Onir I recall some confusion on this point; I'm certainly not sure myself. $\endgroup$ May 24 '21 at 20:22
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    $\begingroup$ From what I can see from the post timeline, the user was destroyed and as a result all of their content was deleted (see deleted vs destroyed on the main Meta). The same post implies it is unlikely that a user can request their account be destroyed - it seems to be more applicable for spammers or other problem users. I don't think you need to be too worried about the ethics of undeleting here. $\endgroup$
    – KReiser
    May 24 '21 at 21:02
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    $\begingroup$ Remember that any post is legally the intellectual property of the SE corporate overlords, and not the property to the person who posted it. While users may delete content, there is no legal or ethical problem with the community undeleting it if it is considered useful. In this case, there is even less of an issue, as the user account no longer exists. $\endgroup$
    – Xander Henderson Mod
    May 24 '21 at 21:48
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Undeleted

https://math.stackexchange.com/a/3980921/43608

This is a deleted new answer to an old question (from february 2019), by a user that has been on MSE for 1 year and 10 months, but does not seem to have questions or answers yet.

The deleted answer is short, arguably too short, but would be at least a good hint in the correct direction (it was for me, when I tried to figure out whether to vote to delete or not in review queue).

The question is ambiguous, as noticed by the two answers already here, but I think the new one has the correct interpretation (that the coefficients $a,b,c$ are independent of $n$), since it leads easily to a unique solution, as expected.

I believe the deleted answer is correct while the two undeleted ones are not, and thus deserves to be undeleted.

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Undeleted

RKHS of functions vanishing at single point

Asker deleted the question soon after receiving an answer. The question is homework-like, but the asker showed a decent effort in my view.

I didn't vote to undelete since the answer is mine, and I wanted to see what others think.

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    $\begingroup$ What I think is, we don't like it when a user deletes a question for no apparent reason after there has been an answer. I voted to undelete. $\endgroup$ May 11 '21 at 8:55
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Reopened, Closed as dupe (as proposed)

This meta question on strange keyboard behavior was closed for clarification (and currently has a delete vote). It has since been updated to clarify that the problem was due to the (little known?) SE keyboard shortcuts - which can cause very puzzling problems if one is not aware of them.

As such, I propose to reopen then close it as a dupe of a prior related question on unexpected behavior caused by keyboard shortcuts. This will help improve matches to searches on such puzzling problems when they arise for other users. That no one on our meta recognized these shortcuts as the source of the problem seems to imply that giving this wider exposure here would be a good idea - not only to avoid wasting time debugging such strangeness, but also to give the shortcuts wider exposure to those who may find them useful.

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    $\begingroup$ I cast the last reopen vote and first close vote as dupe of proposed question, just now. $\endgroup$ Dec 9 '21 at 7:44
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    $\begingroup$ Closed as a duplicate now. (I could not help here because I cast a close vote on the original version of the question.) $\endgroup$
    – Martin R
    Dec 9 '21 at 9:17
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    $\begingroup$ Thanks to all. Hopefully this will help others to avoid pulling their hair out on encountering one of these strange interactions. $\endgroup$ Dec 9 '21 at 9:20
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Undeleted

Please undelete Functional Analysis: Finding finite functions over different norms as the question asker self-deleted his/her own question one day after receiving an answer.

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Reopened

Please consider reopening Looking for a Simple Proof of the Divergence of the Prime Harmonic Series. It is a natural question of wide interest and has a very clear implied context, of a teacher who wishes to present an elementary proof of a famous theorem to calculus-level students. It is not clear to me what additional context the close voters would have wanted or how the site would be better off without this question and others like it.

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    $\begingroup$ Not sure if there is a canonical post on this series yet. One candidate is here, another one with an interesting proof here. It seems that one should make a canonical one by merging several posts. $\endgroup$ May 24 '21 at 7:30
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Reopened

Please consider reopening Is there a metrizable topology on tempered distributions for which sequential convergence is pointwise?. This question was originally unclear but the asker has clarified what they meant. The question was also difficult to understand due to (I assume) a language barrier combined with some imprecise phrasing, and I've cleaned it up to be much clearer.

