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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:

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    $\begingroup$ I edited the post inspired by a concern expressed in a comment. $\endgroup$ – quid Jul 19 at 23:49

173 Answers 173

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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.

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  • $\begingroup$ 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. $\endgroup$ – Xander Henderson Aug 19 '19 at 17:38
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    $\begingroup$ At most "similar" or "related". Not a duplicate. $\endgroup$ – Jack Aug 19 '19 at 17:54
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    $\begingroup$ 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? $\endgroup$ – Xander Henderson Aug 19 '19 at 18:32
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    $\begingroup$ 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. $\endgroup$ – Jack Aug 19 '19 at 18:34
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    $\begingroup$ 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. :-) $\endgroup$ – quid Aug 19 '19 at 18:54
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    $\begingroup$ @quid Indeed, I had missed that. That said, as you note, the distinction is not fundamental. Thank you for handling it. $\endgroup$ – Xander Henderson Aug 19 '19 at 19:39
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Undeleted, reopened, closed-as-duplicate

Please consider undeleting and reopening the edited post: How can one show that $\sum_{n=0}^\infty\frac{n}{n!}=e$?

The user had difficulties in articulating his/her own thoughts. The elementary question in the post is clear. It is also clear from OP's comment and picture attached to the original post what the asker was thinking.

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    $\begingroup$ You should disclose the fact that you made significant edits to the question after it was deleted. The question itself is a duplicate of this question (and probably has other, better dupe targets; I just happen to know the one I linked to since I interacted with it two years ago). I don't see a reason to undelete it. $\endgroup$ – Xander Henderson Aug 28 '19 at 12:31
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    $\begingroup$ I posted a link to an exact duplicate under that thread. Pointless to reopen I think. $\endgroup$ – Jyrki Lahtonen Aug 28 '19 at 18:59
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Reopened


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.

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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.

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    $\begingroup$ Please include a link to the question. $\endgroup$ – quid Feb 3 '19 at 14:54
  • $\begingroup$ its humble request $\endgroup$ – user629353 Feb 3 '19 at 14:56
  • $\begingroup$ why you deleted that $\endgroup$ – user629353 Feb 3 '19 at 14:58
  • $\begingroup$ @quid couldn't you suggest edits $\endgroup$ – user629353 Feb 3 '19 at 15:03
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    $\begingroup$ "couldn't you suggest edits " What do you mean? How am I supposed to know which question you mean? $\endgroup$ – quid Feb 3 '19 at 15:05
  • $\begingroup$ @quid the link of which i have given above $\endgroup$ – user629353 Feb 3 '19 at 15:09
  • $\begingroup$ I misunderstood what you meant. I did not delete you question. At the moment I do not plan to get involved. $\endgroup$ – quid Feb 3 '19 at 15:46
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    $\begingroup$ Two posts here about the same question. Are we supposed to expect some more any time soon? $\endgroup$ – Did Feb 3 '19 at 21:39
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    $\begingroup$ @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. $\endgroup$ – Gerry Myerson Feb 3 '19 at 21:52
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    $\begingroup$ I have flagged the question on main to ask the moderators to let the community make the decision. $\endgroup$ – Gerry Myerson Feb 5 '19 at 11:48
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    $\begingroup$ 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. $\endgroup$ – timtfj Feb 5 '19 at 16:05
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Undeleted, closed, deleted, undeleted, deleted

I think there's a consensus that we undelete questions when they are deleted by the user who posted them after someone else has posted an answer (see, for example, the comment here. In accordance with that consensus, I propose undeletion of this post:

Solutions to $\sum_{j=0}^k r_j^2+3r_j+2\equiv 0 \mod p $

Now I'll own up that I'm the one who posted the answer to the question. My answer was exceedingly terse, and came out of a review with the note, "This does not provide an answer to the question (and so on, and so forth)." But it does provide an answer. The question was to prove or disprove that there are no solutions to a certain equation (congruence, actually, but never mind), and my answer gave a solution.

