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$\begingroup$

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

Please post general requests for reopen votes as answers below.

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

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

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

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

(Improvements on the phrasing are welcome.)

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  • 4
    $\begingroup$ Not entirely necessary. There's a reopen queue now. A closed post can be put into the reopen queue by editing or voting to reopen. 3k+ users can vote to reopen (or alternatively vote against it). If this mechanism fails, then one can open a separate meta post about the question. I find that this is a more efficient process :) $\endgroup$ Jun 27, 2013 at 21:10
  • 5
    $\begingroup$ @Manishearth: Not everyone has access to the queue history, so not everyone can tell when a thread has been "outlived its review" and it is time to come to meta. In the long run, I think it's better to have one post for "run of the mill reopen votes" rather than having more and more separated questions whose answers would consist mostly of "Done." $\endgroup$
    – Asaf Karagila Mod
    Jun 27, 2013 at 22:06
  • $\begingroup$ @AsafKaragila Yeah, I see your point -- but "outlived its review" can just mean "wait a day", regardless of its queue status. So, if a reopen vote or edit doesn't push it out of the queue in a day, then come to meta (and post on this post, or separately -- IMO separate meta posts lead to better discussion, but that's just me). But if you take a look at the MSE post: Most of the recent ones are either obvious nos (closed post) user whinging about closed post, or obvious yes's (Awesome edit improved post). $\endgroup$ Jun 27, 2013 at 22:31
  • 2
    $\begingroup$ These can be dealt with fairly within the review queue itself; giving an explicit platform on meta for people to whinge or where people feel obliged to post obvious reopens is imo unnecessary. Again, I don't know much about MO or MSE, so I could be grossly wrong here :). Just giving an outsider's viewpoint. $\endgroup$ Jun 27, 2013 at 22:32
  • 2
    $\begingroup$ I agree with Manishearth: with the new "on-hold" -> edit -> add to re-open review queue mechanism, threads like this should be much less necessary. $\endgroup$ Jun 28, 2013 at 9:21
  • $\begingroup$ @AsafKaragila Btw, this is why doing it separately is imo better, you get a lot more feedback and discussion. $\endgroup$ Jun 28, 2013 at 16:59
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    $\begingroup$ I dont want to interfere here with anything but I disagree with Manishearth about the usefulness of this Request to Reopen List. At Math SE I have observed that it works very well and efficiently to get questions reopend without making much fuzz about it. At Physics SE, we controversely discuss each question that somebody thinks should get reopend at meta seperately at length with the effect that people just discuss instead of just doing it, and almost nothing gets reopend at the end. $\endgroup$
    – Dilaton
    Jul 3, 2013 at 17:44
  • 5
    $\begingroup$ Reopening questions the way people at Math SE do, has in my opinion the additional advantage that people who have less than 3000 rep and therefore not yeat access to the Reopen queue can take part in the reopen process by upvoting the answers of this post, which makes reopening of questions that deserve it more efficient. $\endgroup$
    – Dilaton
    Jul 3, 2013 at 17:54

112 Answers 112

0
$\begingroup$

[REOPENED]

The question on Contraction mapping principle was recently closed, but it is not a clear case of off-topic question. I thought it would be good to bring it up here for consideration.

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1
  • 2
    $\begingroup$ Perhaps not clearly off-topic, but it does look like a peculiar question to me. I am guessing OP saw the stated theorem ("Th.") in a book or paper somewhere and wants to know what it's good for. It would help to know what book or paper it was, so that some needed context could be divined. $\endgroup$
    – Todd Trimble Mod
    Nov 4, 2013 at 14:30
0
$\begingroup$

[Deleted by the OP]

I wonder if we were too quick to close https://mathoverflow.net/questions/137103/proving-finite-representation-of-integers-in-irrational-bases --- from one of the comments, it appears that this may be research-level mathematics.

