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

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  • Please be polite, and respect the many different viewpoints in our diverse community. Please do not use this thread to engage in debates on site policy or other contentious matters. That should be done in a separate linked thread. The goal is to keep this meta thread free of tension, so that everyone feels comfortable posting here.

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Earlier versions of the thread that served as a model:

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    $\begingroup$ Creating a new thread is unnecessary and bad idea, e.g. see here and its links $\endgroup$ Commented Jan 6, 2022 at 10:42
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    $\begingroup$ I applaud annual lists, lest the lists of "answers" becomes difficult to navigate. Also, @Paramanand, thanks for including the links to other "volumes", previously! $\endgroup$
    – amWhy
    Commented Jan 6, 2022 at 20:31
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    $\begingroup$ I'm sorry to be nitpicky about this, but the second bullet point may need some further tweaking. Rather than saying, "Notice that the first edit after the question may push the question into the reopen review queue if the edit is done within 5 days of closure...", it might be better to just say "Any question with significant edits that address the close reason(s) are automatically put into a review queue to be considered for reopening", which is the text in the corresponding Help Center article. $\endgroup$ Commented Jan 22, 2022 at 9:57
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    $\begingroup$ @BillDubuque My answer here that you said should not be deleted, was just deleted. math.meta.stackexchange.com/questions/34447/… $\endgroup$
    – Nick Alger
    Commented Jun 20, 2022 at 22:41
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    $\begingroup$ @Nick Flag it for moderator attention. $\endgroup$ Commented Jun 21, 2022 at 2:01
  • $\begingroup$ @Bill, the answer on meta has now been deleted and locked by "Community" so it can no longer be flagged. $\endgroup$ Commented Jun 26, 2022 at 0:16
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    $\begingroup$ @Gerry the deleted answer is still flaggable for me. In any case one can raise the flag anywhere (e.g. on this question), and Nick has already done so (cf. Math Mods' Office chat). $\endgroup$ Commented Jun 26, 2022 at 3:11
  • $\begingroup$ Why is one user allowed to dominate this thread? If you look at the posts, and the requester who always gets their way, often after inappropriate edits to a poor question, there's a definite pattern of dominance. And I say this only because mods have not yet intervened. I'm surprised that the moderators keep turning their heads in silence and inaction, hence, giving free rein to one user. $\endgroup$
    – amWhy
    Commented Nov 10, 2022 at 21:14
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    $\begingroup$ @amW, anyone is allowed to post to this thread, and anyone is allowed to register disagreement with a requester. If other users disagreed with any one requester's posts, they could vote that user down, with no need for moderator intervention. And if other users haven't complained about one particular user, then I'd say the moderators are quite right not to intervene. $\endgroup$ Commented Nov 11, 2022 at 5:35
  • $\begingroup$ @GerryMyerson Not practically. You play a huge role in that. $\endgroup$
    – amWhy
    Commented Nov 18, 2022 at 20:41
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    $\begingroup$ Not exactly a welcoming interaction here. Unbelievable. math.stackexchange.com/questions/4616434/… $\endgroup$
    – Alper
    Commented Jan 14, 2023 at 18:14
  • $\begingroup$ @Alper I just cast the last needed undelete vote to that posting, so now the posting has been undeleted. However, just so you know, the posting is still closed. I also cast a re-open vote for the posting. $\endgroup$ Commented Mar 4, 2023 at 23:43
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    $\begingroup$ @user2661923 that post was redeleted a couple of weeks ago. $\endgroup$ Commented Mar 28, 2023 at 2:41

83 Answers 83

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Reopened

How do you find the center of a cake with just a knife? was closed as a duplicate of Determine the centre of a circle but it is not a duplicate. Cutting a cake with a knife is not the same thing as drawing lines with an unmarked straightedge; there are things you can do with the one that you can't do with the other. This was not made clear in the original posting of the problem, but it has been made abundantly clear with an edit. Please consider voting to reopen.

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    $\begingroup$ @amWhy, I will stand by my statement that you can do things with a knife and a cake that you can't do with an unmarked straightedge and a circle (and I'm not referring to eating). Did you look at the edit to the question? Did you understand the diagram there? $\endgroup$ Commented Mar 13, 2022 at 23:07
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    $\begingroup$ This is not small stuff, it's not splitting hairs, and it's not being contrarian. You can't find the center of a circle using just an unmarked straightedge, but you can find the center of a circular cake using just a knife. If you don't see how to do it, @amWhy, just take my word for it, it can be done. $\endgroup$ Commented Mar 13, 2022 at 23:29
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Undeleted

Please vote for undeleting this question: Bounds involving number of invariant factors and elementary divisors. The question is interesting, and I provided the OP enough hints in order to solve it, so they could post an answer, or maybe someone else. This way other students will benefit from it.

