Requests for Reopen & Undeletion Votes (volume 07/2018 - 12/2020) [duplicate]

The purpose of this thread is to help 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 this thread that served as a model:

• I edited the post inspired by a concern expressed in a comment. – quid Mod Jul 19 '20 at 23:49

189 Answers

Undeleted, reopened, closed as duplicate

Please consider undeleting this well-received (33 net upvotes) question under the tag of probability: Probability of drawing the Jack of Hearts?

There are useful discussion and several good answers, one of which has 77 upvotes.

• The question was originally closed as "off-topic: lacking context" (which, in my opinion, was not unreasonable). It is, however, also a duplicate of other questions, as indicated by the comments. If it is to remain on the site, it should be properly linked via a dupe closure. – Xander Henderson Mod Aug 19 '19 at 17:38
• At most "similar" or "related". Not a duplicate. – user9464 Aug 19 '19 at 17:54
• I'm sorry, but what? The question above asks us to determine the probability of drawing a Jack from a deck of cards from which an unknown card has been removed. One of the two questions in the dupe target asks for the probability of drawing an Ace from a deck of cards from which an unknown card has been removed. These are precisely the same question, and answers to the older question completely answer the newer question! How is this not a duplicate? – Xander Henderson Mod Aug 19 '19 at 18:32
• Mr. Henderson, I have a very narrow definition of "duplicate" from yours. No need to be sorry. And of course you do have the right to vote it as a duplicate. – user9464 Aug 19 '19 at 18:34
• I marked it as a dupe. That said @Xander I think the difference is slightly larger than you make it look. This question is about one specific card (a jack of hearts), while the dupe is about a group of cards (an ace). I still think that is a duplicate. // Since the comment on main got auto-deleted I'll add that two users other than me had mention it as a dupe. Thus, it was at least a trilateral closure. :-) – quid Mod Aug 19 '19 at 18:54
• @quid Indeed, I had missed that. That said, as you note, the distinction is not fundamental. Thank you for handling it. – Xander Henderson Mod Aug 19 '19 at 19:39

The question Problem with sum of projections was incorrectly marked as a duplicate of Orthogonal projections with $\sum P_i =I$, proving that $i\ne j \Rightarrow P_{j}P_{i}=0$. The latter question has the additional hypothesis that the projections are self-adjoint (i.e., orthogonal projections) which allows for some rather different proof methods. Indeed, none of the four answers to the second question solve the first question.

Deleted, undeleted, deleted, undeleted, deleted, undeleted, deleted, undeleted and reopened

unfortunately the question I asked Why is the zero polynomial the only one to have infinite roots? was put on hold as off-topic first and then closed. I edited it much for it to be reopened but it wasn't opened. I apologise if it was off-topic to you, but I edited it. If it being off topic yet, kindly suggest improvements or reopen it.

• Please include a link to the question. – quid Mod Feb 3 '19 at 14:54
• its humble request – user629353 Feb 3 '19 at 14:56
• why you deleted that – user629353 Feb 3 '19 at 14:58
• @quid couldn't you suggest edits – user629353 Feb 3 '19 at 15:03
• "couldn't you suggest edits " What do you mean? How am I supposed to know which question you mean? – quid Mod Feb 3 '19 at 15:05
• @quid the link of which i have given above – user629353 Feb 3 '19 at 15:09
• I misunderstood what you meant. I did not delete you question. At the moment I do not plan to get involved. – quid Mod Feb 3 '19 at 15:46
• Two posts here about the same question. Are we supposed to expect some more any time soon? – Did Feb 3 '19 at 21:39
• @Did, the first post was about closure, the second, deletion. Unless there is some action more severe than deletion, I'd guess there won't be any more posts about the question. – Gerry Myerson Feb 3 '19 at 21:52
• I have flagged the question on main to ask the moderators to let the community make the decision. – Gerry Myerson Feb 5 '19 at 11:48
• The main problems with the question seem to be that (i) the questioner is confused, and (ii) it's tricky to answer in a way that properly addresses the confusion. The first seems a good reason to ask the question, and the second suggests that good answers will be thoroughly explanatory and therefore of high value. – timtfj Feb 5 '19 at 16:05

Reopened

I asked a question yesterday: Coupon collector's problem: mean and variance in number of coupons to be collected to complete a set

This asks for the mean and variance of the coupon collector's problem in the general case when the coupons have unequal probability. It has been marked as a duplicate of this one: Expected time to roll all 1 through 6 on a die

My edit clearly explains that I'm asking for the variance in the general case, while the question it is a supposed duplicate of asks only for the mean and that too in the special case of the coupons having equal probabilities.

So, the first question is not a duplicate of the one linked to it for sure. For this reason, I wanted the duplicate tag to be removed if possible.

