# Requests for Reopen & Undeletion Votes (volume 07/2018 - today)

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:

Reopened

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

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

Reopened

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

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

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.]

• 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. – Xander Henderson Sep 27 '18 at 16:35
• 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.) – Martin Sleziak Sep 28 '18 at 8:42
• @XanderHenderson Just curious, what would you then consider as on-topic for the soft-question and big-list tags? – dxiv Oct 4 '18 at 5:51
• 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. – user296602 Oct 4 '18 at 22:13
• 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. – samerivertwice Dec 1 '18 at 18:22

Undeleted

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

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

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

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

(Edit: comment removed)

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

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

Undeleted

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

Reopened

(This is to break this request post into two)

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

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

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

Reopened

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

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

Reopened

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

Undeleted and reopened

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

Reopened

Please consider reopening the following question:

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

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

Reopened

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

Reopened

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

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

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

Undeleted, redeleted, re-undeleted, reopened

Please consider reopening the following question:

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

OP clearly indicates his/her attempt in the post:

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

This is not a zero effort question.

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

Reopened

I nominate A question of arithmetic regarding erection cost of a structure. for reopening since the question asker has shown his/her work in solving the problem.

• I agree, but think they should also be encouraged either to edit what they said in comnents into the question, or to give someone else permission to do so. – timtfj Feb 5 '19 at 12:20

Undeleted, put on hold, deleted

Please undelete https://math.stackexchange.com/q/3209899/290189 since OP self-deleted her own post after receiving an answer. This is an abuse of the system.

• I undeleted it. Please try to use correct terminology. Undelete and reopen are not the same. – quid May 2 '19 at 7:33
• @quid Thanks for your undeletion and reminder. I'll be aware of that next time. – GNUSupporter 8964民主女神 地下教會 May 2 '19 at 11:49
• Question is currently on hold. – Gerry Myerson May 3 '19 at 3:06
• @GerryMyerson Thanks for notification. Status updated. – GNUSupporter 8964民主女神 地下教會 May 3 '19 at 6:52

Undeleted and closed as duplicate

Choose 2 good batteries out of 8 (4 bad 4 good) was deleted by its author, after an answer was posted. This is considered to be an abuse of the system.

Full disclosure: the only answer posted before the self-deletion was mine.

• Currently closed as a duplicate. – Gerry Myerson May 3 '19 at 3:07

Undeleted

Please undelete A probability to 6 in a dice since OP has self-deleted his/her own question after receiving an answer. This isn't fair to the answerer because his answer deserves review from the community.

Please undelete A contradiction in calculating the legendre symbol and https://math.stackexchange.com/q/3224172/290189 because OP's have self-deleted their question after receiving an answer from others.

• I undelete both. At least for the one, it'd also have been possible to let it deleted as it was a relatively simply oversight. It's not clear there is any value in keeping that around. But there is also no harm, so. – quid May 14 '19 at 15:31
• Please adhere to the "one request per answer" format; having multiple requests in the same answer makes it difficult to track changes. – Brahadeesh May 15 '19 at 8:03
• @Brahadeesh Thanks for your comments. I'll beware of this practice next time. – GNUSupporter 8964民主女神 地下教會 May 15 '19 at 9:00

Undeleted.

Please undelete Bounding the number of edges in a graph satisfying a certain property since the question asker has self-deleted his/her question after receiving an answer.

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

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

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

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

Undeleted

Intersection of Normal closure and Center

The OP deleted question after answer was given.

• I undeleted, but maybe write a proper answer next time. – quid Jun 4 '19 at 13:39
• @quid I like hints (plus its a pretty straightforward question - I spent a while debating whether to just leave it at "kill $t$"). – user1729 Jun 4 '19 at 13:43
• Then maybe start a Q&H site. This is Q&A site. – quid Jun 4 '19 at 18:09
• @quid the hint was clearly sufficient for the OP - they wouldn't have deleted their question otherwise! :-) – user1729 Jun 4 '19 at 19:00
• That's pretty irrelevant to my point. Further, If "sufficient for the OP" is your main concern, why do you bother us with an undelete request? // The way that hint was orginally presented to me personally made it pretty confusing. The new format is in a way better. But, frankly I just despise that form. I know it's popular but I think it's terrible style. – quid Jun 4 '19 at 22:55

Reopened, closed

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

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

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

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

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

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

Thank you!