Last but not least, it was the asker that deleted their question, after helpful comments.

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Reopened

Please consider reopening least time to cross water swimming and running. Someone asked in a comment if it was a duplicate of this question, and I responded no — that question asks how to solve a textbook problem, while mine asks how to generalize that textbook problem. There were no further comments, yet my question was closed, and when I voted to reopen, it was closed again without further comment. I understand that I am supposed to edit my question in some way, but other than responding to the one comment already made, I really don't understand how I can make clearer that I am not looking for a solution to that textbook problem. It is impossible to ask my question without stating the textbook problem. If someone can indicate what is confusing about my wording that makes it seem like I am asking just for a solution of that textbook problem, I will be happy to edit.

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    $\begingroup$ There's nothing confusing about what you wrote; most users just don't read carefully. $\endgroup$ Commented Nov 17, 2022 at 22:16
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Reopened

Why does $\Psi(n)=H_{n-1}-\gamma$ has been closed as a duplicate of Did I derive a new form of the gamma function?. It is stated in my answer to the latter question that $\psi(n)=-\gamma+H_{n-1}$, but nowhere on that page is this equation proven.

I have written an answer to the question that was closed.

I really don't see how the former question is a duplicate of the latter. I think that "Why does $\Psi(n)=H_{n-1}-\gamma$" should be reopened.

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  • $\begingroup$ Agree that it should be reopened. $\endgroup$
    – Paramanand Singh Mod
    Commented Feb 16, 2022 at 10:36
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Update: Question deleted, answer merged with another question's answers.

Consider undeleting and reopening the question

Growth rate of finite simple groups.

The question was sloppily written, but interesting. It was closed; later it was deleted by the system bot. For the record: I wrote an answer to the question, recording what I found in the literature. I also rewrote the question to make it more precise.

Edit: The original question was closed, due to lack of clarity. My edit aimed to improve clarity was rolled back to the original post, as written by OP.

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    $\begingroup$ Your edit was a complete rewrite, given you added context not provided by the OP. If you feel strongly about asking a better question capturing the question you wish was asked, but was not asked, then post a new question to ask it. That is okay to do; but it is not okay to transform a very poor post into a post that was not asked. Ask it your self, instead, in a new post. $\endgroup$
    – amWhy
    Commented Jan 12, 2022 at 19:03
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    $\begingroup$ @amWhy: The essence of question is the same, the difference is the added background and a better formulation. But if the question does not get reopened, I will ask a new question myself. $\endgroup$ Commented Jan 12, 2022 at 20:15
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    $\begingroup$ The new question is here (for those who are <10k). Not sure why there is an edit war on this post.... $\endgroup$ Commented Jan 24, 2022 at 21:45
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    $\begingroup$ I did not intend to participate, and will not continue to edit this answer. I just wanted to make the update use the correct terminology and be more convenient to look at in the future with links. I apologise for any wrongdoings. For Math.SE users who do not know: Here is a link to meta.SE explaining what a merged question is, and here are the guidelines for context rewrites. $\endgroup$ Commented Feb 1, 2022 at 3:13
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Reopened

Request to reopen my question post "What is the name of the symbol = in English?". It has been closed as a "Needs details or clarity" post. I clarified my question's distinction and submitted to review but not accepted as "Original close reason(s) were not resolved". I cannot understand or grasp the reviews' opinion or idea that they thought what is not clear.

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Undeleted.

Seven line segments, with lengths no greater than 10 inches, and no shorter than 1 inch, are given asks a clear and straightforward mathematical question. It was posted in 2015, and soon attracted several answers with net upvotes. But recently it was closed and deleted for "lacking context".

The argument for requiring context is “by providing a context you help the potential responders to your question give you the best help you need.” This argument is inapplicable to a seven-year-old question that already has several good-quality answers.

One of the stated purposes of the site is to be a permanent repository of mathematical questions and answers. Deletion of old posts with good-quality answers is contrary to that purpose. Deletion of this post makes the site less useful.

I suggest this post be undeleted.

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    $\begingroup$ Thanks for reminding me. $\endgroup$
    – hardmath
    Commented Aug 21, 2022 at 12:10
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Undeleted

This question was posted in 2021 deleted by a moderator which prevents the community to cast votes for undeleting and/or reopening. I request that it is undeleted and reopened. The original complain from some users was that it was a question from the American Mathematical monthly (AMM) in 2021. I think the posting is now old enough to be reconsidered for undeleting. It has an answer in AMM, however, the answers given in MSE are relevant and some even different. To moderators, please considering bringing this posting back to MSE or at least let the community vote on this.