I did ask a similar question myself in another post a few weeks ago here: Coupon collectors problem: variance calculation missing a term.

However, I wish to delete that post (the only answer there is my own) and want people to refer to this one since it is much more comprehensive.

In any case, the current question linked there is clearly more limited in scope along multiple dimensions.

• I suggest that in the interests of transparency you edit a link to your earlier question into the body of the newer question, and vice versa. – Gerry Myerson Nov 28 '19 at 21:25
• @GerryMyerson I'm going to delete the other question, so this might not be necessary. – Rohit Pandey Nov 28 '19 at 21:34

Reopened

Request to reopen Derive an atlas of Monge patches for a surface in 3D

Since the votes to close (without any comments), I've added links to sources and multiple links to material that motivates the question. I've also clarified what would constitute an answer to the question.

Undeleted

I'd be glad if my question Operator characterizations of continuity and “co-continuity” was undeleted. It was automatically deteleted after one year since there were no answers, no comments and no votes. Recenly I wanted to reference the question in another answer and it was very hard to find it (see my post on Meta for more details). I think the question itself is written well enough and that it contains a useful summary.

• If the question doesn't generate some activity, then presumably it will be auto-deleted again somewhere down the track. – Gerry Myerson Feb 15 '20 at 21:38
• @GerryMyerson Hopefully, that would happen no sooner than in one year, so there is chance to get some activity. In fact, it got an upvote after the undeletion. – user87690 Feb 15 '20 at 22:17

Undeleted, reopened

Please consider undeleting Complex Analysis: Showing analytic function is zero .

The post itself might be a PSQ and a frequently asked one at that (I guess that is because an easier version of this Privalov's Theorem is an exercise problem from Stein and Shakarchi's Complex Analysis textbook) but there are some good answers with valuable insights that are not 'textbook' in my opinion.

P.S.: The exercise from the book additionally assumes the holomorphic function converges uniformly to $$0$$ on the portion of the arc. For example see

• Is this the exercise from the book, or what is the exercise in the book? – quid Mod Apr 5 '20 at 21:58
• The exercise asks the same problem but with additional condition of the function being continuous upto the boundary of the disk. – r9m Apr 5 '20 at 21:59
• Could you edit that into the post as context? (Or maybe you cannot as it is deleted. In which case I ask would you if undelted.) – quid Mod Apr 5 '20 at 22:03
• @quid If the post is undeleted can I put a link of this post in the question? – r9m Apr 5 '20 at 22:25
• I prefer if the relevant context is put into the actual post, you can link to the discussion here in a comment. (Generally As a rule, no "meta" content in a post. If it need be there can be a comment.) – quid Mod Apr 5 '20 at 22:31
• Now undeleted. Please edit as indicated previously. – Gerry Myerson Apr 5 '20 at 22:49
• Voted to reopen still need a vote to reopen the topic. – MtGlasser Apr 5 '20 at 23:26

Reopened

It was closed for the understandable reason that it lacked sufficient detail to be comprehensible by someone without Rudin's book to hand, and not only that, the reference to the book was inaccurate! But the poster, a newcomer, has carefully edited the question to provide more detail, and to correct the erroneous reference. Then, after waiting for five days, he asked politely if there was anything more he needed to do. Meanwhile, another poster had provided full details in a comment - whose length even provoked some controversy!

I don't think anything more needs to be done (unless someone with moderator privileges wants to edit the comment into the question).

The question has two reopen votes already.

• You certainly have those moderator privileges to edit the question, if you want to do that yourself. I also believe the length isn't the problem with that comment, but the fact that it contains those superfluous "begin quote" and "end quote". Perhaps by flagging a moderator is willing to edit that out, since otherwise it's an useful comment. – Zacky Apr 17 '20 at 15:13
• @Zacky Thanks for editing the question. – Calum Gilhooley Apr 17 '20 at 15:53

https://math.stackexchange.com/questions/2659982/does-the-law-of-cosines-contradict-pythagorass-theorem

This question was undeleted by 10 people then subsequently deleted and locked by a moderator. I request that such a heavy handed, unilateral action be undone since clearly many people disagree.

• Also the subject of math.meta.stackexchange.com/a/30914/8269 – Gerry Myerson Apr 27 '20 at 9:44
• Very poor post that is thankfully deleted. You should have considered keeping this poor answer deleted as well, @Matt. – amWhy Sep 9 '20 at 22:59

Undeleted

As you see, some users have done serious contributions in order to solve the conjectured problem, so it may be unfair to permanently delete the whole discussion. My own attempts to solve the questions were fruitless.

Undeleted, Reopened

Please undelete and reopen If $$AB\parallel DC$$, $$BC\parallel AD$$, and $$AC\parallel DQ$$, find $$\Bbb X$$ in terms of the areas $$\Bbb A$$, $$\Bbb B$$, and $$\Bbb C$$. (the asker showed attempts as discussed in the META question here). More context has been added.

