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Since I expect this may prove rather useful, I'm blatantly purloining Asaf's question from meta.math.se.

Please post general requests for reopen votes as answers below.

Beware that "short" requests such as "request reopening of <link>" may be automatically converted to comments by the SE software, so you will need to say more, such as why you think that the question should be reopened.

Please do not use this thread to engage in debates on contentious matters (e.g. reasons for closure). That should be done in a separate thread - which can be linked to from here.

If a question is reopened then please put [REOPENED] at the start of the request (answer).

Of course, each requested question may need some editing or other improvements before it is fit, and as indicated elsewhere, this is desirable, and I hope may be expedited through this thread.

(Improvements on the phrasing are welcome.)

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    $\begingroup$ Not entirely necessary. There's a reopen queue now. A closed post can be put into the reopen queue by editing or voting to reopen. 3k+ users can vote to reopen (or alternatively vote against it). If this mechanism fails, then one can open a separate meta post about the question. I find that this is a more efficient process :) $\endgroup$ Commented Jun 27, 2013 at 21:10
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    $\begingroup$ @Manishearth: Not everyone has access to the queue history, so not everyone can tell when a thread has been "outlived its review" and it is time to come to meta. In the long run, I think it's better to have one post for "run of the mill reopen votes" rather than having more and more separated questions whose answers would consist mostly of "Done." $\endgroup$
    – Asaf Karagila Mod
    Commented Jun 27, 2013 at 22:06
  • $\begingroup$ @AsafKaragila Yeah, I see your point -- but "outlived its review" can just mean "wait a day", regardless of its queue status. So, if a reopen vote or edit doesn't push it out of the queue in a day, then come to meta (and post on this post, or separately -- IMO separate meta posts lead to better discussion, but that's just me). But if you take a look at the MSE post: Most of the recent ones are either obvious nos (closed post) user whinging about closed post, or obvious yes's (Awesome edit improved post). $\endgroup$ Commented Jun 27, 2013 at 22:31
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    $\begingroup$ These can be dealt with fairly within the review queue itself; giving an explicit platform on meta for people to whinge or where people feel obliged to post obvious reopens is imo unnecessary. Again, I don't know much about MO or MSE, so I could be grossly wrong here :). Just giving an outsider's viewpoint. $\endgroup$ Commented Jun 27, 2013 at 22:32
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    $\begingroup$ I agree with Manishearth: with the new "on-hold" -> edit -> add to re-open review queue mechanism, threads like this should be much less necessary. $\endgroup$ Commented Jun 28, 2013 at 9:21
  • $\begingroup$ @AsafKaragila Btw, this is why doing it separately is imo better, you get a lot more feedback and discussion. $\endgroup$ Commented Jun 28, 2013 at 16:59
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    $\begingroup$ I dont want to interfere here with anything but I disagree with Manishearth about the usefulness of this Request to Reopen List. At Math SE I have observed that it works very well and efficiently to get questions reopend without making much fuzz about it. At Physics SE, we controversely discuss each question that somebody thinks should get reopend at meta seperately at length with the effect that people just discuss instead of just doing it, and almost nothing gets reopend at the end. $\endgroup$
    – Dilaton
    Commented Jul 3, 2013 at 17:44
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    $\begingroup$ Reopening questions the way people at Math SE do, has in my opinion the additional advantage that people who have less than 3000 rep and therefore not yeat access to the Reopen queue can take part in the reopen process by upvoting the answers of this post, which makes reopening of questions that deserve it more efficient. $\endgroup$
    – Dilaton
    Commented Jul 3, 2013 at 17:54

113 Answers 113

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https://mathoverflow.net/questions/379145/geometric-combinatorial-problem-in-the-euclidean-space

This question was deleted by nobody less than @ToddTrimble just 10 days ago after having 9 upvotes and a few answers. The problem is neither ridiculous, nor fully resolved, and I see absolutely nothing out of the ordinary with either the question itself, or any of the answers, so I'm quite curious if it was a deletion by mistake or something sinister is going on here.