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    $\begingroup$ Alas, by SE design, only diamond moderators can undelete posts deleted by diamond mod's. Btw, some users (not I) get really upset if you make such requests and don't explicitly disclose that you have answered the question (which is - of course - obvious to anyone who views it). Just letting you know to help avoid unwarranted downvotes. $\endgroup$ Commented Mar 30, 2023 at 19:22
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    $\begingroup$ @BillDubuque: Yes it is unfortunate, but that can be reversed too, although it takes a little more. $\endgroup$
    – Mittens
    Commented Mar 30, 2023 at 19:50
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    $\begingroup$ Since this request is directed to moderators and not to the rest of the membership, may I suggest it would be better posted to the moderators chatroom than here? $\endgroup$ Commented Mar 30, 2023 at 21:33
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    $\begingroup$ @GerryMyerson: I understand that only a moderator can undo the deletion. My goal to post this request here first is so that the community know about this situation. I will post to the mods chatroom. Thanks! $\endgroup$
    – Mittens
    Commented Mar 30, 2023 at 22:39
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Undeleted

Would you please undelete this post? Find the limit of the recursive sequence using the associated function The asker deleted it just after receiving an my answer.

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    $\begingroup$ "The asker deleted it just after receiving an answer." Indeed, after receiving your answer. It is customary, when asking for an undeletion, to mention one's own participation in the question. $\endgroup$ Commented Apr 7 at 21:59
  • $\begingroup$ I didn't mention it because that was not the point. $\endgroup$ Commented Apr 8 at 6:12
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    $\begingroup$ Well, thanks for this reply. This "custom" remains unjustified to me, but I shall obey blindly next time. I even edit the present request. $\endgroup$ Commented Apr 8 at 10:46
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    $\begingroup$ It's more than just custom - it's requested in the second-to-last bullet in the main post: "If you are involved in the thread which you post about (e.g., you asked the question or you answered it), please disclose this." The point is to try and give undelete/reopen voters a full picture of what's going on when requests are made here. $\endgroup$
    – KReiser
    Commented Apr 8 at 14:27
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    $\begingroup$ Oh thank you @KReiser, and apologies to you and Gerry! $\endgroup$ Commented Apr 8 at 14:46
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Undeleted, reopened

I asked about the cardinality of the space of functionals on square integrable functions, Cardinality of the space of functionals on $L^2$ functions

I believe the question is a good on-topic question very similar to other questions about the cardinality of spaces of functions but new since it is about the cardinality of a space of functionals.

I believe the question was closed due to an initial error on my part in not including what I meant with $L^2$ functions. I have since clarified that I mean square integrable functions and have provided a link to its definition on wikipedia. A further comment asked $L^2$ functions on what space and I clarified I am interested in the cases $L^2(R^n)$ i.e. functions from $R^n \to R$.

I have tried reopening through editing and the undelete progress before but it somehow failed. (I don't believe I received any further comment explaining whether there was still an issue with the question). I still have the same question again months later and was about to write a similar question again when I remembered having asked this question before. So unfortunately for me etiquette requires I do not re-ask but instead try to get my question reopened.

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Reopened

This question has been closed on the grounds that if one read and understood a definition and some results from a wikipedia page, then one could construct an answer which uses the result proven in the answers to the associated question.

The question itself only involves basic ring theory, and the OP has made clear that they find the terminology in the wiki page and associated answer intimidating and prefer my direct answer.

I feel both answers have their merits, and it is not too hard to see that they essentially do the same thing, once you get past the terminology. However the existence of an answer which uses another another answer, does not make a question a duplicate.