Let it be known that I answered the question. This information seems unnecessary. My answer is there when you open the link (and you have to, if you want to decide whether to reopen/undelete the question). Why do users insist on having this information disclosed, even if the information is public? Whether you want to reopen/undelete a question should depend on your opinion on the question and answers there, and not on the person who asked the question or who answered the question.

• We note that user Batominovski has posted an answer to the question. – Gerry Myerson Jul 4 '20 at 6:52
• @GerryMyerson I am not sure why this seems to be an issue. Many users here also requested questions they have answered to be reopened/undeleted. I can make my answer a community wiki post if that is a problem. – Batominovski Jul 4 '20 at 6:58
• No need to go community wiki, just be transparent when you have an interest in a question, please. – Gerry Myerson Jul 4 '20 at 7:11

Reopened

I tried my best to edit this question to make it more concise, if anyone has recommendations on how to make it even better pls just ping me

Why do sometimes care for where vectors originate from and sometimes not? and exactly how many kinds of vectors are there?

Undeleted

May I request that this old question Countably Infinitely Many Points in a Euclidean Space of mine be undeleted? The deletion was done by an automatic system (if that is the case, can it be voted to be undeleted?). I am certain that the question is well written with a lot of context. I would like to put a bounty on the question.

I request that my question here is reopened:

Do I understand the difference between $\implies$ and $\to$?

I ask some very specific questions about the use of $$\implies$$ and $$\to$$ that it is different from the duplicate question.

• I suspect it would help your case if you edited your question to remove anything covered by the linked question, and also to made clear the differences between your question and the linked one (whilst still making the question readable, etc.). This would make it easier for people to judge the differences. – user1729 Sep 1 '20 at 9:15
• @user1729: I can do that. I just wanted to give the context that I was working in. – John Doe Sep 1 '20 at 13:41

Reopened and Undeleted, Closed again, Deleted, Undeleted, Deleted again

I think the following question should be reopened: What Are The Elements of $$e$$ in Set Theory?

It is an intriguing question which is no less deserving of attention than many of the questions we get here (I'd rather this kind of conceptual question than yet another integral to solve). It seems to me that the issue with the question is that it is not well-posed (to quote Asaf's answer, the answer "depends on which set is $$e$$"). However, the answers are explain the issue with the question and how to resolve it, which is the kind of answer I think the question needs.