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  • $\begingroup$ Probably it is worth reminding that an answer which was deleted by a moderator cannot be undeleted by regular users. (But I suppose you're aware of this - if you tried to cast an undelete vote, you saw a pop-up explaining this.) $\endgroup$ Commented Jan 28, 2021 at 22:36
  • $\begingroup$ Yep, I know that. That's why I also tried to attract the attention of @ToddTrimble to it though I'm not really sure if the at symbol works in the answer body. Any other moderator would do too :-) $\endgroup$
    – fedja
    Commented Jan 29, 2021 at 1:03
  • $\begingroup$ You may want to flag Todd (flag any of his comments anywhere). No idea if this happened here, but it could be it was deleted by mistake. $\endgroup$ Commented Jan 29, 2021 at 1:35
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    $\begingroup$ I have responded here: chat.stackexchange.com/transcript/message/56897449#56897449 I understand why the situation seems confusing, but it was not deleted by mistake, and there was nothing sinister going on. The other moderators can see what happened as well. $\endgroup$
    – Todd Trimble Mod
    Commented Jan 29, 2021 at 16:17
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    $\begingroup$ This reminded me of another question that I was surprised to see deleted by a moderator, despite of several answers with upvotes. I even suspect it might be the same author (I noticed they tend to delete their questions quite a bit). mathoverflow.net/questions/376821 $\endgroup$ Commented Jan 29, 2021 at 19:09
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[REOPENED]

A question Finite groups with no elements of order $p^2q$ originally closed was heavily edited by Yves Cornulier and Nick Gill.

There are three votes to reopen already, but the question is already a bit out of sight, thus this posting.

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[REOPENED]

The question

Finding all local maximum points of a function?

does not seem as trivial to me as has been supposed. Sure, one can set the gradient equal to zero, but how does one actually prove that the only solutions are the "obvious ones"? At the very least it seems worth leaving the question open for a while.

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$\begingroup$

A couple of questions about Turing machines that are bounded in space but have an infinite amount of time in which to operate.

I think some votes to close here were due confusion related to an earlier version of the question where the OP experienced technical difficulties. The objection that the OP's SBTMs are finite state machines is incorrect. Moreover, SBTMs are not completely ad hoc or unmotivated, the computer you are using to read this sentence is essentially an SBTM.

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  • $\begingroup$ The objection that the OP's SBTMs are finite state machines is incorrect. Why? Perhaps we are interpreting the definitions differently? $\endgroup$
    – fedja
    Commented Apr 28, 2019 at 14:39
2
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[REOPENED]

I think this question:Are there infinitely many natural numbers not covered by one of these 7 polynomials? should be reopened. Please see the comments by me and Joel in main.

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    $\begingroup$ I think the question in its current form is actually quite bad, but the additions from the comments by the OP help. Specifically, it asks how he can prove something that he only suspects to be true, rather than asking whether it is true. And with no further details, the question is way too specific (I mean, if I was to ask the same question about the same polynomials except I change one coefficient in one of them, why would that not also be an equally good question?) $\endgroup$ Commented Apr 30, 2014 at 19:24
  • $\begingroup$ @TobiasKildetoft: I think if you change the coefficients it would still be an interesting question, as I mention in my comment. The general question, of which the original one is a special case, is unclear to me. The current question is clearly stated, and the answer is not at all obvious. You may not be interested in the question, which is fine, but note that the question was closed as being not up to research level (without indicating any answer). $\endgroup$
    – Lucia
    Commented Apr 30, 2014 at 19:32
  • $\begingroup$ I agree that the general type of question is of interest. But focusing on a special case is not unless that special case has some additional property, either coming from something else or for some reason being "generic". An answer to this question that would not work for any other set of polynomials at all would for example be completely uninteresting, but answer the question. $\endgroup$ Commented Apr 30, 2014 at 19:38
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    $\begingroup$ @TobiasKildetoft: I think you are wrong here, but of course you are entitled to your opinion. $\endgroup$
    – Lucia
    Commented Apr 30, 2014 at 19:39
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The question How to find generators to Mordell weil groups of elliptic curves? was originally phrased in the narrow context of inquiring just about the software Sage. I had voted to close that, but the revised more general question seems worth reopening. I have cast my vote to reopen, but am not sure that the revised question has received enough attention.

(Also, this meta question now has too many answers, and perhaps it's better to start a new thread with the same intent. When I wrote this reopen request, the system wanted to know if with 30 answers to this question whether I really wanted to add another one.)