Undeleted, Reopened

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

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

Undeleted, reopened, closed

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

Undeleted, deleted, undeleted, deleted (mod)

Please consider casting the final undelete vote to this post:

Which among the given series converges

This is not a zero effort post: OP has ruled out some choices for the problem and has reduced the problem to a simpler one. This is a good attempt. Also, @Theo Bendit has posted a well written answer.

Mod comment (quid): I deleted it as the question remains unclear in its formulation. As such it has the potential to create confusion and in any case the mathematics is well-known and in one way or the other certainly on the site. It is good that OP apparently got competent help. This does not alter the fact hat preserving the thread as is in my opinion does not ad value to the site and to the contrary degrades it (adding a confusing question). If somebody want to preserve the answer they should have improved the question, or create a separate one. That's still an option.

• The asker has not ruled out several choices for the problem. The problem is not a multiple choice question. Rather, they were asked to examine each of those four series, and determine which converge. If anything, the question is four distinct true / false questions (making it "Too Broad"). – Xander Henderson Jul 28 '19 at 16:18
• Moreover, you claim that it is not a zero effort question. Even if I agreed with you regarding the idea that "showing effort" is, in and of itself, sufficient context, I disagree about the effort which has been shown. The question is ultimately about one of the four series being presented, and there is no work shown for that series. For the remaining three, the asker claims to have already found appropriate counter-examples, but don't actually show any of that effort. Claiming to have done something is not the same as demonstrating it. – Xander Henderson Jul 28 '19 at 16:18
• "The problem is not a multiple choice question. ... which converge." One could turn almost all the multiple choice problems into non-multiple-choice ones in such a way. The rest of your comments are based on this biased assumption. "the asker claims to have already found appropriate counter-examples, but don't actually show any of that effort." OP summarized as partial work that three items haven been done and now he/she focuses on item (c). Not guilty. The strong action of deletion of this post is unreasoning. – Jack Jul 28 '19 at 17:30
• The question consists of four different T/F questions. It is not a single multiple choice question. There are four different questions here. Determining the truth or falsity of parts (a), (b), and (d) does absolutely nothing to shed light on (c), especially considering that the asker doesn't actually show any of their work, but simply states that they have already completed those parts. It lacks context and is too broad. It was rightfully closed and deleted. – Xander Henderson Jul 28 '19 at 18:16
• One has to wonder how they could show b yet not c. Makes one wonder of the merits of their undisclosed approaches. The paraphrase in meta OP is false as pointed out by @XanderHenderson and your reply is strange in that the critique of you paraphrase (not even the main OP) was not that the question is a multiple choice question but rather that there is not partial progress to the question asked. The best one can say is that the question is not 'several questions asked in one' (contrary to what one might think) and the Q provides some limited context by giving related problems they can solve. – quid Jul 30 '19 at 11:47
• I'd say if they had sketched their solutions to those they can solve, it might be sufficient context. As is, it does not add all that much, especially since the partial progress is implausible. Indeed it appears it is partly false as they might have misunderstood the question (the meaning of necessarily). Of course, it's anyone's guess since they do not provide the claimed solutions. Clear case of actual lack of context; we cannot identify the extent of the problems of OP. – quid Jul 30 '19 at 11:50

Undeleted, deleted, undeleted, deleted, undeleted, deleted, undeleted, delete (mod)

Please undelete this post Map subset of a group to zero?

This is not a trivial exercise. It has a very detailed thoughtful answer by @Arturo Magidin.

Mod comment (quid): I deleted this one, as the question-post is still not clarified and the thread including the answer post is a back and forth. Like: "It cannot be this, you may mean that. Oh, now you said it's about something else." I am glad that OP was helped, but I think there is no archival value to this in its current form. As usual, those that want to can extract whatever they think is valuable, via edits or moving of content.