• Maybe the question is not that bad as it has elicited nice responses from various well established users. But the asker is not really keen on learning from the responses, and perhaps not really clear about their purpose in asking the question. It should be closed as "needs clarity". If the questions includes some proper context about definition of $e$ as well as its representation then it is more likely a candidate for reopening. – Paramanand Singh Sep 1 '20 at 12:04
• @ParamanandSingh I disagree. It is clear that their purpose is that they wished to understand a comment of Asaf from elsewhere. One of the key points in the answers, and one of the subtleties of the question is that it matters how we define $\mathbb{R}$, so asking the OP to clarify this undermines this. Also, I don't think we should be judging the question based on the user, or their comments to the question; indeed, if we ignore the comments then everything is nice. – user1729 Sep 1 '20 at 12:50
• I am not judging users, the question does require a bit more clarity, for example what particular definition of reals is being used. A link to Asaf's comment on which this is based should also be included. Is the asker familiar with the set theoretic development of number systems or not? – Paramanand Singh Sep 1 '20 at 15:06
• Had these points been included in the question I think it would have been received very differently. – Paramanand Singh Sep 1 '20 at 15:10
• It is hard to believe the question is honest given the comments left in some of the answers. – Andrés E. Caicedo Sep 14 '20 at 19:53
• @AndrésE.Caicedo I don't think we should be judging the question based on the user (who has a reputation for crankery), or their comments to the question; indeed, if we ignore the comments then everything is nice. – user1729 Sep 14 '20 at 20:39
• @ParamanandSingh I learned from the responses that there exists more than one possibility for the elements of e, and it's cardinality. I didn't realize that before I had asked the question. I asked about how they could all represent the same set, since once set doesn't have two cardinalities. I didn't get a response to that, and one person apparently wanted no learning about the cardinality of e. Perhaps my incorrect assumption was that there was one unique set theory, when there exist multiple set theories with conflicting concepts of e. – Doug Spoonwood Sep 15 '20 at 13:29
• @DougSpoonwood: I am not an expert on set theory so can't really say much here. Perhaps you should add all such clarification as a part of your question. – Paramanand Singh Sep 15 '20 at 14:12
• @DougSpoonwood The point is that the "cardinality of $e$" doesn't matter, because its elements however you define is as a set mean different things depending on the definition. If you define it as a Dedekind cut, it is the set of all rationals less than $e$ and countable, and if it's as an equivalence class of Cauchy sequences then it's uncountable, but you can't compare the two sets by looking at their elements because it isn't meaningful. Equality has to be taken in a broader sense here as not meaning exact set-theoretic equality, but rather equivalence. Different sets, same real number. – Matt Samuel Sep 15 '20 at 23:06
• @Doug: Your comments here seem almost dismissive of set theory, as something that you expected to be somehow "unique" but isn't. But again, go back to my answer, and actually read it. Are you surprised that there are different browsers (which in the past were almost incompatible with one another), or that there are different banks, different shops, or different operating systems? But if you want to buy a shoe online, which shop and which bank you use, and which delivery company does the actual delivery turn out to matter less to the end result of you having a shoe. – Asaf Karagila Mod Sep 16 '20 at 11:18
• @AsafKaragila I've started a sandbox for a "canonical" form of this question here, as mentioned in the comments to the question. Feedback (from anyone!) is appreciated. – user1729 Sep 16 '20 at 13:07
• @AsafKaragila No, I'm not surprised by different browsers, different banks, or different shops. But also, there isn't a presentation of all those things as if they were one, unitary entity. The end result from purchasing things can differently significantly with respect to real world products. – Doug Spoonwood Sep 16 '20 at 15:54
• @Doug: Nobody presents constructions of the real numbers in set theory as "this is the only way to do it". – Asaf Karagila Mod Sep 16 '20 at 15:55
• @AsafKaragila It does seem to me, and perhaps this is my mistaken impression, that set theory, or at least ZFC (yes, I know there exists other choices like Von Neumann's), gets presented as a single theory for mathematics. It doesn't seem so when talking about how just one real number might get constructed. – Doug Spoonwood Sep 16 '20 at 15:59
• @MattSamuel "Equality has to be taken in a broader sense here as not meaning exact set-theoretic equality, but rather equivalence. Different sets, same real number." I've been assuming that for all x, where x is a number, x = x. I don't see how equality fits here, because of the inequality of different construction of 'e's. I have to wonder if non-standard models might come into play here somewhere, given that x = x, gets suggested by one e having different members than another e. – Doug Spoonwood Sep 16 '20 at 16:08

Closed, Deleted

I believe https://math.stackexchange.com/questions/3644075 should be reopened (despite the bad title). It asks how to locate a a mathematical paper but was closed as “not about mathematics”. Reference requests are allowed – this is not a reference request, but the intention behind seeking a reference and seeking to locate a known reference is essentially the same; I see no reason why one should have its own tag () and the other should be off topic.

• The question is though is the question to locate the reference or is the question to get the document delivered. The former is maybe borderline on-topic, the later is off-topic, and indeed not about mathematics. – quid Mod Apr 26 '20 at 10:01
• It is also not clear from the question whether the OP looks for the original or they want to know about existence of English translation. The tags (reference-request) and (translation-request) might be suitable there. – Martin Sleziak Apr 26 '20 at 10:02
• @quid: How do you mean, "delivered"? Do you mean the question could be interpreted as asking for someone to send them the paper? I would take "seeking" to mean that they would like someone to point them to where to find it (in an archive, in a collection, ...). – joriki Apr 26 '20 at 10:05
• Yes, that's what I mean. (If "send" includes provide a link to a download.) Having looked at the edit history I agree with @MartinSleziak that the intent of the question is rather unclear. Maybe it could be on-topic but as is it's unclear what even is asked. – quid Mod Apr 26 '20 at 10:10
• @quid: But what's off-topic about seeking a link where one could download a paper? How is a link different from a reference? They're both resource locators. Where else would a person be on-topic asking where to find a math paper if not here? – joriki Apr 26 '20 at 10:12
• @quid: I posted that before seeing the edit to your comment. If it's unclear, it should be clarified, or at most closed as unclear; then the OP can clarify it and get it reopened. Currently the close reason is telling the OP that questions about locating papers (or translations thereof) are not welcome here, which would be news to me. – joriki Apr 26 '20 at 10:17
• The question is what does "locating" mean in your comment. Typically with an exact reference it is trivial to locate a version of the document. Yet to access them might cost time and/or money, and helping with the last step is not about mathematics. – quid Mod Apr 26 '20 at 10:24
• @quid: What are you basing this on? I can't find any related policies. You're dividing locating resources into steps and defining some of the steps as off topic and others not. But finding a way to download a paper somewhere is just as much or little about mathematics as finding a classical reference to it. Being trivial is different from being off-topic. Lots of uncontroversially on-topic mathematical questions on the site are trivial. – joriki Apr 26 '20 at 10:30
• Common sense. But actually it also did come up I think. And to elaborate on the "common sense" providing service to access documents given a reference is a service that is provided. The people that provide it are, eg, librarians, often without any particular competence in the subject of the paper but instead in well providing access to the literature. – quid Mod Apr 26 '20 at 10:35
• @quid: OK, that's a criterion that makes sense to me. So the question would be off-topic if it asks for a service that doesn't benefit from mathematical expertise (and could in fact perhaps be performed better by a librarian than a mathematician), but would be on-topic if if benefits from mathematical expertise? That distinction would not always be clear-cut (mathematicians probably know their way around some online math resources better than librarians), but it would be a sensible explication of what it means for a reference request to be "about mathematics". – joriki Apr 26 '20 at 10:39
• @quid: I see. I think that's a bad tradition. Perhaps I'll write a post about that some time. – joriki Apr 26 '20 at 11:07
• @quid: Speaking of tradition: It seems that in the olden days people were more willing to act as mathematical librarians. This question and its several answers have lots of upvotes and no downvotes; the answers provide both general advice on how to locate papers and specific links for the specific search that prompted the question. Interestingly, one of the answers is by amWhy, these days not a stranger to advocating for closure as off-topic (and, incidentally, for leaving incorrect close reasons in place). – joriki Apr 26 '20 at 11:17
• @quid: On your previous comment: Yes, I was aware of that difference, but that difference doesn't make a difference with respect to the one thing we agreed on above, that a sensible criterion for being on topic here is whether mathematical expertise is beneficial for answering the question. If mathematicians are particularly competent to give advice on methods in general, then they're also particularly competent to help in finding specific papers. – joriki Apr 26 '20 at 11:38
• @quid: On what are you basing the implication that questions shouldn't be encouraged that are not of interest beyond the immediate need of one person? Lots of uncontroversially on-topic questions are like that. – joriki Apr 26 '20 at 11:39
• Since you care about the old days, certainly you still recall "too localized". – quid Mod Apr 26 '20 at 11:41