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    $\begingroup$ +1. OP explicitly states in a comment that "I have done only 1 course course in commutative algebra and you expect me to learn Von Neumann (regular) and regular rings. I am sorry these terms had nothing to do with my course. " $\endgroup$
    – user1046533
    Commented Jul 10, 2022 at 20:40
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    $\begingroup$ Such close is in the idea of this very old meta post: Coping with abstract duplicate questions. Nevertheless, Arturo's comment (emphasize mine) has yet to be addressed: "It would require the 'survivor variant' to have answers that address both the general strategy (so as to be useful for future minor variants) and specific application to the question at hand (which shows how the general strategy applies to a specific problem)." $\endgroup$
    – user1046533
    Commented Jul 10, 2022 at 20:44
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    $\begingroup$ The claims in the post above grossly misrepresent the matter. Please read all the comments on the question before voting. In fact tkf's use of ultrafilters is surely more foreign to most comm. algebra beginners than is deriving the trivial needed consequences from the simple definition of von neumman regular rings. I fully support user26857's original dupe closure. That the OP strangely does not want to read a simple one-line elementary definition does not mean that the question is not a dupe. $\endgroup$ Commented Jul 10, 2022 at 21:07
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    $\begingroup$ @BillDubuque Yes I agree the term 'ultrafilter' is as intimidating as 'Von Neumann (regular)'. That is why I only mentioned the terminology incidentally, not as a core part of my answer. I think you should give your solution as an answer, only mentioning the terminology 'Von Neumann (regular)' and the associated question incidentally, and repeating the argument from the associated post so your argument is self contained. I would upvote such an answer and believe that it would have value complimentary to mine. But the fact another answer could be given, is no reason to close the question. $\endgroup$
    – tkf
    Commented Jul 10, 2022 at 21:22
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    $\begingroup$ That answer is already given in the linked dupe. It would be ridiculous to duplicate an answer simply because the OP refuses to read a simple definition - viz. a ring R is v.n. regular if for every element a in R there is an x in R with a = axa (true for fields: let x = 1/a for nonzero a), and this property is clearly preserved in products of fields. That's all that one needs to know about v.n. regular rings to use the short simple proof in the dupe (which uses only basic comm. algebra and -further - gives simple characterizations of rings having the property studied by the OP). $\endgroup$ Commented Jul 10, 2022 at 21:32
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    $\begingroup$ I will have deleted the "Closed Reopened Closed" from the top of this post because that space is reserved for actions taken after the post is made here, not for the history of the question before the post here. $\endgroup$ Commented Jul 10, 2022 at 23:00
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Reopened

Please consider reopening the following:

Let $K=F_q(T)$ and $L$ be the spiliting field of the polynomial $p(x)=Tx+x^q+T^q x^{q^2}$ over $K$. Find the Galois group $\operatorname{Gal}(L/K)$.

Was a PSQ, but the OP provided quite some context in the comment and also in the answer they later posted.

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  • $\begingroup$ Rather, Arctic Char improved the question, hence Artic's request to open his question. $\endgroup$
    – amWhy
    Commented Nov 10, 2022 at 22:38
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Undeleted, reopened

Please consider undeleting and reopening this post.

I think the OP had provided enough context (reference, definitions, etc.) and they have self-answered the question.

The reopen review is just completed and it didn't go well.

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    $\begingroup$ Looks to me like it has been reopened. $\endgroup$ Commented Apr 12, 2023 at 0:13
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Re-opened

HERE is one. It came to the front page again today.

Over the years, many posts have asked this same question: compute $\displaystyle\int \frac{dx}{1+x^4}$ . They have all been merged into this one.

It should be reopened. It can serve as the target for any future duplicates.

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Re-opened.

Please consider reopening Example of a PID in which $SL_n \neq E_n$. This is a highly nontrivial and natural question of broad interest which certainly should have an answer somewhere on this site. It is not clear to me what additional context anyone thinks is necessary for the question.

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Undeleted

Please vote for undeleting this answer: https://math.stackexchange.com/a/1933337/121097. It is correct, and for some reason that I don't know it was downvoted twice, and this probably determined the answerer to delete it.

You can also upvote it, since it is way simpler than the accepted answer.

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Reopened

I would like to ask for this question to be reopened: Polyhedron with only π/4 dihedral angles. I think there has been plenty context provided; the OP is responsive in comments and has clearly given it a fair shake; the question has been received well (6 votes). At the very least, it would be nice to understand why some think it should be closed. It has already failed to pass the reopen queue once.

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  • $\begingroup$ I found it somewhat difficult to visualize the angles (e.g. how the "bowtie" is an example of what is described) but I put that down to my own poor geometric positioning rather than a lack of explanation. I voted to reopen (and voted the question up). $\endgroup$ Commented Jul 12, 2022 at 9:19
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    $\begingroup$ @SarveshRavichandranIyer its this bowtie with the same vertices as a square (hence a 'square bowtie') $\endgroup$ Commented Jul 12, 2022 at 10:49
  • $\begingroup$ (After breaking my head trying to understand that diagram for about $5$ minutes and then finally getting it) AHA! NOW I SEE IT! This question is just difficult to visualize, really, it's not lacking context or anything. If anything, feel free to add the diagram as a context edit. It cleared everything up for me. (Actually, perhaps I could get it from the older image as well, so this is just a "me" problem). $\endgroup$ Commented Jul 12, 2022 at 11:00
  • $\begingroup$ I did not vote to close the question, but I do not understand how interior angles are defined in the case of non-embedded polyhedra (OP did not respond). For instance, consider the case of a polyhedral Klein bottle in $R^3$.... $\endgroup$ Commented Jul 12, 2022 at 11:35
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    $\begingroup$ I added the image. @MoisheKohan yes, though what you said wasn't phrased as a question, and your implication to not consider such shapes seems obvious. (also, is that from a conversation that is partially removed?) $\endgroup$ Commented Jul 12, 2022 at 11:56
  • $\begingroup$ @CalvinKhor: I do not understand what you are saying. Do you understand the definition of an interior angle for non-embedded polyhedra? An image (whatever it may be) is not a definition. $\endgroup$ Commented Jul 12, 2022 at 14:18
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    $\begingroup$ @MoisheKohan sorry, the image is unrelated to you, but I didn't want to litter the comments section with two comments. I am essentially agreeing with you $\endgroup$ Commented Jul 12, 2022 at 14:25
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Reopened

Please reopen How come area of all discs in $W=\left( 1-\dfrac{\pi}{4} \right) (1-\epsilon) (a-\epsilon)$?. It has been edited suitably, and I am not sure why it was closed in the first place.