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DELETED

I want to know why the reason for closure of this question has been given as:

Questions about choosing a course, academic program, career path, etc. are off-topic. Such questions should be directed to those employed by the institution in question, or other qualified individuals who know your specific circumstances.

I do not see any reason for closure of this question.

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    $\begingroup$ The close reason is, I think, nonsense. However, the question does (in my opinion---note that I say this not as a moderator, but as a disinterested third party) deserve to be closed. It lacks context. $\endgroup$
    – Xander Henderson Mod
    Mar 2 '21 at 23:44
  • $\begingroup$ @XanderHenderson: Well, in that case am I permitted to delete the question because it is not useful for anyone anymore? And secondly, can you explain what more context could I have added in there? I didn't understand the statement of the question itself, so what ideas should I have been added there? Note that I know how to ask good questions on this site, as you can see my profile. $\endgroup$ Mar 2 '21 at 23:47
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    $\begingroup$ See How to ask a good question. In your case, I would suggest that the problem seems to depend on the definitions of "cofactor" and "minor". Quoting those definitions in your question would likely help to provide context (of course, a careful reading of those definitions might also clear up the confusion). $\endgroup$
    – Xander Henderson Mod
    Mar 2 '21 at 23:55
  • $\begingroup$ I should also point out, again, that when I say that the question should be closed for lack of context, I am merely expressing my opinion. I am not expressing the opinion of the moderating team, nor making a statement about site policy. I left the question in the state it was in an hour ago, but with a close reason that makes more sense. Other users may disagree, and may feel that the question ought to be reopened. That said, providing additional context will make it easier for others to vote to reopen. $\endgroup$
    – Xander Henderson Mod
    Mar 2 '21 at 23:57
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    $\begingroup$ The question has been deleted. $\endgroup$ Mar 24 '21 at 22:34
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Reopened

I asked a question about an identity involving large uniform random numbers here: Prove that $\lim_{m \to \infty} (\lceil m U \rceil -mU ) \sim U(0,1)$. The question is part of a larger theme of questions around proving a general result about point processes. I intend to write a paper on this topic and want to link these questions in the paper. It becomes harder to link questions that are closed like this and I also want to be able to add answers there in case I find a better, shorter way to prove the result in the future.

It was my mistake for not adding enough context, but I've done that now and linked to the other question. Can someone please re-open the question or let me know what other context I can provide to make it acceptable?

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undeleted, reopened

Please undelete the following question:

Union of closed convex sets

The question and (my - to be fair) answer was highly upvoted. The question was closed/deleted for lack of context. I edited the question to include some context: The claim seems to be true in situations one can immediately think of. It is one example of a claim on convex sets that seems to be true, but isn't.

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Undeleted.

Requesting to undelete "Trace identity for symmetric matrix".

The OP responded to some clarifying comments by me and Ben Grossmann, but after I posted my answer, they deleted their comments as well as the entire question.

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    $\begingroup$ In the future, you might consider raising a flag when something like this happens. I, personally, frown on the behaviour exhibited here (deleting a question immediately after getting answer). I believe that the other moderators feel similarly. $\endgroup$
    – Xander Henderson Mod
    Nov 10 '21 at 0:32
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    $\begingroup$ @XanderHenderson Thank you, I wasn't sure if it was appropriate to use the "Flag" option for this situation (given the existence of this thread). I'll keep this in mind for the future. $\endgroup$
    – angryavian
    Nov 10 '21 at 1:19
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Reopened

Three days ago, Asymptotic expansion of $\sum_{k=1}^n {n \choose k} (-1)^k \frac 1 {1-x^k} $ received three close votes due to lack of context. Since then, the author added clarification and context. Yesterday, there were two close votes arising from a review, and those closed the question. However, I think that this poster has shown a decent effort to improve their post.

The question is interesting and I request that this question be reopened.

I apologize that I forgot to mention that I have answered this question.