[REOPENED]

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    $\begingroup$ I would say that a message popping up when you post an answer is a small price to pay for having everything gathered one place. $\endgroup$ Commented Sep 2, 2014 at 17:59
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[REOPENED]

The question Isomorphism problem for two radical extensions originally had an error in its formulation. This was subsequently corrected by OP, and the question seems quite interesting and has attracted good answers (including one that somehow came in after the question was closed!). I think it should be reopened.

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[REOPENED]

This question If $\binom{2p}{p}$ is $(-1)^{p-1} \bmod 2p+1$ is then $2p+1$ prime? was mistakenly closed (by me, among others). I have cast my vote to reopen. The question has been answered in interesting comments by Robert Israel and YCor.

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[UNDELETED]

The question On isolated points of the approximate point spectrum of a bounded operator looks reasonable and did not attract any negative comments or downvotes. I propose that it should be undeleted.

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[UNDELETED]

The question Generalized arithmetic progressions contained in Bohr sets looks reasonable and did not attract any negative comments or downvotes. I propose that it should be undeleted

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[REOPENED]

Basic Definition and Notations in RWRE is exactly what it says: a question about definitions and notation used in the study of random walk in random environment (RWRE) within probability theory. This is a very active research area, with a rather specific and idiosyncratic vocabulary and notation which can certainly be challenging for newcomers to the topic. These notions are not part of the standard graduate probability curriculum; at best one might see them in an advanced special topics course.

I think this question is certainly research level and should be reopened. I left a comment to that effect which has 4 upvotes. The question itself also has 4 upvotes and 0 downvotes.

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    $\begingroup$ I agree with Nate and have voted to undelete $\endgroup$
    – Yemon Choi
    Commented Jul 11, 2016 at 22:28
2
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[REOPENED]

I would like to request to reopen Relation between the Hochschild cohomology of group algebras and groupoids. The original question was very vague, but it has since been edited and is now, in my opinion, a perfectly fine question.

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[REOPENED]

This question, which started out extremely confused, is now a well defined question asking for a sketch of a proof of a theorem of Serre in differential geometry. Probably not a great question, but it seems like the sort of question we would have accepted if it were asked in this form to begin with, so I've voted to reopen.

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[REOPENED]

Please have a look at the comments at https://mathoverflow.net/questions/135605/how-to-discover-counterexamples-and-required-objects? and consider voting to reopen.

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  • $\begingroup$ On a procedural note: why is this (already) posted here, when the question had already its own meta question? (In addition to being still on the frontpage, even now hours later, so it was presumably fairly to the top when this was posted.) $\endgroup$
    – user9072
    Commented Jul 3, 2013 at 12:55
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    $\begingroup$ @quid, I didn't see that meta question. There was no link to it at the original, and nothing in the name of the meta question to draw my attention to its relevance here. Shall I withdraw this question? $\endgroup$ Commented Jul 3, 2013 at 13:38
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    $\begingroup$ thank you for the reply. I do not think it is necessary to withdraw this post now. My comment was also meant to help form some consensus when one should post here. I take you reply as you agreeing with me that in principle one should rather not do so in parallel with an existing meta-disussion on the question. I agree the meta-question in this case was hard to notice, which I tried to fix now, before even noticing you reply. $\endgroup$
    – user9072
    Commented Jul 3, 2013 at 13:43
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[REOPENED]

This question, on a geometric inequality, was closed due to its poor original wording. After the edit, it appears to be a reasonable problem.

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    $\begingroup$ The question was closed not due to its poor original wording but because the author intentionally concealed information about known results (some published, some not), relevant numerical evidence, etc., apparently in order to issue a "challenge". I think it's great that Andres has edited the question to add this information but as long as the OP has made no effort to cooperate, or acknowledge Andres's efforts, I am reluctant to vote to reopen. $\endgroup$ Commented Jul 15, 2013 at 6:26
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    $\begingroup$ There's of course a good argument for saying that we want good questions wherever they come from. But there's a countervailing good argument for saying that bad behavior will tend to get your question closed. $\endgroup$ Commented Jul 15, 2013 at 6:27
  • $\begingroup$ (I agree with Steven.) $\endgroup$ Commented Jul 15, 2013 at 6:53
  • $\begingroup$ As the question stands now it is a blatant nonsense--the sum of points on a unit circle $\ S,\ $ centered at $\ 0\ $ is not $\ 0,\ $ not in general. Consider $\ n=1.\ $ or any positive $\ n.$ $\endgroup$ Commented Feb 26, 2015 at 4:13
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[REOPENED]

The question

The probability for a streak when tossing a coin

was closed quickly, but as far as I know, this is not an exercise. There is a complicated approximation in Feller's classic text.