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Reopened

Please consider reopening Circle tangent to rotated ellipse and horizontal line. It seems to me that questions like these are one of the ideal purposes of this site: someone has a math question that they need an answer to for some application (not just some homework exercise they want someone to answer for them) but which is beyond their knowledge. It's not clear to me what additional context anyone would want beyond what has already been provided.

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Undeleted

The answer by Damien D to this question about the Besicovitch-Federer theorem on unrectifiable sets should be undeleted. The reason for the deletion was completely bogus, it is listed as "While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes." - a boiler-plate comment that clearly does not apply to a published book reference. The proof of Theorem 18.1 (part 2), which is Besicovitch-Federer theorem, is quite long and involved, and there is no way one can provide "essential parts" of it in an MSE answer.

Remark: It is possible that Mattila's book "Geometry of Sets and Measures in Euclidean Spaces" (from 1999) is not recent enough to OP's taste, but this is for the OP to decide.

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    $\begingroup$ I agree that this should be reopened, but it still should be improved by, for example, saying "...where the entire theorem is proven". "The proof of Theorem 18.1 (part 2)" could also be mentioned. [I'm happy to do these edits, but don't have access to the book so would just be going by your post here.] $\endgroup$
    – user1729
    Commented Oct 24, 2023 at 11:20
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    $\begingroup$ @user1729: I edited the answer. $\endgroup$ Commented Oct 24, 2023 at 12:44
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    $\begingroup$ I can believe the proof occupies most of its chapter, but surely the statement of the cited Theorem (together with essential setup and definitions) is not too much to ask for an Answer on Math.SE. $\endgroup$
    – hardmath
    Commented Oct 24, 2023 at 20:18
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    $\begingroup$ @hardmath: OP knows the statement and the setup and was asking for a reference to a detailed proof. $\endgroup$ Commented Oct 24, 2023 at 21:06
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Re-opened

Proving Wolstenholme's Theorem has been closed as a duplicate of Proof of Wolstenholme's theorem. However, the supposed duplicate asks not for a proof, but what is wrong with their proof.

The mistakes made in the proof seem easy enough to make, and would be instructive to others, in my opinion.

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    $\begingroup$ Perhaps this should be re-titled, e.g. "What's the mistake in my proof of Wolstenholme's Theorem?" $\endgroup$ Commented Apr 2, 2022 at 12:49
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Undeleted

Please vote for undelete the following answer: https://math.stackexchange.com/a/3739092/121097

I have added the relevant information required in the comments.

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Reopened

I posted this question: Optimal path on the surface of cuboid doesn't visit the same face twice. It was a simple one and someone answered it as a comment. I was planning to expand on the comment and post an answer. This would have been useful for my future reference. However, the question was closed. I'd like to appeal this. Just because its a simple question doesn't mean it can't be useful. The reason says "it doesn't have context". But I feel its completely self-contained and additional context is unnecessary. In any case, I have added it in an edit.

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    $\begingroup$ "Just because its a simple question doesn't mean it can't be useful" and just because it's useful (no evidence given for that) doesn't mean it should be open. Reviewers (and commenters in this case) attempted to ask for some kind of information or elicit some effort out of you , likely because they felt the need to do so instead of answer directly. The link provided is good enough ,in my eyes, for context. Note that "structured optimization" (optimal controls having specific properties) is a big deal in research, and this is a toy example. $\endgroup$ Commented Jun 12, 2022 at 23:42
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Update: This Question has been undeleted and reopened.

  1. A newcomer, unschooled in Mathematical English, posts this reasonable and natural Question:

    • Since there is actually exactly one dog, why do we still say that there is "some" (i.e., at least one) dog?

      In general, how do I know when "some" means at least one, and when it means exactly one?

    My Answer explains that even when we know that there's exactly one dog, it is not wrong to state that there is "some" (i.e., at least one) dog, and that, in many contexts (for example, existence proofs), not only is the latter formulation sufficiently precise, it even makes our work easier.