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    $\begingroup$ Is this actually a consensus? $\endgroup$ – Did Jul 23 '18 at 12:30
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    $\begingroup$ @Did, if you look at the previous edition of this thread, you'll find that in April-May, GNU Supporter posted 4 requests for undeletion, all on the grounds that OP had deleted a question after receiving an answer, and all four questions were undeleted. $\endgroup$ – Gerry Myerson Jul 23 '18 at 12:51
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    $\begingroup$ Yes, and? $ $ $ $ $\endgroup$ – Did Jul 23 '18 at 18:11
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    $\begingroup$ @Did For what it's worth, I have the same impression about the consensus. Preventing an asker from covering up their own question seems to be something the community values, even if it's closed later. $\endgroup$ – user296602 Jul 23 '18 at 18:35
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    $\begingroup$ @T.Bongers (and also Gerry Myerson): I think that there is a moderate consensus that it is bad form to ask a question, get an answer, then delete the question. It belies an ignorance of the functioning of the site (i.e. questions are supposed to be helpful to everyone, not just the one person asking the question). However, in this particular case, the question is of pretty low quality, and should be closed and deleted (in my opinion). It seems like a waste of resources to have opened it back up again... $\endgroup$ – Xander Henderson Jul 23 '18 at 19:00
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    $\begingroup$ For what it's worth, I have expanded my answer to the question on main. $\endgroup$ – Gerry Myerson Jul 24 '18 at 0:34
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    $\begingroup$ "For what it's worth, I have expanded my answer to the question on main." On this topic, my understanding is that the consensus is that a good (or even great) answer is not really enough to justify keeping a poor question around. This and this are relevant. $\endgroup$ – Xander Henderson Jul 24 '18 at 13:27
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    $\begingroup$ @Xander, the highest-voted answers and comments on your first link hardly support your understanding. The second link, even there there is considerable support for not deleting questions with good answers. I'm not convinced there is, was, or ever will be a consensus on this issue. A majority, maybe, but no consensus. $\endgroup$ – Gerry Myerson Jul 24 '18 at 21:31
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    $\begingroup$ @GerryMyerson I think you and I must be reading very different answers. In answer to the question of whether bad questions with good answers should be preserved, my reading of the top three answers ((1), (2), (3)) suggest that it might be worth protecting a poor question if it hosts an excellent answer. $\endgroup$ – Xander Henderson Jul 24 '18 at 22:54
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    $\begingroup$ On the question of upvoting poor questions with good answers, the top voted answer is this one, essentially "I don't do it, but there could be an argument in favor of it." The second answer is similar, with the idea being that a good answer should be preserved if it might be helpful for others in the future. $\endgroup$ – Xander Henderson Jul 24 '18 at 22:55
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    $\begingroup$ In both cases, it seems clear to me that the consensus is that it might be reasonable to preserve a poor question if it attracted a really good, useful, generally helpful answer. Again, a good answer (or possibly even a great answer) is not, by itself, enough to preserve a poor question. $\endgroup$ – Xander Henderson Jul 24 '18 at 22:58
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    $\begingroup$ Finally, I note that I made my initial comment in response to your assertion that you have improved your answer. Are you further asserting that the improvements created something that is of such lasting value that it will be beneficial beyond asking that poor question? Despite the fact that this question and answer have been the topic of discussion here for a couple of days, your answer has not attracted any upvotes... $\endgroup$ – Xander Henderson Jul 24 '18 at 22:59
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    $\begingroup$ @Xander, I'm not in it for the upvotes. I objected to a user posting a question and then deleting it when it got an answer, as I agree with a moderator that such an action is an abuse of the site. Once the question was undeleted, I took the opportunity to improve my answer, in response to a comment from another user. What's wrong with that? I'm not asserting anything about the lasting value of the question or the answer, other than the answer being fuller now than it was. The answer may help someone coming along who is interested in sums of two squares modulo a prime. Fire away. $\endgroup$ – Gerry Myerson Jul 24 '18 at 23:30
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    $\begingroup$ @GerryMyerson: it isn't pleasant to see one's own answer deleted, but in this case the question is clearly not up to many users' standards, so I think it is not surprising to see it deleted. At this point, the question is no longer deleted by the OP, but by several other users. $\endgroup$ – Carl Mummert Aug 5 '18 at 21:06
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    $\begingroup$ @Carl, it isn't pleasant to see any answer with nonzero mathematical content deleted. More to the point, I would not have put the question up for undeletion, had it been deleted by votes of users. My objection was to OP abusing the site by deleting the question after getting an answer. I thought that was clear. $\endgroup$ – Gerry Myerson Aug 5 '18 at 23:09
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Reopened