Undeleted, re-deleted, re-undeleted, closed, deleted again

Before I could upvote this answer, the question asker self-deleted her question. That's an abuse of the platform. Please undelete.

• If you can still access the question, you could flag it for moderator attention. – Gerry Myerson Nov 26 '20 at 21:29
• @GerryMyerson Thanks for suggestion. I've done so. – GNUSupporter 8964民主女神 地下教會 Nov 27 '20 at 23:25

Reopened

2 reopen votes left please:

Prove $\lim_{z \rightarrow z_o} f(z) \in \mathbb{C}$ if $\lim_{z \rightarrow z_o} (z-z_0) f(z) = 0$

I made a new question, where I tried to be as clear and narrow as possible.

Reopened

There have been at least five questions asking how to prove instances of the general proposition $$\log_m(m + 1) > \log_n(n + 1)$$ for integers $$n > m > 1$$:

1. How to know if $$\log_78 > \log_89$$ without using a calculator? (3 May 2012), with an exemplary answer by user22805.

There have been at least three other questions asking to prove inequalities of the form $$\log_a{b} > \log_c{d}$$ for integers $$b > a > 1$$ and $$d > c > 1$$:

There has also been at least one more complex question in the same broad category:

Most recently, the following question was posted, but it was quickly closed as a duplicate (I confess to being one of those who voted to close it):

10. Comparing logarithms with different bases (23 Oct 2018).

The close message for question 10 reads:

This question already has an answer here: How to compare logarithms $$\log_4 5$$ and $$\log_5 6$$? 6 answers

But the only method used to answer a previous question (1-9) that can also be applied to the present question (10) is to find positive integers $$m, n$$ such that $$b^n > a^m$$ and $$d^n < c^m$$ (as in Eudoxus's theory of proportion), so that $$\log_ab > \tfrac{m}{n} > \log_cd$$.

In a comment (which has now been incorporated into the text of the question), the questioner showed that he was aware of this method, and had already used it to answer his own question. He continues:

However, that method doesn't work for every example, and I wonder if there's a easier way to solve this?

Strictly speaking, any logarithm comparison question could be answered in this way. But that is not always very practical, because one one has to search for suitable values of $$m$$ and $$n$$, which may be quite large. Some previous answers state or imply the general rule that $$\log_a{b} > \log_c{d}$$ if $$\tfrac{b}{a} > \tfrac{d}{c}$$ and $$a < b$$, but that rule does not apply in this case. It is interesting to ask if some other rule might be applied, eliminating the need for a possibly haphazard search for $$m, n$$. Failing that, ad hoc solutions to the present problem are also of interest.

Question 10 meets MSE's selection criteria, so it ought to be reopened.