  2. The Question was closed for lacking details/clarity, and subsequently deleted.

    I am requesting undeletion on the grounds that the Question is legitimate, feels so natural that it is likely useful to future readers in the same shoes, and certainly not an incoherent rubbishy piece of site clutter.

    (And while it is short and inherently reflects the fuzziness of the OP's crystallisation process, it clearly encapsulates the OP's points of confusion; expanding it to give the semblance of fuller context would just be pointless verbiage.)

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    $\begingroup$ This seems to be a duplicate of a more general question. "Reasonable" and "natural" are not, in-and-of-themselves, sufficient reasons to retain a question. "Novel" is also required. $\endgroup$
    – Xander Henderson Mod
    Commented Jul 19, 2022 at 20:38
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    $\begingroup$ If it's a duplicate, I'd suggest it should be closed (and deleted) as a duplicate, rather than with the notice "This question needs details or clarity." $\endgroup$ Commented Jul 19, 2022 at 23:00
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    $\begingroup$ "A newcomer, unschooled in mathematical vocabulary and arguments ... " Obviously, this "context" you mentioned is either being ignored or regarded as useless by the second comment above. $\endgroup$
    – user1046533
    Commented Jul 20, 2022 at 1:15
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    $\begingroup$ @XanderHenderson My undelete request's thesis question is regarding the confusion over multiple interpretations of For Some, whereas your linked question is asking about the difference between For All and For Any, so both questions (each is a good FAQ) in fact cleanly complement each other. $\endgroup$
    – ryang
    Commented Jul 20, 2022 at 2:52
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    $\begingroup$ Your misunderstanding was due to the latter's inaccurate title and irrelevant cursory side-mention of For Some, and the former's similar irrelevant cursory side-mention of For All & Any. (Yes, neither author is a particularly good writer, and I've just edited the latter, for clarity.) $\quad$ Also, note that the two post's Answers do not at all cross-address each other's Questions. $\quad$ (ping @GerryMyerson for reference) $\endgroup$
    – ryang
    Commented Jul 20, 2022 at 2:53
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    $\begingroup$ @GerryMyerson I don't disagree, but the question is currently deleted. It seems like a waste of time to undelete it, reopen it, close it as a duplicate, and then delete it again. $\endgroup$
    – Xander Henderson Mod
    Commented Jul 20, 2022 at 2:56
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    $\begingroup$ @ryang I very much appreciate you mathsplaining to me what it is that I misunderstand. However, I see both questions as fundamentally being about what quantifiers mean. Neither is a very good question (in my opinion), but an answer to one could easily be an answer to the other with very little editing. For example, you could make some very small edits to your answer and post it to the older question. The goal of the site is to create a repository of question and answers---lumping together closely related questions improves the overall quality of that respository. $\endgroup$
    – Xander Henderson Mod
    Commented Jul 20, 2022 at 2:58
  • $\begingroup$ There are other related questions: math.stackexchange.com/q/1593297, math.stackexchange.com/q/4207093, math.stackexchange.com/q/4308984. There are probably others. This seems like a good candidate for a nicely written FAQ post. $\endgroup$
    – Xander Henderson Mod
    Commented Jul 20, 2022 at 3:13
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    $\begingroup$ Have looked through all 4 suggested links: the 5 posts collectively are at best cousins. Distilling such Questions into a bigass FAQ is as reasonable/realistic and fair as doing likewise for Questions related to parabolic curves. $\endgroup$
    – ryang
    Commented Jul 20, 2022 at 13:00
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$\begingroup$

Reopened.

Please consider reopening Planar Quartic Curve invariants for number of connex components. This question was originally unclear because it did not explain that it was working over $\mathbb{R}$, but now it has been edited to be clear.

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$\begingroup$

Reopened

Please consider reopening Dodechadron, angle between edge and face.. This is a natural question of broad interest presented with clear motivation. It seems to me that questions like these are one of the ideal purposes of this site: someone has a math question that they need an answer to for some application (not just some homework exercise they want someone to answer for them) but which is beyond their knowledge, and they are unable to find an answer elsewhere on the internet.

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0
3
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Reopened

I would like to request reopening for: Find the minimum of $\sqrt{\cos x+3}+\sqrt{2\sin x+7}$ without derivative

This is a very clearly posed question which the OP has made considerable and clear effort into and has attracted a high quality answer. The close reason seems unusual to me as knowing the source of the question does not change the quality of the post.

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The following two questions were deleted by the Community bot, though neither seems to fit the automatic deletion criteria.

    How do you factorise $x^2+7xy+my^2-5x+43y-24$?
    Factorize $-16x^3+36x^2-24x+5$ without using calculator

On a closer look, they were both posted by an (ex-)user, "destroyed" by the same Community bot.

Don't know whether it is appropriate to list such questions here, and could not find any guidance about that on a quick search. Assuming it is, IMHO the questions did not deserve deletion on their own merits.


