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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 was put on-hold pushes the question into reopen review queue, if the edit was done within 5 days of closure. So does a reopen vote. (If the review has already been finished, it is shown on the timeline of the question.) 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 once the request resulted in some action the information Reopened or Undeleted at the start. (If it the action is undone, add this too, like Reopened, reclosed.)

  • Do not only post a request, like "request reopening of ". 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 in a away that takes the feedback the post received into account in a positive way 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 CRUDE is a reasonable place for such requests. The same guidelines apply there.


Earlier versions of this thread that served as a model:

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161 Answers 161

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Reopened

This question asks about the existence of a series $f_i$ of complex functions with several properties: there should exist $x_0$ such that $f_i(x_0) = i$; the sum of the series should converge on some open region to a function $f$; the analytic continuation of $f$ should exist at $x_0$.

It has attracted several answers, some quite detailed, but has been closed as being “not about mathematics”.

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Reopened.

I would like to put forward Model built in Gödel's completeness theorem for reopening.

This question is somewhat vague (as the OP admits), but I think is (i) clear enough to admit a good answer (I have one in mind) and (ii) the sort of question which is difficult to clarify further until one already knows the answer. Ultimately, although it could be improved in minor ways I believe it's definitely a suitable question for this site.

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Undeleted.

Please consider undeleting this post: Help with proof of set theory.

The question asks for clarification of some details in a previous answer of mine. (In a perhaps poorly phrased manner, saying that it seemed there was an error and so the answer was meaningless.)

I took the time to ask in comments for the poster to clarify what precisely was confusing. Then I posted an answer with some additional details.

The poster proceeded to delete all their comments and the question, which I think is poor manners. The question is not terrible, and it may be useful to others.

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  • $\begingroup$ "Reopened"? Shouldn't that be "Undeleted"? $\endgroup$ – Gerry Myerson Jan 30 at 20:25
  • $\begingroup$ Yes it should. 🙂 $\endgroup$ – Andrés E. Caicedo Jan 30 at 20:35
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Undeleted, Redeleted,undeleted, Reopened

This interesting question on Euler's constant was closed then deleted:

Approximating Euler's constant

Please vote to reopen and to undelete. The question got two wonderful answers by @robjohn and @Gary.Now it's completely hidden. And some members can't benefit from the nice answers posted there.

Edit1: Thanks a lot for you help. The question is now undeleted and accessible to all. But we still need two votes to reopen the question.

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    $\begingroup$ Even though I think the post is worth keeping undeleted as it contains useful content, I think it's rightfully closed as it lacks context and I don't understand why you want it reopened (in the actual state). $\endgroup$ – Zacky Feb 21 at 22:39
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    $\begingroup$ @Zacky these questions get very nice answers that's why I think it should be left open. it's because it was open that RobJohn and Gary could answer the question. But my first goal was to undelete the question so it remains accessible to member with low reputation. $\endgroup$ – Aryadeva Feb 21 at 22:46
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    $\begingroup$ This chatroom, GENTLE, might also fit well for your goal in the future too. $\endgroup$ – Zacky Feb 26 at 19:58
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    $\begingroup$ @Zacky Thanks a loot. Will look there. $\endgroup$ – Aryadeva Feb 26 at 20:00
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    $\begingroup$ A +10 answer and a +13 answer, deleted. Vandals. @LostInSpace I hope you can find your way back here, to vote to undelete. $\endgroup$ – Gerry Myerson Mar 4 at 22:47
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    $\begingroup$ It was a nice question with great answers. @GerryMyerson . it's undeleted Gerry $\endgroup$ – Aryadeva Mar 4 at 22:49
  • $\begingroup$ @GerryMyersonYes thank you a vote for undeleting was missing yesterday so I voted and the question is now reopened. Thanks to all. $\endgroup$ – Aryadeva Mar 5 at 23:28
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Reopened

The question Two definitions of tensor product: when are they equivalent was closed as a duplicate of understanding the "tensor product of vector spaces". While both questions ask for a comparison of the standard quotient-of-free-vector-space definition with some alternative definition, the alternative definitions in the two questions are not the same. Moreover, the two questions need different answers: the answer to the first is that, as suspected by the OP, the two definitions are equivalent only in the case of finite-dimensional vector spaces, while the answer to the second is that the two definitions are equivalent, even, it happens, in the infinite-dimensional case. (The main concern of the second question, however, is the "how" of equivalence rather than the fact of equivalence).