• The question lacks contract in any event. Most importantly: why were the specific constamts in the problems chosen? If the problem is about arbitrary constants, it should be rewritten to say so. If the OP was already aware of a method to solve the problem, that context should also be in the post. Overall the post does.noy seem to demonstrate much effort to write a good post. – Carl Mummert Oct 28 '18 at 16:19
• @Carl On that basis, Diophantus would have a hard time posting a question here! Where, in MSE's rules, does it say that every question must be framed in the most general terms possible? What is wrong with asking a question about particular numbers? Especially as no-one has (yet) posted a general answer or a general question covering this particular case. Finally, even if it were granted (purely for the sake of argument) that an experienced user ought to have asked a more elaborate question, shouldn't a new user be cut some slack? – Calum Gilhooley Oct 28 '18 at 16:28
• @Carl Also, it was closed as duplicate, and my point is that it is not a duplicate. The close message is a false statement, and the close decision should be reversed. (Of course, anyone can also vote to close it for another reason, and no such person need feel obliged to vote for reopening.) – Calum Gilhooley Oct 28 '18 at 16:34
• !Calum: there's no problem posting a question with specific numbers - but it is up to the OP to include adequate context, and the reason for choosing seemingly arbitrary numbers is (in my opinion) part of that context. If this was asked person to person at a department tea, we would expect the asker to say something about the numbers involved. The OP should be encouraged to improve the problem, they have plenty of "slack" to do so. – Carl Mummert Oct 28 '18 at 21:19
• I think my guilty conscience over this has now been assuaged. :) – Calum Gilhooley Oct 29 '18 at 0:36

Can this answer (on permutation groups) be undeleted:

https://math.stackexchange.com/a/3197094/10513

It was deleted for not providing an answer to the question. However, it gives a decent hint which leads to a solution. The hint is essentially "consider odd vs. even numbers". This was made formal in the accepted answer, which used mod 2.

• I think it's a bit of a stretch from that hint to the accepted answer. The hint ought to be a comment (in my opinion). – Gerry Myerson Apr 29 '19 at 12:50
• @GerryMyerson Hints are a grey area. But I don't think deleting them because they are "a bit of a stretch" is the right thing to do. – user1729 Apr 29 '19 at 12:55
• It would have been better, had a moderator converted the "answer" to a comment. You could try flagging the question for moderator attention, and making that suggestion. – Gerry Myerson Apr 29 '19 at 12:59
• I flagged it beforehand, and was told to post my request here (admittedly i didn't suggest making it into a comment) – user1729 Apr 29 '19 at 13:19
• OK, now you know what to do. – Gerry Myerson Apr 29 '19 at 13:22

Undeleted, redeleted, re-undeleted, reopened

Please consider reopening the following question:

O is a point in triangle ABC. OA, OB and OC are joined and produced to meet BC, AC and AB at D, E and F. Find the value of OD/AD+OE/BE+OF/CF.

OP clearly indicates his/her attempt in the post:

I took the special case when O is exactly in the centre of the triangle and got the answer $$1$$. But how can I prove it by taking the general case?

This is not a zero effort question.