Could we please reopen: How might I define a parabola in vertex form, such that…

The OP has made an effort to improve their question. They have clarified the question by including the vertex form of a parabola for future reference, and have also added MathJax to the question. I have also cleaned up the tags to better reflect the question ('linear-algebra' was not appropriate).

The question is perfectly clear, and the OP has given the background to their own question which makes it perfectly answerable.

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    $\begingroup$ I have voted to reopen, but I note that the question already has an accepted answer. $\endgroup$ – Gerry Myerson Oct 12 '19 at 6:47
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Undeleted, Reopened, Reclosed as a duplicate.

I found this question sufficiently non-trivial.

Given that the series of positive numbers $\sum_n a_n$ converges, can we say anything about the convergence of $\sum_n a_n^{(n-1)/n}$?

So, as a salvage effort I added some preliminary thoughts to it. Do check whether it now is good enough to be undeleted and/or reopened?

I'm not saying it would now be a great question. This is also a way of repeating my old maxim that the interested parties should always try and edit closed/deleted questions they find interesting into shape, and only after that ask others to reconsider.

Caveat: I didn't feel the need to check for duplicates. So it is possible that it should later be closed and redeleted as a dupe. Not entirely unexpectedly Martin Sleziak found no less than three near duplicates: 1, 2 and 3.

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  • $\begingroup$ I'm happy with the current status (closed as a duplicate). $\endgroup$ – Jyrki Lahtonen Oct 28 '19 at 6:34
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Undeleted

The following answer was deleted:

https://math.stackexchange.com/a/1409573/10513

and I believe it should be undeleted.

The question is rather old (2013). The context of the question is that they are reading a research article which states a result, and the question is asking for a proof of this. Each of the other answers gives a citation rather than a proof. This specific answer is the same (citation, no proof), but the citation given is a modern, standard text and it makes sense for this book to be mentioned in some answer.

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Undeleted

Please consider undeleting this question.

It is a nice instructive problem about a topic that deserves to be much better known and often proves troubling for students - namely Kronecker's ideas relating the factorization of polynomials to the factorization of their values.

Because these ideas are so little known I can understand why the author had trouble getting started (not to mention a red herring assumption added about the polynomial degree). It's such a nice problem that I even added an answer a year later when I stumbled upon it in order to explain how it relates to the general ideas, hoping that I could link to it when similar problems are posted. Alas, that is not possible given the deletion.

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Reopened

Please consider voting to reopen this question:

Peak response of second order system with rectangular pulse input

The OP has improved it a lot.

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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

(1) Uniqueness of a holomorphic function with certain boundary values on an arc

(2) $f$ is bounded, holomorphic in the unit disc, and converges to 0 uniformly in a sector then $f$ is $0$

(3) stein and shakarchi complex analysis exercise 3.15 (b)

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  • $\begingroup$ Is this the exercise from the book, or what is the exercise in the book? $\endgroup$ – quid Apr 5 at 21:58
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    $\begingroup$ The exercise asks the same problem but with additional condition of the function being continuous upto the boundary of the disk. $\endgroup$ – r9m Apr 5 at 21:59
  • $\begingroup$ 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.) $\endgroup$ – quid Apr 5 at 22:03
  • $\begingroup$ @quid If the post is undeleted can I put a link of this post in the question? $\endgroup$ – r9m Apr 5 at 22:25
  • $\begingroup$ 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.) $\endgroup$ – quid Apr 5 at 22:31
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    $\begingroup$ Now undeleted. Please edit as indicated previously. $\endgroup$ – Gerry Myerson Apr 5 at 22:49
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    $\begingroup$ Voted to reopen still need a vote to reopen the topic. $\endgroup$ – Aryadeva Apr 5 at 23:26
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Reopened

Please reopen In chapter 7 exercise 23 of baby Rudin (3rd edition), where does the given recurrence of polynomials come from?.