Prior to being closed, the first question had received a nice answer, but the poster, fearing the question might be deleted, moved the answer to the second question, where it reads as a bit of a non sequitur, its purpose possibly mysterious to some readers. I'm hoping that if the question gets reopened, the answerer (who recently added a disclaimer to the post) might feel encouraged to move the answer back to the post for which it was intended.

The first question is a pretty fundamental question about the different ways tensor products are defined in various strands of the mathematics literature, and seems to me like a question we ought to have on the site along with some good answers. The second question is concerned with clearing up some misunderstandings about Timothy Gowers' article, How to lose your fear of tensor products, and also seems a valuable question. But clearing up misunderstandings is better done by not muddying the waters with answers to a distinct question that happens to be just similar enough to make things confusing.

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    $\begingroup$ Reopened, but the "Possible duplicate" banner is still there. It doesn't disappear automatically? Someone can/should edit it out? $\endgroup$ – Gerry Myerson Apr 19 at 7:06
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    $\begingroup$ @GerryMyerson I edited the banner out. It seems to be a known bug, occurring when reopening questions that were closed as duplicate when the UI was very different: meta.stackexchange.com/q/193951/313042 $\endgroup$ – Brahadeesh Apr 19 at 9:41
  • $\begingroup$ @Brahadeesh so they've known about it since 2013, and not fixed it? $\endgroup$ – Gerry Myerson Apr 19 at 10:04
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    $\begingroup$ @GerryMyerson Yeah :P There are a lot of bugs that are not feasible for the devs to spend time on, apparently. That's what I gather from browsing Meta SE. $\endgroup$ – Brahadeesh Apr 19 at 10:07
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https://math.stackexchange.com/questions/2659982/does-the-law-of-cosines-contradict-pythagorass-theorem

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

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Reopened

Consider this question: Find the height of a bar, given the lengths of shadows cast by it and another bar

It is closed as a duplicate of a question that is closed with the missing context reason, with no attempt and only one answer. The question I linked has an attempt and the question and many answers are highly upvoted, yet people are voting to delete it, presumably because it's a duplicate. It will require 10 delete votes.

I think we should reopen this question and close the other question as a duplicate of this one. Afterwards, if people are really so thirsty for deletion, they can delete that one.

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Reopened, Closed again, Deleted.

A first-time poster asked about 27 and 37 as repeating decimals. I found the question perfectly clear and on-topic and wrote an answer.

None of the five people who voted to close it as needing “details or clarity” bothered to leave a comment to say what they thought was unclear.

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    $\begingroup$ I'd like to add that I think it's shameful that a first-time poster was treated with such discourtesy. $\endgroup$ – MJD May 30 at 12:50
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    $\begingroup$ I did not remark that close votes must be accompanied by comments. $\endgroup$ – MJD May 30 at 13:30
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    $\begingroup$ The phenomenon is certainly an interesting one to ask for an explanation of...but the asker didn't ask for an explanation. They just asked for a "name for this", and it is quite arguably unclear what they mean by that. There is definitely a good question to be had here (and which you answered), but it's not clear to me that it was asked. $\endgroup$ – Eric Wofsey May 31 at 1:34
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Please consider undoing the duplicate votes here. The duplicate target is quite different as it asks for algorithms while this questions asks for easy ways to calculate determinant (so that careless errors are less likely to commit). The duplicate target is a poor question without context (though with some decent answers).

FYI: It failed the reopening review five times before, as of 3rd Sept. 2018.

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    $\begingroup$ Two points: 1. did you ask the user that put it on hold as duplicate about it? 2. It seems that the answer on the dupe target includes the answer on the original question. // Personally I think the answer given on this question is pretty much besides the point. And the question is very localised. Long story short. I'd delete post. $\endgroup$ – quid Sep 3 '18 at 11:59
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    $\begingroup$ @quid: I didn't (I thought this case is obviously wrong, and it had 4 reopen votes already). I agree that the question is localised and deletion is also a good choice. $\endgroup$ – user99914 Sep 3 '18 at 15:21
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Reopened

Please, consider reopening this question.

The question was somewhat unclear when first asked, but was pinpointed down in comments. I also edited it providing a figure which helps to readily understand the situation.

The context provided by OP (by means of the "planified" picture) makes the source of confusion clear, and now that the problem itself is also clear, I think it fits the site well.