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Reopened

The author of Generating function of the number of permutations of length n with exactly k fixed points has added the source of the question and the solution for half of the question. I think that the question has an interesting answer and I would like to post it.

I would like to see this question reopened.

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    $\begingroup$ You could have waited a bit before the reopen review queue finishes (the second point in the guidelines) $\endgroup$ Aug 4 '21 at 19:17
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    $\begingroup$ Oops. I was involved in the OP's efforts and forgot. Sorry. $\endgroup$
    – robjohn Mod
    Aug 4 '21 at 19:24
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    $\begingroup$ This should be reopened, the justification would be that is that it follows the guidelines now. Having said that, I've seen the timeline, and please try to improve questions before formulating answers for them (I see you have created and deleted an answer and then made an improvement comment, hence this request). I know that people can get carried away with mathematical content, but please make sure that you are seeing the other side of things as well, namely the fact that you want to be making this question better(as you recognize it has site-based flaws) and then answering it. $\endgroup$ Aug 4 '21 at 19:26
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    $\begingroup$ I saw the lack of context and deleted my answer very quickly (under 2 minutes, during which time the OP was logged off). I encouraged the author to add some context, which they did. Does the presence of a deleted answer encourage PSQs? I will not undelete my answer until the question is reopened. As for when an answer is formulated, I know that once I see an interesting question, I'd have a hard time not thinking about it until the question is improved. $\endgroup$
    – robjohn Mod
    Aug 4 '21 at 20:01
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    $\begingroup$ I am happy the question reopened, but I am surprised that you wrote the answer and then noticed the issue that it was a PSQ. I think you should spot this fairly quickly and leave an improvement comment before answering the question. If you are not seeing the merits/ demerits in the question vis-a-vis the site before answering it, then I request you to be more careful and/or ask in chatrooms. $\endgroup$ Aug 5 '21 at 6:46
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Closed, Reopened, Closed by mod, deleted

This question has never been asked before on this site (nor a direct generalisation\restriction). However it was associated with two questions which each have an answer that contains a solution (or can be generalised to a solution). The question has as a result been deleted.

One of the associated questions has one answer, which has since been edited (at the request of the person who originally closed the present question) to include an argument which can be generalised to answer the deleted question. It is still not completely natural, as it does not fully answer the question it is supposed to answer.

The other question is even less related, but is slightly open ended so one of its answers included an answer to the deleted question.

In my opinion, given how simple and standard the question is, it is worth being asked and answered once on this site, even if solutions can now be dug up in two answers to other questions.