As suggested in this question, I put more discussion in a separate thread.

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[REOPENED]

Question on a concrete example of n points has been improved considerably since it was closed and might be considered for re-opening.

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[REOPENED]

The question Proving $\sum_{k=0}^{2m}(-1)^k{\binom{2m}{k}}^3=(-1)^m\binom{2m}{m}\binom{3m}{m}$ was closed as "off-topic." As far as I can tell, it is reasonable, and of interest to many as shown by the answer, upvotes, comments, and favorites. Quite a few mathematicians find this identity interesting, don't know Dixon's Theorem, and would take a while to prove it on their own.

I added a tag and rewrote the request for help to look a little more professional. I don't think that those should be grounds for closing. They are reasons to edit the question or perhaps vote it down, but not to block others from answering the question.

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  • $\begingroup$ Isn't the idea of being "on hold" (rather than "closed") precisely so these changes you suggest are implemented? Once the changes are in place, and things appear reasonable, reopening it is the natural course of action. (This is the same idea behind closing votes being reversible, isn't it?) $\endgroup$ Commented Sep 28, 2013 at 6:17
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    $\begingroup$ You do not need to close a question in order to add a relevant tag, or to make a minor change. Closing this question blocked Mark Wildon from answering it. How does that help? $\endgroup$ Commented Sep 28, 2013 at 6:19
  • $\begingroup$ (The question has been reopened, by the way. The last opening vote was mine.) I agree, but some people feel it should be the OP who carries out these changes. $\endgroup$ Commented Sep 28, 2013 at 6:22
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[REOPENED]

The question Square of primary ideals was originally closed as being "unclear what you're asking", but after the edit I don't think this is a valid reason anymore. (I'm no expert here, but it seems like a reasonable question to me.)

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[reopened]

Edit I edited the question.


I think that the question

How to construct a group with specified growth function

Is not an unreasonable question and I don't fully see why it is closed. The English is not optimal and no motivation is given, but it is not alone in that respect. The basic underlying question is reasonable (note also that the OP, based on previous questions, seems to come from formal language theory, not group theory). The basic question is whether there is some procedure (perhaps algorithmic) to construct groups with a prescribed growth function.

Of course, constructing groups with intermediate growth is a difficult problem and I don't even think there is a procedure in general for semigroups (except one by Bergman for certain growth ranges). Work like http://arxiv.org/abs/1108.0262 is to some extent concerned with variations of this question.

So I think it is reasonable to leave it open even if a complete answer seems out of reach.

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    $\begingroup$ I agree that one could ask a reasonable question about prescribing the growth of groups. However, this is not it. For instance, I don't know what the OP means by "manifold", and I don't know exactly what the OP means with regards to a growth function, e.g. what's the equivalence relation? For instance, as written he might have a specific function and want a group with a specific finite generating set realizing that specific function on the nose. Someone (either you or the OP) should rewrite the question before it is reopened. $\endgroup$ Commented Dec 8, 2013 at 3:13
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[REOPENED]

I asked in a separate thread about the closing of the question a question on 0-1 valued stochastic process, located at a question on 0-1 valued stochastic process, and it was suggested that here would be the good place to bring it up.

The question was closed very speedily - I'm not particularly sure why. It's surely not a very exciting question, and I think it has a fairly straightforward answer, but it seems reasonable for someone to ask. I wouldn't be surprised if a colleague asked me it in the department. Anyway, I don't have strong feelings; but I am surprised that the question was migrated to stats.stackexchange, since as far as I can see, it isn't even on-topic there - that site is supposedly for "statistics, machine learning, data analysis, data mining, and data visualization" (although possibly the usage is broader than that definition).