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Undeleted, redeleted, undeleted again, reopened

Statements that look obviously false but cannot be disproved. is at $+15$, and has answers at $+7,+10,+14,+20,+21,+8$, and $+15$. Please consider voting to undelete. [In the interests of transparency, I note that the $+15$ answer is mine.]

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    $\begingroup$ I agree that the question is highly upvoted and has highly upvoted answers. That does not make it an appropriate question for MSE. With regard to what is on-topic, it isn't a problem or puzzle, and I see no clear indication that there is a particular topic that needs to be clarified. With respect to what not to ask, the question seems designed to engender discussion, not to seek explanation. $\endgroup$ – Xander Henderson Sep 27 '18 at 16:35
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    $\begingroup$ For the benefit of the people who cannot see deleted questions, I'll add that this MO question is mentioned in comments: The most outrageous (or ridiculous) conjectures in mathematics. (Even if this one does not get undeleted, the linked MO post might be interesting for people who would consider Statements that look obviously false but cannot be disproved interesting.) $\endgroup$ – Martin Sleziak Sep 28 '18 at 8:42
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    $\begingroup$ @XanderHenderson Just curious, what would you then consider as on-topic for the soft-question and big-list tags? $\endgroup$ – dxiv Oct 4 '18 at 5:51
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    $\begingroup$ Surely we have better things to do that relitigate this post over and over again, and remove the collective efforts of 16 people. I see no harm from the existence of this post, except for the ruffled feathers of people who are inclined to overmoderation. $\endgroup$ – user296602 Oct 4 '18 at 22:13
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    $\begingroup$ In my opinion, if some want content and others do not then it should stay. The veto should be over removal rather than the converse. I will never understand why it's so important to wreck somebody else's party. $\endgroup$ – samerivertwice Dec 1 '18 at 18:22
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Reopened

I request a reopen of Are the corner hypercubera polytopes self-dual?. The question provides a v-definition of an infinite family of polytopes, and asks whether each member of this family is self-dual. (I don't see anything unclear about this question.) Other than being closed for being unclear, I haven't received feedback on this question.

I believe this Q&A provides the first known example of an infinite family of self-dual polytopes that is not a set of k-fold pyramids over a self-dual polytope.

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    $\begingroup$ The post reads as a blog post, not a question. It needs to be vastly more concise, and I frankly don't think that MSE is a good site to ask questions like this; you would do better just talking to someone in the field. You got a bit of feedback in your last meta post. $\endgroup$ – user296602 Oct 1 '18 at 23:20
  • $\begingroup$ Thanks for replying. I agree that a tag pertaining to just a question or two need not exist. As to the question, 1/3 of it is motivation, which I understand to be a requirement of MSE (I would just as soon leave it out). The answer is long because, while conceptually simple, the proof has a lot of tedious parts to it. $\endgroup$ – Dan Moore Oct 2 '18 at 0:35
  • $\begingroup$ I've made my question more concise-it's now about 1160 characters & fits on my small Mac screen. My answer is about 18,000 characters. To analyze why it's so long, I counted the characters in eight distinct parts of the answer. Some parts are long because the thing to be proved requires a lot of words (wishing there was an elegant proof doesn't make it so). $\endgroup$ – Dan Moore Oct 2 '18 at 23:56
  • $\begingroup$ Strictly speaking, the question was closed, not the answer. The Q&A is good because it sets forth the first example (ever in the history of mankind) of an infinite family of self-dual geometric polytopes (one for each dimension d $\ge$ 3) which aren't a set of k-fold pyramids over a self-dual polytope. $\endgroup$ – Dan Moore Oct 3 '18 at 0:00
  • $\begingroup$ I've improved my answer by adding headings, allowing the reader to more easily navigate or skim the answer. $\endgroup$ – Dan Moore Oct 7 '18 at 15:47
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Undeleted.

I nominate Is the numerical range of Identity operator convex? for undeletion because the question asker self-deleted her question shortly after receiving an answer from a high-rep user. That's an abuse of the system.

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Reopened.

This recent Question asks about a variant of the Secretary Problem which as far as I can tell has not been previously answered here.

I mistakenly proposed to close as a duplicate of the classic Secretary Problem, but this variant treats as equally successful the choice of either the best or the second-best candidate. Please consider adding your vote to reopen to mine.

[NB: I edited the title of the post to clarify that this is not identical to the earlier Question, and I discuss in the comments there what little Math.SE discussion there had been on this variant (without supplying its literature references).]