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.

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    $\begingroup$ 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. $\endgroup$ – Three Sided Coin Apr 17 at 15:13
  • $\begingroup$ @Zacky Thanks for editing the question. $\endgroup$ – Calum Gilhooley Apr 17 at 15:53
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Reopened

Please reopen

The question is clear and natural to ask. It asks whether the characteristic polynomial of a matrix is a polynomial or a polynomial function. One common definition makes it look like the latter.

(Note that quantum groups are not groups and trigonometric polynomials are not polynomial in the usual sense).

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    $\begingroup$ It's considered good manners to indicate, when requesting a reopening, that you've provided an answer to the question yourself :) $\endgroup$ – postmortes Apr 21 at 10:20
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    $\begingroup$ @postmortes, thanks for the info, i didn't know it was relevant. $\endgroup$ – Alexey Apr 21 at 12:31
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    $\begingroup$ Generally if there's a benefit to someone personally by having the question-status changed (typically, they'll gain reputation from it) people here like that stated up front :) $\endgroup$ – postmortes Apr 21 at 12:34
  • $\begingroup$ @postmortes, i was ignorant of the personal benefit... I didn't know or forgot that answers to closed questions cannot be upvoted. $\endgroup$ – Alexey Apr 21 at 19:14
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I believe A paper in English? 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.

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  • $\begingroup$ 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. $\endgroup$ – quid Apr 26 at 10:01
  • $\begingroup$ 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. $\endgroup$ – Martin Sleziak Apr 26 at 10:02
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    $\begingroup$ @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, ...). $\endgroup$ – joriki Apr 26 at 10:05
  • $\begingroup$ 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. $\endgroup$ – quid Apr 26 at 10:10
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    $\begingroup$ @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? $\endgroup$ – joriki Apr 26 at 10:12
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    $\begingroup$ @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. $\endgroup$ – joriki Apr 26 at 10:17
  • $\begingroup$ 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. $\endgroup$ – quid Apr 26 at 10:24
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    $\begingroup$ @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. $\endgroup$ – joriki Apr 26 at 10:30
  • $\begingroup$ 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. $\endgroup$ – quid Apr 26 at 10:35
  • $\begingroup$ @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". $\endgroup$ – joriki Apr 26 at 10:39
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    $\begingroup$ @quid: I see. I think that's a bad tradition. Perhaps I'll write a post about that some time. $\endgroup$ – joriki Apr 26 at 11:07
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    $\begingroup$ @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). $\endgroup$ – joriki Apr 26 at 11:17
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    $\begingroup$ @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. $\endgroup$ – joriki Apr 26 at 11:38
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    $\begingroup$ @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. $\endgroup$ – joriki Apr 26 at 11:39
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    $\begingroup$ Since you care about the old days, certainly you still recall "too localized". $\endgroup$ – quid Apr 26 at 11:41
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Reopened

Please consider this question Some Combinatorics and Some Prime Numbers to be reopened. This was posted by me seeking for other solutions rather than mine. I think it's well explained.

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  • $\begingroup$ Please follow the guidelines in posting here. In particular this (quote): 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.) $\endgroup$ – Arctic Char Jul 22 at 9:36
  • $\begingroup$ Okay, thanks! I got it. $\endgroup$ – Shubhrajit Bhattacharya Jul 22 at 9:39
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Undeleted


Please undelete Invariance of the Lagrangian vs invariance of its integral

It was recently autodeleted by Community because its net vote count was reduced to $0$ by a single vote cast in a recent downvote spree targeting me.

I'm still interested in the topic and am looking forward to an answer or two...

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Reopened

Please re-open this question which is put on hold:

Understanding De/Suspension $\Sigma^{-1}(\Sigma{X})\neq X$

It was said that "unclear what you're asking" and people do not know the def of de-suspension.