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  • $\begingroup$ For the record, there was/is in fact a 2nd dupe link (and comment) pointing to the identical proof in "other question". The common simple (2 line) proof posted in the current question is exactly the same as the proof linked in the 2nd dupe (and also exactly the same as that in the first dupe after the appropriate (obvious) specialization). There is nothing at all novel in the answer in the current question. This well-known proof has been posted here many times. $\endgroup$ Dec 6 '21 at 8:17
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    $\begingroup$ @BillDubuque If "This well-known proof has been posted here many times", then surely a better duplicate-target exists? I mean, it isn't immediately clear how to extract the answer here from either duplicate-target. Remember the links are to questions, not answers, so we have one related-but-different question (where we are supposed to notice that an incorrect answer is the one we are after), and one basically irrelevant question, where the non-accepted answer contains the relevant argument. Irregardless of the arguments being relevant, the duplicates are bad. $\endgroup$
    – user1729
    Dec 6 '21 at 9:37
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    $\begingroup$ (Of course, someone could edit this answer to point out that primality is used, or could have posted a CW answer to the question being discussed explaining the connections. But the current situation is unhelpful to anyone trying to extract this knowledge.) $\endgroup$
    – user1729
    Dec 6 '21 at 9:38
  • $\begingroup$ @user1729 Re: "extraction" Not true! When I closed it as a dupe I posted links to the answers containing the proofs. Please read more carefully before making unfounded critiques. The proofs in the dupes are exactly the same as the proof posted currently so it's not clear why you think they are "bad". All of this was already covered in comments there, so I am not going to repeat it again here. Please fully read the thread before commenting here. $\endgroup$ Dec 6 '21 at 9:46
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    $\begingroup$ @BillDubuque Sure there are links in the comments, but the main links (beneath the line "This question already has answers here:...") are to questions. I justify the badness in my comments - I do not dispute the "sameness" of the proofs, but am criticising the difficulty in extracting these arguments from the links. But more than that, I am suggesting you do something about it - don't just point at the links/answers, but, for example, correct the incorrect proof. (And I have read the thread fully.) $\endgroup$
    – user1729
    Dec 6 '21 at 9:48
  • $\begingroup$ Again, there is no such "extraction difficulty" because I gave in comments the links to the specific answers containing the proof - as I often do - to help guide the OP. $\endgroup$ Dec 6 '21 at 9:55
  • $\begingroup$ @tkf Could you please correct your post to reflect the fact that question has in fact "been closed in association with the other question", cf. the 2nd dupe link. Did you miss that? You claim you would not object so strongly if that were true, and it is in fact true. $\endgroup$ Dec 6 '21 at 10:33
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    $\begingroup$ @amWhy Thankyou for your comments. Even if no further explanation is given, I really appreciate you giving your honest opinion, and I am sorry it has gotten you berated. $\endgroup$
    – tkf
    Dec 6 '21 at 16:02
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    $\begingroup$ Regarding the above off-topic and highly misleading comments by amWhy. My comments to her simply remarked that I was disappointed that she reopened some dupes, and asked her to please be a bit more careful in reviews (we all know that they are often done too too hastily). My comments were far more polite than many of the scathing critiques that have often been placed in CRUDE. They are still there so this can easily be confirmed. $\endgroup$ Dec 7 '21 at 0:43
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    $\begingroup$ Her reply was "Apologies. All I can say is "oops". I had not payed attention in the reopen review queue". How one can go from that to the above tirade is beyond me (actually not completely so since there is a long history of such, but that is off-topic here). $\endgroup$ Dec 7 '21 at 0:54
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    $\begingroup$ I honestly don't know about this one. I am sympathetic to the idea Bill Dubuque seems to support here. That we could close questions as duplicates of an answer to a slightly different question. because the answer applies here equally well. IIRC I have pressed for something similar in the past. Then again, this is not the umpteenth replica. I could not find many other targets. I don't know if my gut feeling to let this one stay is defensible? Close the twentieth argument reuse at the slightest excuse, but require a more exact match if it is only the fifth. Doesn't sound good, does it? $\endgroup$ Dec 7 '21 at 16:11
  • $\begingroup$ @Jyrki If one works against the innate abstraction that helps to organize mathematics then any hope of organizing this site is ultimately doomed. $\endgroup$ Dec 7 '21 at 20:56
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    $\begingroup$ @BillDubuque I see you have requested that the answer to the first alleged dupe be fixed, so that it becomes a dupe for my answer. First thankyou - clearing up the incorrect mathematics is a priority. However it raises two issues. Given that my answer already exists, surely if and when the other answer is made the same as mine, it would then be a dupe of my answer, rather than the other way round? Secondly, it would not be entirely relevant, as it would address a generalisation of a restriction to the question it is supposed to answer. If duplication is to be avoided, why create one? $\endgroup$
    – tkf
    Dec 8 '21 at 2:07
  • $\begingroup$ @JyrkiLahtonen I would be happy with even one answer to a slightly different question, so if you know of any, that would resolve this. Of the two posited, the one regarding $(\mathbb{Z}_n)^*$ is very different as it does not address subgroups, and if it did the statement would be false: $1+3=4 \neq 0 \mod 8$. The answer there was given by mistake - I do not think it would be given as an answer, with the restriction to primes, given there were already complete answers there to the question asked. The other is a request for intuition about infinite sums. $\endgroup$
    – tkf
    Dec 8 '21 at 2:23
  • $\begingroup$ @JyrkiLahtonen On the other hand I do take your point about argument reuse. If it is the policy to only ever allow one instance of any given argument, regardless of the question, then I accept that of the three, your one is the one that should remain, as it is the earliest correct use of the argument. $\endgroup$
    – tkf
    Dec 8 '21 at 2:39
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Undeleted

An answer of mine to Resources, references, or examples for logics with finitely many sentences was deleted via review.

