# 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:

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 at 0:26
• It seems to be redeleted. – Brahadeesh Apr 30 at 3:58
• 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 at 15:42
• The real missing context is the source and motivation of the problem. – Carl Mummert Apr 30 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 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 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 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 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 at 19:06
• @GNU what exactly should have been funny? You tried to ridicule others. – quid May 2 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 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 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 at 21:36
• 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 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 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 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 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 at 11:49
• Question is currently on hold. – Gerry Myerson May 3 at 3:06
• @GerryMyerson Thanks for notification. Status updated. – GNUSupporter 8964民主女神 地下教會 May 3 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 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 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 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 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 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 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 at 13:43
• Then maybe start a Q&H site. This is Q&A site. – quid Jun 4 at 18:09
• @quid the hint was clearly sufficient for the OP - they wouldn't have deleted their question otherwise! :-) – user1729 Jun 4 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 at 22:55

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, 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 at 15:32
• @BillDubuque examples? – quid Aug 4 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 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 at 15:49

Undeleted, reopened, closed

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.

• '[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. – quid Jul 8 at 19:34
• 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] – Jack Jul 8 at 19:58
• 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.) – quid Jul 8 at 20:24

Undeleted, reopened, closed, deleted, undeleted

Please consider undeleting the following question:

What about irrationality of $\int_1^\infty\frac{1}{\sqrt{\Gamma(x)}}\mathrm dx$?

I agree on the reason for closing this question. Even though the post is somewhat strange in its wording it appears to be overall interesting for the community (as the upvotes outweigh the downvotes resulting in a balance of $$+6$$). Additionally, the integral appearing in the question is strongly related to the Fransén-Robertson Constant and might be of help as future reference for this topic (as a number of relevant posts is also linked with the deleted one).

The question has got deleted again. I have still my POV listed above and I would like to hear the reason for re-deleting the question.

• I voted to undelete, but I have to say, it's a highly undermotivated question. I could write down a thousand expressions evaluating to real numbers, and ask for each, whether it's rational, without giving any reason to think it is, or any reason to be particularly interested in whether it is. – Gerry Myerson Jul 29 at 23:40
• @GerryMyerson I have to agree on this issue. And indeed, the motivation is clearly missing but what remains is a relation to an actual known constant, which is from my POV the only thing which makes this question worth keeping. – mrtaurho Jul 30 at 10:03
• OP has shown no interest in the question, having refused the invitation to improve it. mrtaurho, I suggest you post an improved version of the question, and your answer, so the material won't be lost. – Gerry Myerson Aug 11 at 23:13
• @GerryMyerson Thank you, for your response. I will do so, as soon as I have time! :) – mrtaurho Aug 11 at 23:16

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.

• 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. – quid Aug 15 at 13:19
• I understand. thank you for the help – Jneven Aug 15 at 13:20

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.

Reopened, undeleted, closed

Please consider undeleting the following question where I also provided an answer.

The OP from clearly provides background on how the integral appeared, although it was some kind of homework now it can be useful for others too.

• It's good form to disclose that one has an answer on the post oneself. – quid Aug 15 at 20:59
• Hope I don't sound rude, but I don't understand what you wrote even with translate. Did you meant: It's a good thing to mention that I posted an answer to the linked question? – Zacky Aug 15 at 21:07
• Yes. You should mention this. It makes clear that you are not a neutral third party. You have a personal interest in the undeletion. This does not disqualify you from making the proposal. But it is good form to be upfront about it. – quid Aug 15 at 21:12

Undeleted

Please consider undeleting and reopening this post: radical center of three circles.

This post clearly indicated an attempt and has a detailed answer.

Undeleted, then closed and deleted

I think there's a consensus that we undelete questions when they are deleted by the user who posted them after someone else has posted an answer (see, for example, the comment here: https://math.stackexchange.com/questions/2759560/extending-the-triangle-inequality#comment5694741_2759560). In accordance with that consensus, I propose undeletion of https://math.stackexchange.com/questions/2840649/solutions-to-sum-j-ok-r-j23r-j2-equiv-0-mod-p

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

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

Reopened

Prove $\lim_{z \rightarrow z_o} f(z) \in \mathbb{C}$ if $\lim_{z \rightarrow z_o} (z-z_0) f(z) = 0$

I made a new question, where I tried to be as clear and narrow as possible.