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    $\begingroup$ I've edited the question to refine the formatting and grammar a bit, and to use more gender neutral language. I don't think that the question is all that great (it is a problem statement question with a largely nonsensical "attempt"), but I agree that it isn't a duplicate question, and it is somewhat better than much of the stuff that gets posted. In any event, the question is now open again. $\endgroup$ – Xander Henderson Nov 27 '18 at 2:27
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Undeleted

I nominate Is the Balazard-Saias-Yor integral non-positive? for un-deletion and re-opening. Being self-deleted by a deleted user, it has a score of +1 and two stars. The topic adds value to the site and the question asker has put effort in the post.

Currently, only one undelete vote is needed to undelete this question. I hope the two users who starred this question can see their favorite question re-opened.

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    $\begingroup$ It should be noted that "stars" do not necessarily indicate that a user finds the question useful or up to the standards of the site. Many users use stars to keep track of questions with which they have interacted, and desire to return to at some point. For example, I sometimes star questions which lack context or otherwise fail to meet the standards of this site. After downvoting, leaving a comment, and/or voting to close, I will star the post so that I can return to it a few days later to see if it has been improved. If it has, I'll retract my downvote and/or close vote. $\endgroup$ – Xander Henderson Feb 4 '19 at 17:02
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    $\begingroup$ I'm not saying that this is the case here; I just want to point out that "stars" should not be taken as a sign of quality vis-a-vis undeletion votes. $\endgroup$ – Xander Henderson Feb 4 '19 at 17:03
  • $\begingroup$ @XanderHenderson Thx for comments. Noted. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Feb 5 '19 at 1:27
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Undeleted, closed, deleted, re-undeleted, reopened

I nominate How to use derivatives to prove that $f(x)=2\cos^2\left(\frac{\pi }{4}-\frac{x}{2}\right)-\sin \left(x\right)=1$? for undeletion since OP has self-deleted his/her question after receiving an answer. This is unacceptable on Math.SE.

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  • $\begingroup$ It's better to write self-contained posts. In the current case for the moment there was no big risk, but it's still not ideal. $\endgroup$ – quid Nov 8 '18 at 19:42
  • $\begingroup$ @quid Thanks for your intervention. I'll correct this now. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Nov 8 '18 at 19:44
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    $\begingroup$ I don't understand why this question was closed and deleted by users. It is not unclear what they're asking. (It may not be true, but it is certainly clear!) $\endgroup$ – user1729 Feb 5 '19 at 11:28
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    $\begingroup$ @user1729 Some users don't like wrong info in the question. They have standards so high that $D(\sin x)$ and the RHS of $f'(x)$ doesn't please them. It's possible that they used their power to get rid of this question. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Feb 5 '19 at 11:37
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    $\begingroup$ It's definitely not unclear—the questioner gives the problem, shows what they did, and asks what's wrong with it. I think it could do with an additional answer which makes crystal clear what the error was and how the (interesting!) technique works, and reopening would allow someone to post that. $\endgroup$ – timtfj Feb 5 '19 at 12:06
  • $\begingroup$ @timtfj It's now reopened. $\endgroup$ – GNUSupporter 8964民主女神 地下教會 Feb 5 '19 at 16:04
  • $\begingroup$ @GNUSupporter8964民主女神地下教會 At least it's clear that their expectations could never rise to match the size of your assumptions... $\endgroup$ – Lord_Farin Feb 6 '19 at 17:34
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Undeleted and merged with duplicate

I would like to see the question "Finding sum to infinity" undeleted. The OP says that they "tried using the Taylor series for $e^x$ but couldn’t figure out how to manipulate it to get the above expression", which seems reasonable. Moreover:

  1. The question is a duplicate and is closed as such. It is not standard practice to delete duplicates (see here).
  2. The question itself is on +5 (+6/-1), and one of the answers is on +12.
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    $\begingroup$ I don't get the argument. What is the value of keeping that question on the site? $\endgroup$ – quid Feb 15 '19 at 19:00
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    $\begingroup$ I didn't realiize that "it is standard practice to not delete duplicates." Cite? $\endgroup$ – Gerry Myerson Feb 16 '19 at 4:06
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    $\begingroup$ @GerryMyerson I also had entertained to comment on that. What arguably is true is that "it is not standard practice to delete duplicates", which of course is not quite the same. $\endgroup$ – quid Feb 16 '19 at 12:14
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    $\begingroup$ @Gerry What I meant was "a question should not be deleted simply because it is a duplicate" (so I've edited the post to quid's sentence). This was discussed here. $\endgroup$ – user1729 Feb 18 '19 at 11:28
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Merged