May I kindly ask to reconsider this deletion. My answer relates to the observation that finite problems are always trivial in the context of computational complexity (see, e.g., the accepted answer here). The OP requested some clarification under my post, and I would have gladly given this clarification but my answer was already deleted then.

EDIT: It seems that I could undelete the question myself and provide the clarification. Is this the recommended way to proceed?

EDIT: I took the liberty of undeleting myself.

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Re-opened.

Please reopen:

A Basic Limit From Exponentials

I believe this is not a duplicate of How does one prove that $e$ exists? which was why it was closed.

The question from the first link asks why the limit $\ \displaystyle\lim_{x \to 0} \frac{2^x-1}{x}\ $ exists. Whereas the question from the second link asks to prove that there exists a number $a$ such that $\ \displaystyle\lim_{h \to 0} \frac{a^h - 1}{h} = 1.$

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Undeleted and reopened

Please consider undeleting and reopening Is an ideal finitely generated if its radical is finitely generated?. This is a very natural question to which there are no immediately obvious counterexamples, and it has received a couple nice examples in answers.

It seems to me that this is exactly the sort of question that this site was built for: questions that may naturally occur to many people (not just some exercise that is of no particular interest), do not have obvious or "standard" answers that can be found in every textbook on the subject, and by having an answer here the answer will be easily findable with a search engine.

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Reopened

Please reopen https://math.stackexchange.com/q/4074358.

I have also voted for closing the question as a duplicate but retracted the vote after the question was edited.

It is clear from the content of the edited question that its issue was a search for an error in the OP solution (and not for a correct way of solving the problem). In this sense it is certainly not a duplicate of the linked question. In any case as soon as the link to the alleged duplicate was given OP stated that (s)he is interested only in finding the own error.

I should admit that the linked question also started with an error (a different one) and this error was not addressed in any answer (but in one of the comments).

Quite generally I would assume that the most questions aimed on search of own error (or solution verification) cannot be treated as a duplicate.

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  • $\begingroup$ After you cast the reopen vote, the post automatically went into the reopen review queue. If you wait until the review complete, you might not need to post the request here (This is mentioned in the "guidelines" of this thread"). $\endgroup$ Mar 24 '21 at 15:03
  • $\begingroup$ I agree and will next time follow the guidelines. Thank you for pointing my attention to this. $\endgroup$
    – user
    Mar 24 '21 at 15:07
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Reopened

Please consider reopening this question

Find the range of values of $θ$, such that $θ\in[0,2π]$ for which $(\cosθ,\sinθ)$ lies inside a triangle

this question is completely understandable as all the equations are now written in math JAX also it might have happened that people who were unable to solve the question have reported it. This question is from a verified text and I can prove that the question is 100% correct and it's the case of false reporting.

At last, I request once again to please consider reopening this question

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Undeleted

Please consider undeleting this meta post.

I don't have enough reps to see the post now, so I might miss the reason why the OP deletes the post. But the question they ask are quite legit and there are some useful discussion in the comment.