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

Reopened

There have been at least five questions asking how to prove instances of the general proposition $$\log_m(m + 1) > \log_n(n + 1)$$ for integers $$n > m > 1$$:

1. How to know if $$\log_78 > \log_89$$ without using a calculator? (3 May 2012), with an exemplary answer by user22805.

There have been at least three other questions asking to prove inequalities of the form $$\log_a{b} > \log_c{d}$$ for integers $$b > a > 1$$ and $$d > c > 1$$:

There has also been at least one more complex question in the same broad category:

Most recently, the following question was posted, but it was quickly closed as a duplicate (I confess to being one of those who voted to close it):

10. Comparing logarithms with different bases (23 Oct 2018).

The close message for question 10 reads:

This question already has an answer here: How to compare logarithms $$\log_4 5$$ and $$\log_5 6$$? 6 answers

But the only method used to answer a previous question (1-9) that can also be applied to the present question (10) is to find positive integers $$m, n$$ such that $$b^n > a^m$$ and $$d^n < c^m$$ (as in Eudoxus's theory of proportion), so that $$\log_ab > \tfrac{m}{n} > \log_cd$$.

In a comment (which has now been incorporated into the text of the question), the questioner showed that he was aware of this method, and had already used it to answer his own question. He continues:

However, that method doesn't work for every example, and I wonder if there's a easier way to solve this?

Strictly speaking, any logarithm comparison question could be answered in this way. But that is not always very practical, because one one has to search for suitable values of $$m$$ and $$n$$, which may be quite large. Some previous answers state or imply the general rule that $$\log_a{b} > \log_c{d}$$ if $$\tfrac{b}{a} > \tfrac{d}{c}$$ and $$a < b$$, but that rule does not apply in this case. It is interesting to ask if some other rule might be applied, eliminating the need for a possibly haphazard search for $$m, n$$. Failing that, ad hoc solutions to the present problem are also of interest.

Question 10 meets MSE's selection criteria, so it ought to be reopened.

• The question lacks contract in any event. Most importantly: why were the specific constamts in the problems chosen? If the problem is about arbitrary constants, it should be rewritten to say so. If the OP was already aware of a method to solve the problem, that context should also be in the post. Overall the post does.noy seem to demonstrate much effort to write a good post. – Carl Mummert Oct 28 '18 at 16:19
• @Carl On that basis, Diophantus would have a hard time posting a question here! Where, in MSE's rules, does it say that every question must be framed in the most general terms possible? What is wrong with asking a question about particular numbers? Especially as no-one has (yet) posted a general answer or a general question covering this particular case. Finally, even if it were granted (purely for the sake of argument) that an experienced user ought to have asked a more elaborate question, shouldn't a new user be cut some slack? – Calum Gilhooley Oct 28 '18 at 16:28
• @Carl Also, it was closed as duplicate, and my point is that it is not a duplicate. The close message is a false statement, and the close decision should be reversed. (Of course, anyone can also vote to close it for another reason, and no such person need feel obliged to vote for reopening.) – Calum Gilhooley Oct 28 '18 at 16:34
• !Calum: there's no problem posting a question with specific numbers - but it is up to the OP to include adequate context, and the reason for choosing seemingly arbitrary numbers is (in my opinion) part of that context. If this was asked person to person at a department tea, we would expect the asker to say something about the numbers involved. The OP should be encouraged to improve the problem, they have plenty of "slack" to do so. – Carl Mummert Oct 28 '18 at 21:19
• I think my guilty conscience over this has now been assuaged. :) – Calum Gilhooley Oct 29 '18 at 0:36

Deleted by a moderator

This question was closed and deleted with the reason given "This question is missing context or other detail". However the author of the question explained both his educational background (he is an undergraduate) and his motivation for the question (it was information that wasn't covered in his degree).

This information is sufficient context to give an answer, indeed I can't think of any further context that a person asking the question could add that would result in a better answer.