Please Consider undeleting the following question:

https://math.stackexchange.com/questions/3203711/what-are-the-steps-to-finding-int-01-frac-ln1-x-lnxx-dx

Of course, this one is a strict duplicate of the one for it was closed. However, regarding the fact that the answers to this question at all are quite spread I would like to draw attention to my own answer given here collecting some of the possible ways to evaluate this integral within one post.

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    $\begingroup$ Would it make sense to merge the thread with the duplicate target? $\endgroup$ – quid May 4 '19 at 10:11
  • $\begingroup$ @quid That might a better way than undeleting the question, indeed. I'm ashamed to ask, but what exactly does it mean to merge a thread with another one? $\endgroup$ – mrtaurho May 4 '19 at 10:13
  • $\begingroup$ It means that the answers will be moved to the other thread (and deleted on the original one). The Q can be preserved (like a duplicate) or not. $\endgroup$ – quid May 4 '19 at 10:16
  • $\begingroup$ @quid That sounds pretty good. Shall I do this, at least with my own answer, by myself or do I have to request for this somewhere? $\endgroup$ – mrtaurho May 4 '19 at 10:18
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    $\begingroup$ That's something only moderators can do. (Of course you could simply repost your answer on the dupe too, but that would not be merge.) I'll just go ahead and do it now. $\endgroup$ – quid May 4 '19 at 10:23
  • $\begingroup$ @quid Thank you for your time! $\endgroup$ – mrtaurho May 4 '19 at 10:24
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Undeleted

I nominate Factorising the ideal $(14)$ in $\mathbb{Q}(\sqrt{-10})$ into a product of prime ideals. for undeletion since the question asker has self-deleted his/her own question after receiving an answer. This is unfair the answerer who spent time and effort writing the answer, which deserves evaluation from the community.

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Reopened, closed again as duplicate

I nominate reopening Non-negative integer solution for $ax + by = c$. The OP updated the question with what I consider to be sufficient context after the first close vote, but before the final one. As I thought the updated text then made it an appropriate question, I provided an answer. After I discovered it was closed, I flagged it for reopening, but this was declined. FYI, the full timeline is here. Please check this question to see if it should be reopened. Thanks.

Update: As explained in the comments, the question is really a duplicate. It's now closed again for what I consider an appropriate reason, i.e., as a duplicate.

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    $\begingroup$ It's a duplicate of math.stackexchange.com/questions/490602/… and probably several others. If it's reopened, it should immediately be closed as a duplicate. $\endgroup$ – Gerry Myerson May 28 '19 at 6:37
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    $\begingroup$ @GerryMyerson I appreciate your feedback. Since it's a duplicate, I don't have any problem with closing it as such (if it's first reopened), and will even vote to do so. $\endgroup$ – John Omielan May 28 '19 at 6:44
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    $\begingroup$ @GerryMyerson I just gave the last vote to reopen the question. To follow through on what I stated above, I then tried to vote to close as a duplicate. However, because I gave a vote to close on April 18 and then retracted it (due to the OP giving more context so I thought it shouldn't close), the system won't let me vote to close it again, even though it's gone through a close/reopen cycle. As such, perhaps you may wish to start the process of closing it now as a duplicate. Thanks. $\endgroup$ – John Omielan Jun 1 '19 at 3:09
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Reopened

Please consider reopening Does knowing the surface area of all faces uniquely determine a tetrahedron?. This is a very natural and self-motivating question that does not need any additional context, and it's gotten several great answers.

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Reopened

Please consider reopening this post, suitably narrowed since originally closed as "too broad":

Book recommendation... Linear Programming for self-study

I don't believe there has been another such request, and under my pestering the OP has provided context for what sort of self-study they've previously undertaken.

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Reopened

Please consider reopening Does non-uniqueness of solution to 1st order ODE implies the existence of infinitely many solutions?.

This is an interesting question about a not so famous result in ODE. The answers points to the correct reference. I've edited the question to include more context.