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  • $\begingroup$ It appears that the migration to stats was rejected. $\endgroup$ Commented Apr 9, 2015 at 0:59
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    $\begingroup$ Actually, the stats mod reported that it would have been on-topic for their site, but also that it might fare better at MO if it were reopened. It is currently on hold at MO and could be reopened with five votes. Incidentally, James, is this a question you'd be prepared to answer? $\endgroup$
    – Todd Trimble Mod
    Commented Apr 9, 2015 at 1:27
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    $\begingroup$ As a stats.SE moderator, I can confirm @Todd's comment regarding this question being on-topic at stats. We'll consider clarifying the scope a little bit on our help pages. Thanks for mentioning it. Cheers. $\endgroup$
    – cardinal
    Commented Apr 9, 2015 at 21:27
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[UNDELETED]

The question

Does there exist some $C$ independent of $n$ and $f$ such that $ \|f''\|_p \geq Cn^2 \| f \|_p$, where $1 \leq p\leq \infty$?

seemed decent enough and had a good answer from Christian Remling, but was deleted by its author. Do we have a standard policy here for self-deleted posts?

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    $\begingroup$ An answer (mathoverflow.net/a/231246) has been reinstated, and Remling claims the previous answer was wrong. $\endgroup$
    – David Roberts Mod
    Commented Feb 17, 2016 at 6:10
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    $\begingroup$ For the record: I am not sure about a standard policy, but excepting unusual circumstances including noticeable spite or vandalism (inapplicable in this case), I can see little reason not to just accept the author's wishes regarding the status of their answer. There is a reason self-deletes do not even show up in the standard list of deleted posts. $\endgroup$
    – user9072
    Commented Feb 17, 2016 at 7:28
  • $\begingroup$ @quid: my issue wasn't with the deletion of the answer, but the deletion of the question $\endgroup$
    – Yemon Choi
    Commented Feb 17, 2016 at 12:47
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    $\begingroup$ Sorry I misunderstood this, in part due to the preceding comment. For deletion of questions, I would say the same, except if it is unmotivated and/or deletes valuable answers in the process. This case is rare as the software is by now very rigid in this regard (this used to be more flexible). A delete of a question with answer is only possible if there is only one answer and this answer has no upvote (note it really no upvote, not positive score). This question however seems to have fallen in that segment, and I tend to support the undelete here. (But if in doubt I'd respect OP's intent.) $\endgroup$
    – user9072
    Commented Feb 17, 2016 at 13:32
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    $\begingroup$ Minor correction: "if it deletes valuable answers and is not clearly motivated" is closer to what I want to say. $\endgroup$
    – user9072
    Commented Feb 17, 2016 at 13:40
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[UNDELETED]

Unreasonable application of mathematics to the other areas

I may be biased, but the deletion of this question, together with both its answers [and Todd's very pertinent correction], seems an overly drastic action, which I would suggest to undo.

The SE deletion policy, "a post that no longer adds anything to the site should be deleted" does not seem quite applicable here.

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    $\begingroup$ I agree. Closing a question still leaves it visible, and deleting seems uncalled for except in extreme cases. $\endgroup$
    – Lucia
    Commented Jun 30, 2016 at 7:22
  • $\begingroup$ It's not clear to me why answers to the question in question can't just be posted as answers to the earlier linked question 61408. $\endgroup$ Commented Jun 30, 2016 at 23:24
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    $\begingroup$ @GerryMyerson --- I don't know of a way to transfer answers + comment thread from one question to another (put perhaps the moderators have this capability); in any case, I thought that closing rather than deleting the question is the way to proceed with duplicates, isn't this how we have always done it? $\endgroup$ Commented Jul 1, 2016 at 6:35
  • $\begingroup$ What I had in mind, Carlo, was that the people who posted to the one thread could just copy their posts and paste them on the other. Or, someone (you?) could do that for them (giving full credit, of course, and making the answers CW, if desired). But, yes, I think that moderators can do that for questions closed as duplicates. Once the answers are transferred, by whatever means, I'd think the one question could be deleted, no harm done. $\endgroup$ Commented Jul 1, 2016 at 10:58
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    $\begingroup$ @Gerry (and Carlo) Moderators do have the power to merge questions after one is closed as the duplicate of the other. I imagine this functionality is less known since there is simply less call for it on this site. Merging question will delete and lock one of the copies and transfer all comments/answers to the other copy. It is actually used quite a bit on Math.SE. $\endgroup$ Commented Jul 1, 2016 at 18:46
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[UNDELETED] - but at the moment still closed – but now redeleted.

The question

https://mathoverflow.net/questions/277564/computer-aided-investigation-of-zeta-anyone-has-input

is about a certain inequality for the Riemann zeta function which, if true (in a certain domain), is stronger than the RH (in that domain). The question is if this or related inequalities were considered before or about any other insights regarding it. This looks like a good research level question and I don't understand why it was closed or deleted. I propose to undelete and open it.