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5
  • $\begingroup$ Certainly I was hasty, but my goat was got somewhat by "phinary" and "Cantor dust"; also @ARupinski's comment seems to suggest insufficient thought put in by the OP. $\endgroup$
    – Yemon Choi
    Jul 19, 2013 at 0:00
  • $\begingroup$ @Yemon, certainly some cases are easy, and there was no indication OP had thought through them. But it looks like there is some meat on that bone. $\endgroup$ Jul 19, 2013 at 0:20
  • $\begingroup$ I made the comment referred to above. As in a further comment I made on the original question, I think the question should be made more precise before reopening. $\endgroup$
    – user25199
    Jul 23, 2013 at 8:31
  • $\begingroup$ Also, more generally, is it worth making a comment or edit to original questions to alert people to the discussion here? $\endgroup$
    – user25199
    Jul 23, 2013 at 8:43
  • 1
    $\begingroup$ @Carl, I've added a comment to the question (although it will only alert people who look at the question). $\endgroup$ Jul 23, 2013 at 8:47
0
$\begingroup$

[REOPENED]

I think the following question looks reasonable to me: Bussgang theorem for cyclostationary processes

It was closed as "unclear what you're asking". But with all due respect to those who voted to close, I don't think most of them are very familiar with cyclo-stationary processes - I could easily imagine the question being completely clear and unambiguous to someone actually working in this area.

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0
$\begingroup$

I fixed the question Hom-set with functions and arguments as requested to be self contained and clear.

( I asked the question very late last night and only was able to fix it this morning in the UK. )

UPDATE: The question never got reopened, and has since been deleted.

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2
  • $\begingroup$ Dear Henry, I undeleted your question but it is up to the community to reopen it. $\endgroup$ Aug 31, 2015 at 23:24
  • 1
    $\begingroup$ Re-deleted 1 September 2015. $\endgroup$ Oct 8, 2015 at 22:27
0
$\begingroup$

Mathematicians who were late learners?-list

Reason: How is this no longer relevant or specific to a certain geographical area or time? It is a valid history question. That can't be specific to a certain geographical area or time. I think this is a very interesting question; likely to help, or at least interest other users. Therefore think it makes no sense for this question to be closed, so I request it to be reopened.

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0
$\begingroup$

[UNDELETED] (and upvoted to prevent redeletion)

This question does not seem unreasonable to me, and did not attract any votes or comments before it was auto-deleted. Perhaps it simply did not catch people's attention?

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1
  • 1
    $\begingroup$ I voted to undelete on the general principle that questions with no downvotes and which were not closed should not be auto-deleted. If a third person votes to undelete, they should perhaps vote the question up or the same thing will happen again. $\endgroup$
    – Lucia
    Nov 23, 2015 at 15:04
0
$\begingroup$

[REOPENED]

I'd like to reopen When does $\nabla\times(\nabla\times F)=0$ imply $\nabla \times F=0$ . It is a clearly stated question, and seems like it has some interesting connections to differential topology.

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0
$\begingroup$

[REOPENED]

{as of Mon Apr 11 15:03:06 UTC 2016}

The CW question Examples of math hoaxes/interesting jokes published on April Fool's day? was posted on 2016-04-01.

It has score of 69, 43 favorites and was answered by moderator.

I think it is too young to die and probably will edit, suggesting not to promote it to active on purpose.

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0
$\begingroup$

[REOPENED]

I feel that the decision about closing my question:

    Euclid vs Eratosthenes

was arbitrary. I hope that it will be reopened.

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0
$\begingroup$

[Re-opened] then [Re-closed]

Request to reopen Linear systems of equations with singular coefficient matrix.

This question has been mostly rewritten and has now 4 reopen votes, besides two answers.

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0
$\begingroup$

[REOPENED]

The question product distinct prime factors of prime(n)-1 and prime(n)+1 has been closed as "unclear". I edited in a suggested clarification, and OP has indicated that my edit conveys OP's intentions. Please consider voting to reopen.

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0
$\begingroup$

[REOPENED]

I nominate this question because it is not clear to me why it should be off-topic.

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0
$\begingroup$

The OP of Comparison of the classical Fourier transform and the Fourier-Mukai transform made an edit two days ago to add more focus to the question, and requests reconsideration. There are currently two votes to reopen the question, but since it has fallen off the front page, other users might not have noticed.

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0
$\begingroup$

[UNDELETED]

This question Order statistic of Markov chain sample path and related probabilities

which was auto-deleted due to lack of activity or votes, seems reasonable to me. But I am not a probabilist; comments from those who are would be welcome

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  • $\begingroup$ It's in danger of getting auto-deleted again, if it doesn't get some upvotes – isn't that right? $\endgroup$ Mar 16, 2017 at 3:47
  • 1
    $\begingroup$ @GerryMyerson I think one upvote is sufficient, but I'm not sure $\endgroup$
    – Yemon Choi
    Mar 16, 2017 at 13:21
0
$\begingroup$

[DELETED]

I think that between the editing and the comments this question has been clarified and can be reopened.