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    $\begingroup$ I agree it's an interesting question, and the updated text now has enough context, so I initiated reopening it. $\endgroup$ – John Omielan Jun 18 '19 at 16:36
  • $\begingroup$ @JohnOmielan, if you care, please consider also editing the answer there (to rollback to edit 1). Now that the post is reopened, there is no need for that comment. I tried to edit myself, but the suggested edit got rejected $\endgroup$ – Arctic Char Jun 19 '19 at 19:20
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    $\begingroup$ I agree the comment there regarding it being closed is no longer pertinent, so I did rollback of the edit. $\endgroup$ – John Omielan Jun 19 '19 at 19:26
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Undeleted (and edited the duplicate target)


Please undelete this post:

Three coins are tossed. If one of them shows a tails, what is the probability that all three coins show tails?

This question was marked as a duplicate to another question (created 2014) that was closed and deleted (2018).

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    $\begingroup$ It seems it took 9 votes to delete this question. I suppose that's because it had 30 upvotes? Anyway, currently it has 7 undelete votes. Does it need 9 to undelete? $\endgroup$ – Gerry Myerson Jul 5 '19 at 5:52
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Undeleted, reopened

Please consider undeleting and reopening this post:

How does one prove the inequality $1+|x|\le (1+|y|)(1+|x-y|)$?

OP clearly indicated the context of his/her question: it is from a proof in Wolff's lecture notes on harmonic analysis.

[Added upon request: this post has also been edited into a (more) decent one.]

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    $\begingroup$ If you edit a post significantly indicate so in the request. I have no problem with it by itself, but since such actions are quite frequently overlooked by observers it can lead to the false impression that a relatively decent post was deleted. $\endgroup$ – quid Jul 8 '19 at 14:07
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    $\begingroup$ @quid If someone else (not OP) edits OP's question to make the question 'fit' on MSE, then does the question gets reopened or undeleted always? $\endgroup$ – allesia_b Aug 9 '19 at 18:48
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    $\begingroup$ I said different by OP because sometimes the question is old, say 2015, and OP hasn't visit MSE since 2015. $\endgroup$ – allesia_b Aug 9 '19 at 18:51
  • $\begingroup$ @Isa I'd say yes for the most part (although what 'fit' mean of course leaves room for interpretation). That said, some users do not like the practice, thus there can also be push back. But in abstract and as a general principle (there can be exceptions in special cases) if a question is a good fit for math.se we usually keep it around no matter how it arrived in this state.// If you want to discuss this in more detail please open a separate thread. $\endgroup$ – quid Aug 9 '19 at 19:32
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Undeleted, reopened, closed

Please consider undeleting this post:

How to find ${\large\int}_1^\infty\frac{1-x+\ln x}{x \left(1+x^2\right) \ln^2 x} \mathrm dx$?

This is not a trivial exercise and OP shows his/her thoughts that "Routine textbook methods for this complicated integral fail." It has several very well-written detailed answers with rather high number of upvotes.

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    $\begingroup$ '[S]hows his/her thoughts that "Routine textbook methods for this complicated integral fail."' That's not relevant context. Most likely it's a constructed challenge and should have been declared as such. This type of post borders on a misuse of the site. The following comment at score 13 is relevant I feel like it's becoming a trend to ask questions about practically impossible integrals. $\endgroup$ – quid Jul 8 '19 at 19:34
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    $\begingroup$ You think "That's not relevant context." And this proposal focus particularly on undeleting the post. Considering THREE high-quality answers (4+31+40 upvotes) that already existed I find it ridiculous (yes, this is my rant) to delete this OLD post. If there is any misuse of this site at all, the deletion, in this particular case, IS misuse of the privilege of votes. [mod redacted] $\endgroup$ – Jack Jul 8 '19 at 19:58
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    $\begingroup$ Bringing up other users in this form is out-of-line, in general. In the specific case it's also highly misleading. (I removed it.) $\endgroup$ – quid Jul 8 '19 at 20:24
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Reopened

Prove: there exists 3 sets: $A, B, C \subseteq \mathbb{N}$ such that: $A\cap B\cap C =\emptyset$ and $|A|=|B|=|C|=\aleph_0$?

Please consider reopening my question as I've edited it in order to explain the full context of it.

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    $\begingroup$ The current status is only to be added after a change occurred. In any case it should always be the current status of the post not the requested action. $\endgroup$ – quid Aug 15 '19 at 13:19
  • $\begingroup$ I understand. thank you for the help $\endgroup$ – Jneven Aug 15 '19 at 13:20
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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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