Update: The question was answered in the comments and I propose to keep it close but not to delete it.

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    $\begingroup$ I've voted to undelete. In the question he links to a preprint of his in the General Mathematics section of the arXiv called "A study of the Riemann zeta function" and he has another preprint there called "A study of Fermat's last theorem". Now, a brief look didn't suggest that either was crankery, but I can understand how people might jump to that conclusion. $\endgroup$ Commented Aug 7, 2017 at 12:38
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    $\begingroup$ About your update: "The question was answered in the comments and I propose to keep it close but not to delete it." This is not really possible unless the question gains some upvotes. A question with negative score and no answer is deleted after 30 days - unless the mods lock the post. Some details are listed in help and further details can be found in the links listed here. $\endgroup$ Commented Aug 8, 2017 at 10:11
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    $\begingroup$ @Martin, indeed, the question has been redeleted by "Community". $\endgroup$ Commented Aug 15, 2017 at 13:35
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[Deleted]

I believe that https://mathoverflow.net/questions/279453/ deserves re-opening, so that the OP can clarify or engage. It might be that the notion of magnitude for metric spaces, for instance, is one that could be relevant for the OP.


Following a reminder from Martin that not everyone can see the original question: here it is in its entirety.

I would like to measure the diversity of a finite (but large) set of points in a metric space.

The average distance does not work, because if the points are concentrated near 2 locations (say, 0 and 1), then the set is not diverse, although the average distance is near 1/2

In comments, the OP goes on to add

I did not find a good formal definition: using the variance or the entropy does not work: a Bernouilli process switching between 2 points has high entropy, but is not 'diverse' intuitively. Taking the geometric mean instead of the arithmetic mean does not improve the situation

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  • $\begingroup$ If some people under 10k are curious what the question is about and cannot see it since it is currently deleted, I will mention that at the moment you can still see the question in Google Cache. $\endgroup$ Commented Sep 3, 2017 at 9:22
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    $\begingroup$ OP was able to clarify or engage while the question was closed (until it was deleted, but that was over a week later). $\endgroup$ Commented Sep 3, 2017 at 11:09
  • $\begingroup$ I'd vote to undelete and reopen if the OP states here the intention to edit and clarify the question. On the other hand, I don't think it makes sense to re-activate an abandoned question. $\endgroup$
    – Stefan Kohl Mod
    Commented Sep 4, 2017 at 8:42
  • $\begingroup$ I have pinged the OP on another question. So maybe he will joint the discussion here and say whether the question is still of interest and whether they can add some further clarifications. $\endgroup$ Commented Sep 19, 2017 at 4:06
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Re-opened and then re-closed

I don't think it is obvious how to find the shortest chord that bisects the area of a convex polygon. That is the question posed in this now closed post: Shortest bisecting line. Perhaps one would have to use the algorithm below, modified to spin the direction through $180^\circ$.

Shermer, Thomas C. "A linear algorithm for bisecting a polygon." Information Processing Letters 41, no. 3 (1992): 135-140.

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The question Why do some mathematicians believe that the notation $(x_n)_{n\in \omega}$ is better than $(x_n)_{n=0}^\infty$ or $(x_n)_{n\in \mathbb N}$ seems to be asked in good faith, even if the tone may have annoyed people who use the notation. It was closed as "primarily opinion-based" but I think that actual practitioners, especially those who work with the von Neumann model/definition of the ordinals, could have sensible answers from which we might all learn something.

I don't use this notation myself, but I have a joint paper where at least one of the co-authors does use this notation.

I think the question deserves to be re-opened and taken seriously.