• Question was not merely closed, but deleted. Now undeleted (but still closed). – Gerry Myerson Apr 27 '19 at 0:26
• It's worth noting that special cases provides is an effect way to prevent "no-clue questions". – GNUSupporter 8964民主女神 地下教會 Apr 30 '19 at 15:42
• The real missing context is the source and motivation of the problem. – Carl Mummert Apr 30 '19 at 18:50
• CRUDE: "What is the source of FLT?" Fermat: "myself" CRUDE: "What is the motivation of FLT?" Fermat: "for fun" – GNUSupporter 8964民主女神 地下教會 May 1 '19 at 0:14
• @GNUSupporter8964民主女神地下教會 If you actually believe that this is the way that Fermat conceptualized his work, then I would suggest that you have a deeply flawed view of history. While the culture of mathematics was quite different in Fermat's time (e.g. methods were generally regarded as secrets), I am quite certain that he was more than capable of describing motivation for his work and the context into which it fit. Your caricature of Fermat does a disservice to your argument. – Xander Henderson Mod May 2 '19 at 13:36
• Q: Where's the proof of FLT? Fermat: I don't have enough space to write it. Do we have as much sense of humor as the French three centuries ago? – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 15:00
• @GNU sorry to be blunt, but that just does not add up at all. So much so that there just is no joke there even. For a start, the problem is not due to Fermat. The famous margin is that of a published book he was reading (Arithmetica by Diophantus, IIRC) that presented the problem. I am to lazy to check what exactly it is but it's a certainty that there was some context there. For example, that for $n=2$ there is an infinitude of solutions that can be parametrized. Second, and crucially, Fermat never published or even mentioned that 'note to self' (likely as he realized it was wrong). – quid Mod May 2 '19 at 18:11
• @quid Thanks for your math history lesson, but I supposed that's a classic joke whose truth value wouldn't be judged as on the main site. Looking back, that doesn't suit serious math historians. Another meta post might be needed to avoid extended discussion here. – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 19:06
• @GNU what exactly should have been funny? You tried to ridicule others. – quid Mod May 2 '19 at 20:17
• @quid Your question concerns a subjective feeling, so the response is personal, and clearly mine can't be carried to serious math historians, but the historic truth itself is not the main point. If you wish a more serious example, you may consider Ramanujan instead. – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 21:05
• @GNU well, whatever, it seems you did try ridicule others. You tried to make a joke at their expense. This is has little to do with subjective feelings. It's an observation. If your intent was a different one, then what was it exactly? Example of what? Do you want to present Ramanujan as a good example of mathematical communication? What the example maybe shows is that just because something is presented intransperently one should not dismiss it out of hand. However, it seems to me that Hardy and maybe others did try to get Ramnujan to be more transparent. So what again is your point? – quid Mod May 2 '19 at 21:23
• @quid My "joke" is an response to Carl Mummert's comment. It's actually much more simpler than you think. Good math questions can come without source and motivation (comprehensible to others). If asked for a "motivation" and "source" for one of Ramanujan's identities (perhaps by Carl Mummert), what would Ramanujan respond? – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 21:36
• @GNU it's a bit amusing that to prove your point you linked to a question that specifically asks for motivation. Apparently that question for motivation was deemed as a quite meaningful one. First, it's not clear to me what question Ramanujan would have asked. Once you clarify that we might discuss the point. Generally, it's not even clear what your point is. What one might deduce is that "because something is presented intransperently one should not dismiss it out of hand." It's still poorly presented. And, incidentally Ramanujan had to get lucky for somebody even considering it at all. – quid Mod May 2 '19 at 21:45
• Quoting from Ramanujan's wiki page: "An equation for me has no meaning," he once said, "unless it expresses a thought of God." From this, a sensible response for Ramanujan would be an appeal to his own religious beliefs. From your comment to one of my recent meta answer, he wouldn't need to post the religious motivation on the main site. – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 21:45
• @quid I was typing on mobile, and my question "what would Ramanujan respond?" is intended to be answered in the reponse that follows. Many main site questions ask for proofs for an equation/inequality. Which particular identity is not important. Anyone will do, say, Ramanujan's triple product identity. According to Carl Mummert, in order to qualify as a good question, Ramanujan would have to provide a "source" and a "motivation" of his own identity. As a result, he would have appealed to his God, but that's not what the community wanted. So a request for motivation can get sth illogical. – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 22:14

Undeleted, Merged and then deleted

Please reopen https://math.stackexchange.com/q/3208119/290189 since OP has self-deleted his/her own post after getting an answer. The community should have been given enough time to vote.

• You can't reopen a question that isn't closed, GNU. Now it has been closed, as a duplicate, but I don't see how $x^y+y^x=(xy)^2-19$ is a duplicate of $x^y-y^x=xy^2-19$. So, I'm flagging for moderator attention. – Gerry Myerson Apr 30 '19 at 13:47
• @GerryMyerson By the moment I posted this answer, I did voted to close this question as missing context. I did notice the difference between the two. Thanks for reminding me. – GNUSupporter 8964民主女神 地下教會 Apr 30 '19 at 13:52
• @GerryMyerson a problem is that the original version of the question was incorrect. A third party edited it to this version, while main OP had re-asked a different version. – quid Mod Apr 30 '19 at 15:32
• I deleted it after the merge now. This did not work out ideally, but it's near impossible to fix. If somebody wants that version of the question on the site I recommend to ask it anew. – quid Mod May 2 '19 at 18:17

Deleted by a moderator

This question was closed and deleted with the reason given "This question is missing context or other detail". However the author of the question explained both his educational background (he is an undergraduate) and his motivation for the question (it was information that wasn't covered in his degree).

This information is sufficient context to give an answer, indeed I can't think of any further context that a person asking the question could add that would result in a better answer.

• The body does not even contain the question. That question-post is poor, and the thread of very limited value overall. The answers being pretty terse and not giving enough detail. // Added: Given the comment below I'll add that it was not I that deleted it. – quid Mod May 9 '19 at 6:59
• As far as I can tell, if a post was deleted by a moderator - like in this case - the deletion cannot be reversed by regular users. (Of course, voting your posts still can show to which extent users support undeletion - and if there is some support, perhaps moderators might have a look at the the question again.) – Martin Sleziak May 9 '19 at 6:59
• @quid can you explain what is poor about the question? Broadly speaking pen and paper methods of factoring numbers is a subject that the site should have coverage of. – Q the Platypus May 9 '19 at 23:32
• I already mentioned one shortcoming. Further and more drastically, the question does not contain any relevant thought of the OP or even just explanation what they want that information for. For example, do they realize that one can easily recognize that some number are not prime? How would they approach the problem for two digit numbers? Or something else, would all make the question better. That said, the question would arguably be saveable. But what for? The answers are low quality. I'd prefer somebody, say my students, won't find any information here rather than those answers. – quid Mod May 10 '19 at 9:55
• Fortunately similar information is available in other and better threads. In my opinion, the site is quite simply better without this thread. – quid Mod May 10 '19 at 9:57

Closed, deleted, undeleted, deleted, undeleted, deleted, undeleted, deleted, undeleted, reopened.