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  • $\begingroup$ Hmm. I’m not so sure if I should vote to undelete as it was deleted by OP themselves. (In general I use far fewer review type votes on meta...) I guess it was due to the overall negative reaction. If you want I can copy the comments somewhere, if you wait for me to reach a computer $\endgroup$ Jun 30 '21 at 9:12
  • $\begingroup$ Thanks, @CalvinKhor It's not that I particular want to see the discussion again. I just feel that that is a good question to ask (it's a shame I had to downvote it) and the discussion there should be useful to stay. $\endgroup$ Jun 30 '21 at 11:00
  • $\begingroup$ Well, here is the discussion anyway: imgur.com/a/kWBXfYN as you can see, there is one undelete vote atm. $\endgroup$ Jun 30 '21 at 11:05
  • $\begingroup$ You could of course ask the question again yourself? $\endgroup$
    – user1729
    Jul 2 '21 at 8:54
  • $\begingroup$ @user1729us yes, but the discussion is already there. $\endgroup$ Jul 2 '21 at 11:51
  • $\begingroup$ I've voted to undelete because it's worth resuming discussion on this topic. $\endgroup$
    – Toby Mak
    Jul 22 '21 at 11:24
1
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Undeleted, deleted (by Community user, as "abandoned")

Please undelete Group theory question of red and blue blocks as the question asker has self-deleted his/her own question a few hours after receiving an answer from a trusted user.

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    $\begingroup$ Trusted users should be trusted not to answer copy-paste homework questions. $\endgroup$ Jan 26 '21 at 3:46
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Reopened

Please consider reopening If the image of an operator is closed, is the image of the powers of the operator also closed?. This is a very natural question to which there are no immediately obvious counterexamples, and it has received a very nice answer.

It seems to me that this is exactly the sort of question that this site was built for: questions that may naturally occur to many people (not just some exercise that is of no particular interest), do not have obvious or "standard" answers that can be found in every textbook on the subject, and by having an answer here the answer will be easily findable with a search engine.

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    $\begingroup$ If a link to a question reveals it to be closed, will it remain closed? :) $\endgroup$
    – amWhy
    Dec 15 '21 at 15:51
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    $\begingroup$ To be honest : for this question, I think you can consider a context rewrite if you are interested. For some context : this post shows that if $T$ is compact with closed range then the range is finite-dimensional. Now, if $T$ is compact, so is $T^n$ for any $n \in \mathbb N$ (product of compact operators remains compact) : therefore, $T^n$ also has finite-dimensional and hence closed range. Right now , I think it should remain closed, but looks good for a context rewrite. $\endgroup$ Dec 15 '21 at 17:23
  • $\begingroup$ Minor correction to the above : if $T$ is compact with closed range then $T$ is finite dimensional, so $T^n$ is finite dimensional (don't need to use any product-compact results) hence has closed range. $\endgroup$ Dec 16 '21 at 7:31
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Re-opened.

Please reopen Less common probabilities and expected values related to the coupon collector problem. It is falsely closed as a duplicate. Though the question brought in the title is indeed very often it is not asked in the body of OP.

Particularly the question asks about the expected value of collected unique cards after a certain number of trials, not about the expected number of trials to collect a certain number of unique cards. Though the former question is probably have been already asked and answered here, it is certainly not that one which was linked as "original".

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    $\begingroup$ What you say about not being a duplicate is true, but this is so because the OP asks multiple questions. By itself that is not a fatal flaw (the problems are closely related), but the Question provides no context. It appears to me to be a "pass through assignment". If you like the Question enough, perhaps leave a comment for the new user to provide context, or repost the problem with your own context. $\endgroup$
    – hardmath
    Feb 10 '21 at 16:46
  • $\begingroup$ @hardmath OP indeed asks multiple questions. But none of the questions is asked or answered in the alleged "original". I would not complain if the question was closed because of "providing no context". This would stimulate the author to correct it. But the given link certainly will not help him or her to find the correct answers. $\endgroup$
    – user
    Feb 10 '21 at 16:52
  • $\begingroup$ @hardmath That would be great. $\endgroup$
    – user
    Feb 10 '21 at 17:01
  • $\begingroup$ After a bit of research I chose one of the coupon-collectors Questions that asks about the probability distribution aspect, and which not only has a decent Answer but also links to many other Questions of a similar nature. Of course the expected value problems are easier than working out the probability distributions (after $x$ cards bought), but the OP has done literally nothing to motivate writing out a new Answer. $\endgroup$
    – hardmath
    Feb 10 '21 at 23:57
  • $\begingroup$ @hardmath The given link is of course very interesting but it does not address the asked questions, neither do the links inside. Though I agree that it can help to point out the direction (if the asker has a solid background). $\endgroup$
    – user
    Feb 11 '21 at 8:43
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Undeleted, reopened, reclosed (as duplicate)