• The body does not even contain the question. That question-post is poor, and the thread of very limited value overall. The answers being pretty terse and not giving enough detail. // Added: Given the comment below I'll add that it was not I that deleted it. – quid May 9 at 6:59
• As far as I can tell, if a post was deleted by a moderator - like in this case - the deletion cannot be reversed by regular users. (Of course, voting your posts still can show to which extent users support undeletion - and if there is some support, perhaps moderators might have a look at the the question again.) – Martin Sleziak May 9 at 6:59
• @quid can you explain what is poor about the question? Broadly speaking pen and paper methods of factoring numbers is a subject that the site should have coverage of. – Q the Platypus May 9 at 23:32
• I already mentioned one shortcoming. Further and more drastically, the question does not contain any relevant thought of the OP or even just explanation what they want that information for. For example, do they realize that one can easily recognize that some number are not prime? How would they approach the problem for two digit numbers? Or something else, would all make the question better. That said, the question would arguably be saveable. But what for? The answers are low quality. I'd prefer somebody, say my students, won't find any information here rather than those answers. – quid May 10 at 9:55
• Fortunately similar information is available in other and better threads. In my opinion, the site is quite simply better without this thread. – quid May 10 at 9:57

Undeleted, reopened

Please consider undeleting this old post: Show that a function $$f:P(X)\to P(X)$$ preserving the subset relation has a fixed point

It was created on Sep 17 '16, has two good answers.

• It seems to be a special case of this question, and Aloizio's anwer in fact answers the general question. So if the goal is to preserve answers, the logical thing to do would be to move them there. – Arnaud D. Jun 28 at 13:48
• It seems to me the Question at issue here has the more general formulation (it does not require an "increasing" function). In any case I've voted to reopen as the Question at issue meets my threshold for context (and it otherwise also on-topic). – hardmath Jun 30 at 19:45
• I disagree with your assertion that the question has two good answers. It has one good answer, and a hint. The question itself is not good at all. I am content to see the question left undeleted, but I see no reason to reopen it. Arnaud D.'s suggestion is, I think, preferable. – Xander Henderson Jun 30 at 23:51
• "I am content to see the question left undeleted." Well, that is what my proposal is. I agree that the question itself was not good enough and thus I did not ask for reopening. @Martin Sleziak has added useful information to the post. (Thanks!) Also, Aloizio's good answer mentions at the beginning "the nice answer by @Brian". – Jack Jul 1 at 1:47

Undeleted, deleted, undeleted, reopened

Please consider undeleting this post: What is the formula of this angle?

There is a well written and well-received answer to this interesting question.

Undeleted, deleted, undeleted

Please undelete and consider reopening this post: Show this equation has every positive integer as solutions

OP did give his thoughts. NOT a no-context question. And there are two good answers.

Undeleted, deleted, undeleted

Please consider undeleting this post: How to evaluate $$\lim_{x \to 3} (x^2-5x+4)^{x-3}$$, which is clearly not a zero-effort question.

• You say that the question should be opened because it is "clearly not a zero-effort question." This seems to imply that the question was closed because it "lacks effort". However, "lacks effort" is not one of the close reasons used on MSE. Indeed, I see that question was closed for "lacking context". For example, a description of what theory the asker is familiar with and what course they are taking. Are they expecting a computation involving $\varepsilon$s and $\delta$s? L'Hospital's rule? What? The question should be deleted. – Xander Henderson Aug 15 at 12:31
• Moreover, examining the comments attached to that question, it is not even clear where the function being discussed is meant to be defined. Is it a real function with a very "hole-y" domain? or a complex function, in which case one needs to consider branches of the logarithm? It is not a good question. – Xander Henderson Aug 15 at 12:34

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 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 at 7:12
• @GerryMyerson here math.stackexchange.com/questions/1171733/… it was pretty trivial to find. – quid Apr 27 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 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 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 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 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 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 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 at 8:09
• The status of the question had not changed at all. What is the justification for this edit? – quid May 31 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 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 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 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 at 8:51

Undeleted, deleted, undeleted

I nominate Optimization problem for routes for undeletion because the question asker self-deleted his question shortly after receiving an answer.

• Is that the right link? The question asker is named Jacob, which I take to be a male name, and the question was undeleted at the same time as this answer was posted. – Gerry Myerson Feb 6 at 21:03
• @GerryMyerson Nice catch! I was typing on 📱, and I made this careless mistakes. I'm going to update this status of my answer. – GNUSupporter 8964民主女神 地下教會 Feb 6 at 21:08

## protected by Community♦Oct 1 '18 at 14:49

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