However, the suspension is introduced earlier in the cited question:

The suspension (topology) and elementary examples

While the desuspension is also quoted/linked to the Wikipedia (withe refs given by Wiki). I also include a new note: "The desuspension is arguably firstly introduced in the cited text mentioned in H. R. Margolis (1983). Spectra and the Steenrod Algebra. North-Holland. p. 454." And the ref cited.

Follow people's comments, I modify to also ask the basic definitions:

Question: How do we define desuspension exactly? (Please see the comments below, people complain about the meanings of desuspension in Wikipedia is useless).

Are we able to have the desuspension acting on the topological space as the suspension does? Or do we only have the desuspension act on the spectra but not the space?

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Reopened

Please consider reopening this. It was closed originally as missing context. The OP provided some context in the comment and I have added a little bit more. Hope it is okay now.

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  • $\begingroup$ Wow, this question was through reopen review queue already four times. It makes me wonder what is the record. $\endgroup$ – Martin Sleziak Sep 1 '18 at 1:04
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    $\begingroup$ I think it just how difficult it is to reopen a post using only the review queue. @MartinSleziak $\endgroup$ – user99914 Sep 1 '18 at 13:00
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    $\begingroup$ This one has 5 and is still closed. $\endgroup$ – user99914 Sep 1 '18 at 13:01
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Reopened

Please consider reopening the question A functional equation of a matrix that is placed On Hold. I have added my attempt at the cracking the problem if the lack of it was the reason for placing it on hold. The question itself is technically perfectly sound.

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    $\begingroup$ You should have just edited your previous answer, and not added another "answer." $\endgroup$ – Joel Reyes Noche Sep 25 '18 at 7:07
  • $\begingroup$ @JoelReyesNoche: What do you mean? "Answer" to my question that I linked to? I did not post an answer to my own question. $\endgroup$ – Hans Sep 25 '18 at 8:18
  • $\begingroup$ No, answer(s) on the present meta page, there should not be two for a single post on main. $\endgroup$ – Did Sep 25 '18 at 9:31
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    $\begingroup$ I have removed the second post, since this one has been edited to indicate the reopening. I've also edited and deleted/undeleted, so whomever downvoted can undo their vote. $\endgroup$ – Asaf Karagila Sep 25 '18 at 9:56
  • $\begingroup$ @AsafKaragila: Oh, sorry. I did not know the first request was posted as I remembered closing the page rather than posting the "answer" as I needed to leave in a hurry earlier. I posted the second request thinking that the first request was not posted. This is the first time I post in the meta question site. $\endgroup$ – Hans Sep 25 '18 at 10:59
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    $\begingroup$ Why this post says "reopened" when the linked question is still on hold at the moment? $\endgroup$ – Martin Sleziak Sep 25 '18 at 12:31
  • $\begingroup$ @Martin, seems to have been a mistake, which I have rectified. $\endgroup$ – Gerry Myerson Sep 25 '18 at 12:37
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    $\begingroup$ The thing that is missing in the current version of the question, more than work, is the source of the problem. Why do we expect it is true in the first place? $\endgroup$ – Carl Mummert Sep 25 '18 at 19:32
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Undeleted

The deleted answer for Show that there does not exist a unique stationary distribution. should be undeleted.

The question is about "existence of unique stationary measure", and the answer is concise and to-the-point.

"$(1,0,0,...,0)$ and $(0,0,...0,1)$ are two invariant distributions so uniqueness fails."

The existing answer shares the same idea with the deleted one, and it has passed a Low Quality Review.

(Edit: comment removed)

The deleted answer attracted an comment from a high-rep user during another Low Quality Review. However, by appealing to his/her tag score for the relevant tags (, , , , , etc) (and the contributing posts) and comparing them with those of the answerer, you'll have a better idea about their contributions to the site in those areas.