• If you plan to keep saying things like "Redeleted (6/17/19) by a same group of users. One initiated three times the delete votes and one voted three times to delete this post. – Jack Jun 17 at 22:01" you might refrain from voting to undelete repeatedly, especially on posts where there was not recast delete vote prior to that. (There is now though.) – quid Jul 13 '19 at 15:43
• There has been no action whatsoever (to my knowledge) from mods or the system to prevent casting/initiating deletion votes for some particular posts over and over again by mostly same group of users. It is not difficult to count such instances. I assume from such observation that repeated voting is not discouraged in general. "If you plan to keep saying things like" This is an absurd and highly misleading comment from a moderator: your quoted comment refers to one particular proposal and I have never said it somewhere else. – Jack Jul 13 '19 at 18:09
• I take it you do not plan to keep saying things like the one I quoted, then. Well you did say "On the other hand, what one can see from the timeline is that a user voted to delete the posts twice while there are people who hold different opinions have already voted to undelete and reopen the post." which also raises double-voting in a critical way. – quid Jul 13 '19 at 18:57
• There has been no action whatsoever from mods or the system to prevent casting/initiating undeletion votes for some particular posts over and over again by mostly same group of users either. – Jyrki Lahtonen Jul 14 '19 at 16:26
• @quid I think a mod deletion was highly improper here. Sad to see you once again forcing your personal opinions onto the community. These decisions should be made by the community - not an individual. – Bill Dubuque Aug 4 '19 at 15:24
• @Bill after about ten changes of status I think it's about time somebody decides it one way or the other. Visibly the community did not reach a solution. – quid Aug 4 '19 at 15:26
• @quid "Changes of status" are not harming anything. There have been more in the past and they eventually settled down. – Bill Dubuque Aug 4 '19 at 15:27
• @Bill it's a distractions, possibly confusing, and bumps this meta post. Certainly there are worse things, but I consider it as fundamentally unreasonable to have "blinking" posts that are un-deleted every other day or every other week. (This one is going on since a month.) – quid Aug 4 '19 at 15:29
• @quid I think there are for more important matters that deserve to be deemed "fundamentally unreasonable". This shouldn't even be on the radar. – Bill Dubuque Aug 4 '19 at 15:32
• @BillDubuque examples? – quid Aug 4 '19 at 15:33
• @quid One of the reasons that I initially created this thread (original version) was so that there would be only one thread being bumped on such matters. The bumps are expected and are completely normal. Those with no interest in such matters can easily ignore it. – Bill Dubuque Aug 4 '19 at 15:42
• @BillDubuque that's fine it does however not address the other points and does not provide any examples. Anyway, if you see things that I or another moderator should address please bring them to our attention. If you want to discuss this particular post in more detail, post a question about it. – quid Aug 4 '19 at 15:49

Deleted, undeleted, deleted, undeleted, deleted, undeleted, reopened, closed as duplicate, deleted, undeleted

What OP wrote under the problem statement clearly show his/her thoughts:

How can I do this if I don't know how $$a_n$$ is defined? I can use the given limit to get the range of $$a_n$$ in terms of $$L$$, but I lack the direction to complete the proof.

This is not a zero effort question. Please consider undeleting this post:

Given positive sequence $$a_n$$ where $$\lim _{n\to \infty} a_n = L, L >0$$, prove that $$\lim_{n \to \infty} 1/a_n = 1/L$$