Yesterday I posted this this question. When I checked it last night, it had the two sound-looking answers you see. I woke up today to find it had been not just closed but completely deleted. This seems to me completely preposterous. It's pretty clearly not a homework question, but a reasonably deep integral computation that I had no idea how to begin. I'd be happy to provide more "context" (1. unnecessary though that evidently was for the people who answered it, and 2. as if the identity isn't interesting in its own right) but the post is completely deleted and so I was given no opportunity to do so in anything like this site's notion of a timely manner. Is there some way I may be allowed to provide the all-important context in order to reopen the question so that I can at least reward the people who helped me?

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    $\begingroup$ So you can just go to the deleted question (which you can get to from deleted recent questions in your profile) and copy the address from there an users with >10K rep can view it and possibly vote to undelete it. Posting an image here with no link makes anyone but a moderator unable to help you. $\endgroup$ Mar 31 '21 at 23:37
  • 1
    $\begingroup$ @MattSamuel I see, thanks. I've added the link $\endgroup$ Mar 31 '21 at 23:56
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    $\begingroup$ Can't you edit the deleted post? Asking for undeletion before improving your post (and not mentioning the fact that there's a linked duplicate in the comments) seems premature. $\endgroup$
    – KReiser
    Apr 1 '21 at 0:16
  • 1
    $\begingroup$ still seems a bit of a shame that the very nice answers will be lost $\endgroup$ Apr 1 '21 at 0:37
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    $\begingroup$ just for the record though, it is as i thought -- i get the "This post has been deleted -- no more edits are allowed" when i try to edit it. @KReiser $\endgroup$ Apr 1 '21 at 0:40
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    $\begingroup$ The post has been undeleted (it is still closed. Perhaps it should be better closed as a duplicate) $\endgroup$ Apr 1 '21 at 1:50
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    $\begingroup$ Thanks you for improving the question - it is much better now. I voted to both close and delete this question at the time because it was simply the statement of a question without any context or effort or anything. I would have acted similarly if you had been a new user, but my actions were particularly heartfelt because you are not a new user, and instead have been here for almost 10 years and have picked up 5k rep. points. So you surely must have picked up on what is expected of a question by now... $\endgroup$
    – user1729
    Apr 1 '21 at 10:00
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    $\begingroup$ @user1729 I don’t know if this is the proper place to discuss this, but since you’ve made the same comment twice now I’ll respond by saying that I and a non-negligible minority of other users of the site don’t share your expectations that a post contain “context” or exhibitions of failed attempts when those things aren’t likely to help people answering it. My post is a good example. You say the post is now “much better,” but I think you’d be hard pressed to explain how what I’ve added about resolvents of Brownian motion would make it easier for someone to help me. $\endgroup$ Apr 1 '21 at 10:34
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    $\begingroup$ @Timkinsella Its not about someone being better able to help you, per se, although you have now given the book where they could look it up in (which is helpful when people misquote a problem, or the problem requires a result proven earlier in the book, etc.). There are other reasons for providing context too, including basic politeness, but also: We live in a world where the vast majority of exams are not in exam halls (for example, my uni has 24 hr take-home exams), so giving some context and providing some effort stops your question getting lumped in with the obvious cheaters. $\endgroup$
    – user1729
    Apr 1 '21 at 10:43
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    $\begingroup$ That is totally leaving aside your decision to vote to completely delete the question so soon after it was asked for the reason that it lacks context, a reason that calls for the OP to improve the post which he cannot do when the post is deleted @user1729 $\endgroup$ Apr 1 '21 at 10:49
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    $\begingroup$ @Timkinsella Sure. I would have been more lenient if you hadn't been here for almost 10 years with lots of rep. points. $\endgroup$
    – user1729
    Apr 1 '21 at 11:04
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    $\begingroup$ As one of the original close voters I should probably declare that I had the exact same thought process regarding voting to close. There so many questions that it's not effective for those that "stand on their own merits" to be vetted for quality by non-experts (e.g. experts in other fields), and the close voting is democratized. Writing for Math.SE is different from writing for a book. If you think there is a better (and scalable) alternative to separating the wheat from the chaff other than adding context, you should try to post a question on meta to persuade the majority. $\endgroup$ Apr 3 '21 at 5:58
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    $\begingroup$ @CalvinKhor If “wheat” = “questions that very probably didn’t come from a freshman calculus exam”, then I don’t really know what level of expertise you’re talking about. Behind this fixation on “context” and documentation of failed attempts I see no actual criteria for judging the quality of questions beyond an extremely crude correlation with the mere length of the post. $\endgroup$ Apr 4 '21 at 6:03
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    $\begingroup$ For instance, I wonder how a user might ask the same question I asked if it were merely posed to him, with no context, by a classmate? He has no context to offer you; are you going to believe he’s a curious student asking in good faith? Or are you going to fire off a passive aggressive comment about effort and expectations and delete his post? Seems like a tough choice if you’re philosophically opposed to actually thinking for a few moments about questions before you judge their quality. $\endgroup$ Apr 4 '21 at 6:14
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    $\begingroup$ @user1729 Frankly I wonder whether that’s true, and not just because you explicitly said the opposite in your first comment above. $\endgroup$ Apr 4 '21 at 6:33
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Reopened