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  • $\begingroup$ Maybe part of the reason for closure is that the question has been asked anonymously, by a user-xyz. $\endgroup$
    – Stefan Kohl Mod
    Commented Oct 24, 2018 at 23:21
  • $\begingroup$ @jeq this is a tangent, but I don't think the inference "So Occam's Razor tells us that this unregistered user is already a known contributor to Math Overflow" is justified. Plenty of people who are English-speaking academics may have been aware of MO but not actually contributed before asking $\endgroup$
    – Yemon Choi
    Commented Nov 1, 2018 at 23:40
  • $\begingroup$ "deleted by Community♦ yesterday (RemoveAbandonedClosed)" so if it gets undeleted, it will just be redeleted unless it gets some upvotes and/or gets reopened and gets some upvoted answers. $\endgroup$ Commented Nov 4, 2018 at 21:38
  • $\begingroup$ @GerryMyerson Thanks for the reminder. If you look at the question it had a lot of early negative votes but also then some later upvotes $\endgroup$
    – Yemon Choi
    Commented Nov 4, 2018 at 21:57
  • $\begingroup$ At the moment, users below 10k still can see some version of the post in the Google Cache. (However, 10k+ users can check that some votes and comments cam after that version. If I understand correctly how Google Cache works, this version will be no longer be shown after Google crawls that page the next time .) $\endgroup$ Commented Nov 4, 2018 at 23:45
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    $\begingroup$ It seems that the question was posted from an unregistered account and the user what not online since the day they posted the question here, it's not clear whether they are still interested in this. This is probably for a longer discussion, but perhaps a possible alternative would be if somebody else posts a new question; with a link to deleted one - to give credit; and also with a more detailed explanation why the question is interesting - to prevent closure. $\endgroup$ Commented Nov 4, 2018 at 23:52
  • $\begingroup$ I am pretty sure that the question will be treated differently if it is not posted by a new user. (Or I could suggest posting on Mathematics - but I know that Yemon Choi does not have an account there, so in this specific instance it is a less optimal choice.) $\endgroup$ Commented Nov 4, 2018 at 23:53
  • $\begingroup$ It doesn't look deleted to me. Odd. $\endgroup$
    – David Roberts Mod
    Commented Nov 5, 2018 at 1:55
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    $\begingroup$ @DavidRoberts well, someone or something has reopened it at some point between my edit and your comment :) $\endgroup$
    – Yemon Choi
    Commented Nov 5, 2018 at 3:10
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    $\begingroup$ (It's been undeleted but not reopened.) $\endgroup$
    – JRN
    Commented Nov 5, 2018 at 3:18
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[REOPENED]

How slowly can it takes for the Fibonacci terms in a partially permutative self-distributive algebra to stabilize?

How slowly can it takes for the Fibonacci terms in a partially permutative self-distributive algebra to stabilize?

If $(X,*)$ satisfies the self-distributivity law $x*(y*z)=(x*y)*(x*z)$, then define an action of the positive braid monoid $B_{n}^{+}$ on $X^{n}$ by letting $$(x_{1},\dots,x_{n})\cdot \sigma_{i}=(x_{1},\dots,x_{i-1},x_{i}*x_{i+1},x_{i},x_{i+2},\dots,x_{n}).$$ Then $(X,*)$ is partially permutative if for each pair $x,y\in X$, there is some $n$ where $(x,y)\cdot\sigma_{1}^{n}=(x,y)\cdot\sigma_{1}^{n+2},(x,y)\cdot\sigma_{1}^{n+1}=(x,y)\cdot\sigma_{1}^{n+3}$ and if $(x,y)\cdot\sigma_{1}^{n}=(r,s)$, then $(x,y)\cdot\sigma_{1}^{n+1}=(s,r)$.

The motivation behind partially permutative self-distributive algebras is that the quotient algebras of elementary embeddings $\mathcal{E}_{\lambda}/\equiv^{\gamma}$ are always partially permutative (and much more) and because the action of $B_{n}^{+}$ on $X^{n}$ is simplified whenever $(X,*)$ is partially permutative.

I asked this question since I wonder how long it will take for the sequence $((x,y)\cdot\sigma_{1}^{n})_{n\in\omega}$ to stabilize if we know the cardinality of $X$.

Under large cardinal assumptions, we know that for all $N$, there is a finite partially permutative algebra $(X,*)$ and $x,y\in X$ where $((x,y)\cdot\sigma_{1}^{n})_{n\in\omega}$ takes more than $N$ steps to stabilize, but I do not know if one can remove the large cardinal hypotheses from this result.

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Status: [REOPENED]

Request to reopen What is the endgoal of formalising mathematics?

I think it's a good question about an important contemporary evolution of mathematics and found the few arguments to close it not really convincing. It attracted several good answers so far.

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[REOPENED]

An integral representation of the Riemann zeta function was closed, with commenters asking for more information. Author has now supplied the requested information. Perhaps the question should be reopened.

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