Unfortunately, the question I asked Why is the zero polynomial the only one to have infinite roots? was put on hold as off-topic first, then closed, and then deleted. I edited it much for it to be reopened, but it wasn't reopened. I apologise if it was off- topic to you, but I edited it. If it being off topic yet, kindly suggest improvement or undelete it please.

Note (quid): I reopened this now. The mass-editing and double posting OP is gone, the question is simple and a bit confused, but arguably not overly contrived and understandable, and answered. It's not impossible somebody else might find this useful at some point. Let's move on.

• Have you finally made up your mind between "Wikipedia" and "wikipedia"? – Did Feb 3 '19 at 21:37

Reopened, closed

Please consider reopening (also for the sake of avoiding further unreasonable strong action of deletion, there has been a delete vote already): How to show for $$x\in \mathbb{R}$$, $$|x|\leqslant 1+x^2$$

This is completely a legitimate question to ask for a beginner. Also, OP did show his/her work in the post, although he/she did not notice what he/she proved is actually a stronger result. Furthermore, it has very well written answers.

I feel it very harsh to close/delete such posts.

• I'd agree with Jack's assessment that the OP already has $2|x|\le1+x^2$ and they missed that this implies the result - and this should count towards context. It would be nice if the OP included how they got $2|x|\le1+x^2$, even if only as a link to some place where this is proved - but since the OP hasn't been seen for a long time, it is unlikely that they add this to the post now. – Martin Sleziak Aug 29 '19 at 7:14
• I'm a bit hesitant to call this "legitimate question to ask for a beginner". It seems to me that noticing that $|x|\leq 2|x|$ and knowing that order is (by definition) transitive is more basic than proving $2|x|\leq 1+x^2$, so I would interpret the question more as the OP having been just momentarily distracted. I doubt it's really necessary to keep that question and its answers. – Arnaud D. Aug 29 '19 at 10:39

Undeleted, reopened

Please consider undeleting this old post: Show that a function $$f:P(X)\to P(X)$$ preserving the subset relation has a fixed point

It was created on Sep 17 '16, has two good answers.

• It seems to be a special case of this question, and Aloizio's anwer in fact answers the general question. So if the goal is to preserve answers, the logical thing to do would be to move them there. – Arnaud D. Jun 28 '19 at 13:48
• It seems to me the Question at issue here has the more general formulation (it does not require an "increasing" function). In any case I've voted to reopen as the Question at issue meets my threshold for context (and it otherwise also on-topic). – hardmath Jun 30 '19 at 19:45
• I disagree with your assertion that the question has two good answers. It has one good answer, and a hint. The question itself is not good at all. I am content to see the question left undeleted, but I see no reason to reopen it. Arnaud D.'s suggestion is, I think, preferable. – Xander Henderson Mod Jun 30 '19 at 23:51
• "I am content to see the question left undeleted." Well, that is what my proposal is. I agree that the question itself was not good enough and thus I did not ask for reopening. @Martin Sleziak has added useful information to the post. (Thanks!) Also, Aloizio's good answer mentions at the beginning "the nice answer by @Brian". – user9464 Jul 1 '19 at 1:47

Undeleted, deleted, undeleted, reopened, put on hold, deleted, undeleted again (the war goes on)

The topic starter solved this problem by using "differentiation or Lagrange multipliers", but he looked for a short solution and he got it.

Thank you!

Undeleted, deleted, undeleted, reopened

Please consider undeleting this post: What is the formula of this angle?

There is a well written and well-received answer to this interesting question.

Undeleted, Reopened

Please consider undeleting and reopening this post: Convergence or diverge of the series $$\sum_{n=1}^\infty\left(\frac{1}{n} - e^{-n^2}\right)$$

OP clearly indicated his/her thoughts at the beginning of the post, and there is a well written (with 10 upvotes) answer.

Undeleted, reopened, closed

What is the maximal number of subsets of a finite set, such that no one is the unions of some other ones? is a serious mathematical question which has attracted two useful answers (full disclosure – one of those two answers is mine). Please have a look and consider casting the third vote to undelete.