I'm not sure why this question was closed. I feel like the OP is maybe slightly unclear about what possible methods there might be for finding the coefficients, but the problem they are trying to solve is clear and answerable (It is upvoted and has an accepted answer (Disclosure: The accepted answer is mine).

Can we determine higher powers of a matrix in terms of lower powered matrices?

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Reopened

Please consider reopening Example of a map of coverings which is not a covering map, if the base space is not locally path-connected. This is a natural question asking for an example to show that a certain technical hypothesis is needed in a well-known basic theorem in the theory of covering spaces. The original version of the question was missing a crucial assumption and as a result didn't make much sense, which I believe was the reason the question got its first few close votes.

It seems to me that this is exactly the sort of question that this site was built for: questions that may naturally occur to many people (not just some exercise that is of no particular interest), do not have obvious or "standard" answers that can be found in every textbook on the subject, and by having an answer here the answer will be easily findable with a search engine.

[Disclosure: I have answered the question.]

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    $\begingroup$ Actually I was about to post the request, and you are correct in evaluating my close vote there. $\endgroup$ Jul 20 '21 at 16:52
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Reopened

I come here for this question.

The background of this question is as follows : it initially contained a single supporting statement along with the problem statement. It was closed , then the author edited the question to reflect their surprise at the closure and mention that the question arose from idle curiosity (i.e. sufficient context was , in my opinion, not added). This edit fetched reopen votes until it was rolled back, by which time it had opened again.

However, the post had been revised post-reopening : the setting of the problem is clearer to see, and the level of answer required has been clearly emphasised, as has the source of being an "idle curiosity" (we can argue over if it counts or not). So that's source (I take it to be a honest admission) and background/type-of-answer-sought sorted. It has now been closed again, however.

I would like the post to be judged on its current merit for the purpose of reopening. I would also like people to debate if context rewrites are required for this question or not, and what content will be suitable for this (Note : the page for admissible context rewrites is here and my opinion is that the setting and the problem statement could do with a link statement).

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    $\begingroup$ Poor judgement here, Teresa. $\endgroup$
    – amWhy
    Sep 25 '21 at 17:01
  • $\begingroup$ @amWhy All my reopen requests here (with probably one exception way below this if I'm not wrong) were made in poor spirit and with the intention of trying to clarify what was wrong with some posts which I felt were not wrong. All of them got clarified on CURED. I'm not sure I will be doing this again, but I'll have to work hard to gain your confidence in this statement. $\endgroup$ Sep 25 '21 at 17:32

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