• Did you check if it's a duplicate? It's a very standard question. – quid Apr 26 '19 at 14:32
• @GerryMyerson a question might be eligible for closure for multiple reasons. It's maybe not a PSQ in it's purest form, but it's still not a good question. I'd say if somebody wants to restore a question it's on them to make sure no reason applies not just the one that was chosen. Further, it would have been on the asker to make some good faith effort to find a dupe before answering (and then complaining that their answer was removed). If a dupe of this question is not findable what does this tell about the level of organization in those tags. The priorities are not good. – quid Apr 27 '19 at 7:12
• @GerryMyerson here math.stackexchange.com/questions/1171733/… it was pretty trivial to find. – quid Apr 27 '19 at 7:22
• Well, in any case they complain. We can replace the "that" by "after". On the rest, again the onus is on them. They ought to explain that there is no dupe (supposedly). Further, it is generally considered as good form to mention if one has answered oneself. Especially if it is the only answer. @GerryMyerson – quid Apr 27 '19 at 7:26
• @GerryMyerson not sure about that. I might have had the luck to use the better strategy for that example, searching for words via Google on this site not for formulas for example 'convergence of inverse of convergent sequence' works well. – quid Apr 27 '19 at 7:31
• @GerryMyerson (and quid) I did try to find a duplicate and I indeed noticed that limit of reciprocal of a sequence away from zero should be a rather standard exercise in calculus/analysis and should have been asked before. However, I think "context" counts as an integral part of a post, and that is why we insist on "contexts", don't we? [cont.] – Jack Apr 27 '19 at 13:14
• [cont.] I am not able to find any same/similar confusion ("How can I do this if I don't know how $a_n$ is defined?") in any known post, for instance in the linked post in one of quid's previous comments and thus I do not think this post should be considered as an "absolute" duplicate that one should delete it. – Jack Apr 27 '19 at 13:14
• I agree with Jack's comments above, I don't think this post should be closed if a duplicate is not found where the same confusion is addressed. To the best of my knowledge, this confusion has not been addressed before, so this post should be undeleted and reopened. – Brahadeesh Apr 28 '19 at 5:43
• @GerryMyerson Basically a duplicate, except it doesn't require $a_n$ to be a positive sequence, was asked fairly recently at Sequence Limit Reciprocal Law Proof, where I provided an accepted answer. As for finding it, note it originally only used the tag "elementary-number-theory", but I changed it later to "limits", so searching for it initially might not have turned it up. However, I can't see the original deleted question content, but the page it brings up shows $2$ other somewhat related ... – John Omielan May 2 '19 at 8:08
• (cont) questions: Given: $\lim\limits_{n\to\infty}a_n=0$ prove $\lim\limits_{n\to\infty}\frac{1}{a_n}=\infty$ and How to formally prove that if $\lim \limits_{n \to \infty}a_n=\infty$, then $\lim \limits_{n \to \infty}\frac{1}{a_n}=0$.. Although they're somewhat different, and I haven't checked them carefully, I suspect their techniques are transferable. – John Omielan May 2 '19 at 8:09
• The status of the question had not changed at all. What is the justification for this edit? – quid May 31 '19 at 16:57
• On the comments above, which I only see know, due to lack of a notification, that's not a particular confusion. Any generic proof will necessarily do just fine to address this. I mean the proof you gave is completely generic. What do you think you did to address whatever specific confusion? – quid May 31 '19 at 17:04
• I agree with Brahadeesh's comment and I've undeleted the question. – GNUSupporter 8964民主女神 地下教會 Jun 14 '19 at 9:21
• @quid The quoted question in Jack's last comment answers your first question; point (3) in Jack's answer addresses your second one. – GNUSupporter 8964民主女神 地下教會 Jun 16 '19 at 3:17
• @GNU As detailed this ask nothing more than that the author understands that they might be able to do it or at least how to strat for a specific sequence like say $2n/(n+1)$. Any generic proof will do just fine, and what about the third point? Again any proof will have to address this somehow (in one based on continuity it might be hidden). Certainly it's findable in other answers. It's just a contrived argument to save this post, and frankly I am appalled by this. Explain how this answer math.stackexchange.com/a/1171755 is not sufficient or math.stackexchange.com/q/54754? – quid Jun 16 '19 at 8:51

Undeleted, deleted, undeleted, locked and merged with duplicate (mod)

Please consider undeleting: How to count the number of good permutations?

This is not a duplicate and has a good answer.