[ EDIT ] More upvoted questions with upvoted answers that got "destroyed" alongside the user are listed in google's cache of the profile (while it lasts). I am not saying that any of those is irreplaceably valuable, just that it looks odd to 10k+ users who happen upon them to see an otherwise OK question deleted by the Community bot without an apparent reason. Those who dig into the timeline will be twice confused to see it was done because of "user destroyed", typically reserved for spam or rude/abusive behavior, neither of which applies to those questions.

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  • 2
    $\begingroup$ Some context on "destroyed" is here. $\endgroup$
    – KReiser
    Commented Jun 23, 2023 at 3:40
  • 1
    $\begingroup$ @KReiser Thanks for the link. Some more on the same topic here on a different SE site, which appears to confirm that "destroyed" users get listed as "by Community bot" in the timeline. However, neither of these provides any advice or direction about undeleting "destroyed" questions. $\endgroup$
    – dxiv
    Commented Jun 24, 2023 at 21:06
  • $\begingroup$ @dxiv Undeleting such a question is the same as undeleting any other question. That being said, is there any great value in keeping either of these around? Don't we have enough questions asking about factoring polynomials already? $\endgroup$
    – Xander Henderson Mod
    Commented Jun 26, 2023 at 23:48
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    $\begingroup$ @XanderHenderson I believe what I wrote answers that part ("not saying that any of those is irreplaceably valuable"). But that was not the point. What looks somewhat arbitrary here is punishing an otherwise OK question (alongside with its answers) for unrelated/untold sins of the asker. $\endgroup$
    – dxiv
    Commented Jun 27, 2023 at 1:34
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    $\begingroup$ @dxiv No question is being "punished". This is what happens when an account is destroyed. Note that accounts are rarely destroyed, and that destruction of an account is typically related to a lot of disruptive behaviour. I don't know what happened in this case, (as I am not currently moderating), but it is highly likely that the user earned the destruction of their account. Do you really expect moderators to have to go through everything that a destroyed account has posted in order to find the appropriate material from the inappropriate? $\endgroup$
    – Xander Henderson Mod
    Commented Jun 27, 2023 at 14:05
  • 2
    $\begingroup$ "Do you really expect moderators to have to go through everything that a destroyed account has posted in order to find the appropriate material from the inappropriate?" @Xander, the moderators could delegate that task to trusted users. $\endgroup$ Commented Jun 29, 2023 at 22:46
  • $\begingroup$ @GerryMyerson The deletion of content is automatic, and happens when the user is destroyed. What you are proposing would require some major technical changes to the way the site works. There is nothing that can be done at a Math SE level to change this. If you think that it is worth the effort, I would suggest that you bring this up on the main meta. $\endgroup$
    – Xander Henderson Mod
    Commented Jun 29, 2023 at 22:57
  • 1
    $\begingroup$ @Xander, "Undeleting such a question is the same as undeleting any other question." If I understand that correctly, all it would take is a message from a moderator to a trusted user saying "please have a look at the following list of deleted questions from a destroyed user and report back to me on which ones, if any, you think are appropriate for our website". No technical changes, and nothing that can't be done at the Math SE level. $\endgroup$ Commented Jun 29, 2023 at 23:05
  • 1
    $\begingroup$ @GerryMyerson If you say so. Personally, I have no desire to increasing the complexity of a mostly automatic process in order to save the one-in-a-thousand question which might be of some value. If you can convince another moderator to spend their time in this manner, be my guest. $\endgroup$
    – Xander Henderson Mod
    Commented Jun 29, 2023 at 23:08
  • 1
    $\begingroup$ @GerryMyerson What you propose would make sense, unfortunately I don't expect the idea to fly (as confirmed already). The blanket "destroy" rules in effect are probably justified in the majority of cases of blatant spam or abuse. No less importantly, they are safest and most convenient for the mods. I guess atypical cases like the one here are rare enough that they don't truly care about such collateral damage. FWIW the user in question had been around for several months, and was just under 500 rep, which is the threshold past which they would have been suspended/deleted rather than destroyed. $\endgroup$
    – dxiv
    Commented Jun 30, 2023 at 3:53
3
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Reopened

Request to reopen the following question Proof of the Existence of All Phone Numbers in Pi.

Related meta dicussion: Should this special case question (that has a proof) be marked as a duplicate of the general case question (that doesn't have a proof)?

I recently found this question: Proof of the Existence of All Phone Numbers in Pi

I understand why it can be seen as a duplicate of Does π contain all possible number combinations?, but the question is much more specific and there is a proof that doesn't need π to be a normal number: a proof by exhaustion.