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    $\begingroup$ Oddly, the deleted answer was deleted, not through review, but by its owner. $\endgroup$ – Gerry Myerson Oct 12 '18 at 11:51
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    $\begingroup$ You could ping the author on another of his posts, but I generally oppose undeleting a self-deleted post. $\endgroup$ – user296602 Oct 12 '18 at 15:14
  • $\begingroup$ The author has commented on the other answer, so he can be pinged there if necessary. This is an odd situation. $\endgroup$ – Arnaud D. Oct 12 '18 at 17:34
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    $\begingroup$ Thanks for advice. I did ping the author. He can undelete this anytime he wishes. I ponder whether CRUDE is healthy, when some of its active users vote to delete short answers outside their familiar tags regardless of the quality of the answer. This isolated example shows that its malfunctioning in terms of quality control. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Oct 12 '18 at 20:35
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    $\begingroup$ @GNUSupporter8964民主女神地下教會 This isolated example shows nothing about CRUDE, since the delete votes and the associated comment came from the review queue, and the answer was never mentioned in CRUDE. Besides, I'm not sure tag scores are necessarily an indicator of expertise : for example I have a low score in "integration" because I don't really like to compute integrals, but I still know the basics and I think I'm competent to judge the quality of reasonably simple answers on the topic. $\endgroup$ – Arnaud D. Oct 15 '18 at 12:11
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    $\begingroup$ @ArnaudD. I see your points, but let me clarify my stance. 1. To be more precise, I would say that this post shows the influence of CRUDE participation on other posts (not listed on CRUDE). In a review queue, it's possible that one votes to close/delete within a few seconds. Given the amount of posts that they review every day (in/outside CRUDE), this example reminds us the adverse effect of their rare mistakes dispite their high reputation. 2. That's why I've added "contributing posts" inside the brackets. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Oct 15 '18 at 12:47
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    $\begingroup$ If you read the posts instead of the scores, you'll find out the truth: a) there's no probability theory in his/her "probability theory" answers. These are mistagged (elementary) probability questions. b) His/her stochastic calculus tag score comes from a reference request question. By the way, he/she has removed his/her comment. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Oct 15 '18 at 12:52
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Undeleted


I nominate Group algebra&algebra for undeletion so as to give the community enough time to judge this value of its answer, which is deleted due to the question asker's self-deletion.

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Reopened

(This is to break this request post into two)

I would like, if it is possible, remove the labels close-hold for some of next of my recent post Convergence of $\prod_{n=2}^\infty\left(1-\frac{1}{n^2}\right)^{i^n}$, where $i$ is the imaginary unit

I think that the answers are very interesting and very good, and I think that the questions are in the standard of questions of MSE. Any case many thanks.

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Please reopen The characteristic polynomial of $A$ is $x^n$ if and only if $\text{Tr}(A^i)=0$ for all $1\le i \le n$. due to the reasons listed in OP's comment. The first duplicate matches half of the question. The hypothesis of the second duplicate is different from the first one.

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Reopened

Please consider reopening Is there an injective homomorphism from $S_4$ to $GL(2,C)$ because the question asker has shown efforts in solving the problem, and it has a score of 4 with an accepted answer of score 3 from a 25k user.

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    $\begingroup$ Answers should not be used to judge whether a question should be reopened. But in this case, the asker did include sufficient context, so that's irrelevant. $\endgroup$ – user21820 Mar 25 '19 at 9:44
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    $\begingroup$ "Answers should not be used to judge whether a question should be reopened." That's your opinion, @user – it is not a rule, or even a consensus. $\endgroup$ – Gerry Myerson Mar 25 '19 at 11:51
  • $\begingroup$ @GerryMyerson: It is your comment that is an opinion; it's not even a consensus. Both this and this clearly demonstrate a consensus that "bad questions beget bad questions" and "closed questions can and should be deleted even if the have good but standard answers; only truly great answers should rather not be deleted". $\endgroup$ – user21820 Mar 25 '19 at 12:37
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    $\begingroup$ @user21820 Thanks for your comment. I'll be aware of that next time. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Mar 25 '19 at 16:39
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    $\begingroup$ @user, your quote refers to deletions, not closure/reopening; what's more, the part that says "only truly great answers should rather not be deleted" plainly contradicts your assertions that "answers should not be used to judge...." $\endgroup$ – Gerry Myerson Mar 25 '19 at 21:51
  • $\begingroup$ @GerryMyerson: Firstly, if a bad question ought to be deleted, then obviously it should not be reopened. Secondly, it would be real silly to assume that everything I say is to be taken completely rigidly with no room for exceptions; from my very first comment I meant that as a rule of thumb answers should not be used to judge... $\endgroup$ – user21820 Mar 26 '19 at 5:43
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    $\begingroup$ @user, I'm not sure how I am to tell which things you write are to be taken completely rigidly, and which allow room for exceptions. Maybe we could work out some signal, so in the future I'll be able to tell. $\endgroup$ – Gerry Myerson Mar 26 '19 at 8:51
  • $\begingroup$ @GerryMyerson: Usually, I try to be precise, using words like "typically" or "almost always" but, you know, that that is very tiring to do in every single statement. How about you just assume that there may be rare exceptions unmentioned unless I use the word "absolutely"? I don't think anyone is 100% precise all the time anyway, so that works for interpreting others' comments too. $\endgroup$ – user21820 Mar 26 '19 at 8:59
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Reopened