As discussed in my comment, since the early 2000s, we know enough digits of π to prove that it contains all 10-digit number sequences with an exhaustive search. However, this proof wouldn't make sense as an answer to the question on all possible number combinations.

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11
  • $\begingroup$ We even know that all digit strings of length $11$ occur. But what is then the question ? It follows from the known digits of $\pi$. A proof is obsolete. $\endgroup$
    – Peter
    Commented Sep 1, 2023 at 21:15
  • $\begingroup$ Noone knows how this result can be extended to , say , the digit-strings with length $30$. We only know the above result because the digits have been calculated. Noone is able to predict anything here. So no , there is no alternative proof that does not use the awfully many calculated digits. $\endgroup$
    – Peter
    Commented Sep 1, 2023 at 21:18
  • $\begingroup$ But to know that "all digit strings of length 11 occur" we need a computer-assisted proof. It doesn't follow directly from looking at the digits of π with the human eye due to the length of the search. $\endgroup$ Commented Sep 1, 2023 at 22:02
  • $\begingroup$ Anyway , we cannot prove the occurence of a given digit string in $\pi$ , unless we do not already know that it is there ans where. So, the only possibility we have with our current knowledge is to look at the digits , we have nothing better. And of course , we must trust the computer that the digits are correct. So I do not understand the point. $\endgroup$
    – Peter
    Commented Sep 1, 2023 at 22:08
  • $\begingroup$ @Peter I think there are still interesting discussions to have regarding this exhaustive search. For instance, assuming the digits of π are distributed randomly, how many digits are expected to be required to have all the n-digit strings appear at least once? Also, there are interesting methods to verify that the digits are correct such as the BBP algorithm. I would gladly post an answer to the question to expand further on these discussions, but as long as the question is closed, I can't. $\endgroup$ Commented Sep 1, 2023 at 22:25
  • $\begingroup$ If you mean the shortcut to determine the digits without having to calculate all previous digits : For $\pi$ (and only for $\pi$) such a shortcut is actually known , but sadly only in base $2$. And although we do not need the complete binary expansion , we still cannot determine some binary digit immediately , it still takes a lot of time , if it comes "late" in $\pi$. $\endgroup$
    – Peter
    Commented Sep 1, 2023 at 22:31
  • $\begingroup$ @Peter I mentioned the BBP algorithm because your said "And of course , we must trust the computer that the digits are correct". What I meant is that we can use BBP to check that the digits we are using are correct (to almost 100%), we don't have to trust them blindlly. See also: youtube.com/watch?v=nMqdRu9gGGs&t=167s $\endgroup$ Commented Sep 2, 2023 at 2:34
  • $\begingroup$ As said, this algorithm only works in base 2 , so I see no possibility to check digits without computer help. We also cannot "prove" that the largest known prime is prime. We must trust the computer calculations. The situation is the same. $\endgroup$
    – Peter
    Commented Sep 2, 2023 at 7:32
  • $\begingroup$ @Peter 1) The BBP algorithm is used to calculate digits in base 16 (hexadecimal). 2) There are ways to convert a base 16 number to base 10 (and vice versa), so this just adds an additional step to the checking process. $\endgroup$ Commented Sep 2, 2023 at 15:32
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    $\begingroup$ @Peter What do you mean by saying "a proof is obsolete"? Checking the known digits for all 10-digit strings is a proof. And considering that this question was closed as a duplicate of a question regarding the normality of $\pi$, which is unknown, it seems not to be too widely known that enough digits of $\pi$ are known to answer the question for 10-digit strings (at least among the close voters). $\endgroup$
    – MaoWao
    Commented Sep 2, 2023 at 16:21
  • 11
    $\begingroup$ In any case, it seems clear to me that a question whose answer is known cannot be a duplicate to a question whose answer is unknown. We also do not close a question asking if there are infinitely many primes as a duplicate of a question asking if there are infinitely many prime twins just because a positive answer to the second question would imply a positive answer to the first. $\endgroup$
    – MaoWao
    Commented Sep 2, 2023 at 16:23
3
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Undeleted

I am requesting to reopen "Bounding with exponential Markov inequality".

The asker posted a question and showed the work that they had done so far. They explained where they got stuck (can't show $at-\phi(t)$ is positive), and their unsuccessful attempts (Taylor expansion). I explained why they were attempting to prove the wrong thing ($at-\phi(t)$ need not be positive, but rather they should show that $\sup_t (at - \phi(t))$ is positive) and provided a path to show this, along with some context.

The asker deleted their question after I posted my answer. Could the question be reopened? I think my answer could be useful to others.

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    $\begingroup$ By the way, deletion of a question after answers is cause for moderator intervention as well - flagging can help with this sort of thing too. $\endgroup$
    – KReiser
    Commented Sep 10, 2023 at 22:52

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