Please undelete Generalization of the fundamental theorem of duality since the question asker has deleted his/her own question shortly after receiving an answer. This is an abuse of the system.

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Undeleted and reopened

Please reopen Proving the greatest lower bound. because OP has self-deleted his/her own question after I've answered this question. This inhibits the community from viewing the question.

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Reopened

Please consider reopening the following question:

Maclaurin Series Expansion of $\ln(1+\sin x)$

The details which were included afterwards contradict the reason of closure. Moreover they indicate that the OP has as fundamental erroneous understanding of the concept of a MacLaurin Series - and how to derive them -rather than the unwilligness of showing his own efforts. In my opinion the question should be reopened.

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Reopened

Please reopen Am I have right answer about dual problem? since OP has responded to the comment and used MathJax to type out the math. In the revised version, OP has attempted to construct the dual program of the primal program, so it's OK for reopening.

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Reopened

This question was closed as "unclear what your asking":

Show that the order of an element g is well-defined

The issue and its resolution can be seen in the comments to the thread. A brief summary is: I and others didn't understand the question (possibly others influenced by me), but I understand it now. Its fine in its current form.

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    $\begingroup$ @Brahadeesh How is it closed as a duplicate? I didn't see it when I clicked into the question... $\endgroup$ – YuiTo Cheng May 2 '19 at 8:21
  • $\begingroup$ @YuiToCheng Terribly sorry, I could swear I saw it was closed as a duplicate. I'm reverting my edit. Don't know how that happened. :/ I'll be more careful next time. $\endgroup$ – Brahadeesh May 2 '19 at 8:24
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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.

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    $\begingroup$ Question was not merely closed, but deleted. Now undeleted (but still closed). $\endgroup$ – Gerry Myerson Apr 27 '19 at 0:26
  • $\begingroup$ It's worth noting that special cases provides is an effect way to prevent "no-clue questions". $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Apr 30 '19 at 15:42
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    $\begingroup$ The real missing context is the source and motivation of the problem. $\endgroup$ – Carl Mummert Apr 30 '19 at 18:50
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    $\begingroup$ CRUDE: "What is the source of FLT?" Fermat: "myself" CRUDE: "What is the motivation of FLT?" Fermat: "for fun" $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 1 '19 at 0:14
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    $\begingroup$ @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. $\endgroup$ – Xander Henderson May 2 '19 at 13:36
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    $\begingroup$ 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? $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 15:00
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    $\begingroup$ @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). $\endgroup$ – quid May 2 '19 at 18:11
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    $\begingroup$ @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. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 19:06
  • $\begingroup$ @GNU what exactly should have been funny? You tried to ridicule others. $\endgroup$ – quid May 2 '19 at 20:17
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    $\begingroup$ @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. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 21:05
  • $\begingroup$ @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? $\endgroup$ – quid May 2 '19 at 21:23
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    $\begingroup$ @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? $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 21:36
  • $\begingroup$ @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. $\endgroup$ – quid May 2 '19 at 21:45
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    $\begingroup$ 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. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 21:45
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    $\begingroup$ @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. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 22:14

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