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6
  • $\begingroup$ You think the question should be reopened, but doesn't deserve an upvote? -- I think it seems a bit weird to vote to reopen a question with no upvote, but 4 downvotes ... . $\endgroup$
    – Stefan Kohl Mod
    Feb 9, 2017 at 14:16
  • 2
    $\begingroup$ @Stefan, I'm sure the downvotes came before the editing. $\endgroup$ Feb 9, 2017 at 21:46
  • $\begingroup$ Have voted to reopen $\endgroup$
    – Yemon Choi
    Mar 15, 2017 at 16:04
  • $\begingroup$ @Yemon, the question was deleted some weeks ago. I imagine it has to be undeleted before it can be reopened. $\endgroup$ Mar 15, 2017 at 22:40
  • 1
    $\begingroup$ @GerryMyerson: now undeleted $\endgroup$
    – Yemon Choi
    Mar 16, 2017 at 2:19
  • 4
    $\begingroup$ @GerryMyerson Meanwhile the question has been autodeleted again since it is still closed and has non-positive score. To resurrect the question, it would take 3 undelete votes, 3 more reopen votes and either 5 upvotes (to reach score 1) or an answer, in order to permanently prevent it from being autodeleted again. $\endgroup$
    – Stefan Kohl Mod
    Mar 18, 2017 at 20:42
0
$\begingroup$

[REOPENED]

Graduate-level reference on temporal point processes seems like a perfectly reasonable / . The topic is research level but could be introduced in an advanced graduate text or monograph.

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0
$\begingroup$

[REOPENED]

I originally voted to close this question. I've since reconsidered, and I've voted to reopen.

Basically, there are easy counterexamples for infinitely generated modules, slightly more sophisticated counterexamples for finitely generated but not finitely presented modules, and a positive answer for finitely presented modules. In comments, knowledgeable people have made false claims, so I think it's probably close enough to "research level" to reopen.

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0
$\begingroup$

[UNDELETED and then REOPENED]

The question Checking concavity of a highly non linear function

seems to have been closed over-hastily. Those with sufficient rep can see fedja's comments, and I am prepared to believe quite readily that if fedja thinks it is non-trivial, it is non-trivial.

I would like to nominate this for re-opening.

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1
  • $\begingroup$ How does this work – can a deleted question be reopened without first being undeleted? or does reopening automatically accomplish undeleting? $\endgroup$ Jul 28, 2017 at 4:57
0
$\begingroup$

[REOPENED]

A game-theoretical question in a political economy model is a well-written math question coming from research in a field outside of mathematics. It may well be easy but I think overall it would be worthwhile to reward the author with an answer.

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2
  • 1
    $\begingroup$ You're right -- the question is vastly improved from its initial formulation. I voted to reopen. $\endgroup$
    – Lucia
    Sep 21, 2017 at 23:00
  • $\begingroup$ Looking at the timeline I see that this question went through the reopen review with 3 votes to leave closed. However, it seems that some of the edits were made after the reviewers' votes. (Probably the OP is unaware that it is the first edit that pushes the question into the reopen review queue. Although I am not sure whether it made much difference in this specific case.) $\endgroup$ Sep 22, 2017 at 9:58
0
$\begingroup$

[REOPENED]

The question Why there exists a non-split sequence with the condition that $pdM=\infty$ was originally posted with unexplained hypotheses and notation, and I voted to close and left a comment. The OP has edited the question and it now seems basically fine. I've voted to reopen

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0
$\begingroup$

[Undeleted]

Could I request that Question 290941, "Is the Normal centralizer problem in P?" be undeleted? It is a sensible question, and I spent some time finding a reference for the answer. It was then deleted by the poster - I have no idea why.

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1
0
$\begingroup$

[UNDELETED AND REOPENED]

Can finite binary self-distributive algebras fit into small $n$-ary self-distributive algebras?

Can finite binary self-distributive algebras fit into small n -ary self-distributive algebras?

This question was deleted because it got no upvotes. A possible reason that the question did not get any upvotes is that it necessarily requires $n$-ary fundamental operations for $n>2$ and mathematicians typically do not work with ternary or $n$-ary fundamental operations See this question for possible explanations and for a discussion of ternary operations. Another possible reason it did not gain any upvotes is that the notion of $n$-ary self-distributivity has barely been studied.

Here are some reasons why the question and notions behind the question are reasonable.

  1. The notion of $n$-ary self-distributivity generalizes the notion of an “inner endomorphism” to a more general context. I have encountered $n$-ary self-distributivity in my encounters with ternary and $n$-ary Laver tables (ternary Laver tables are really cool).

  2. While the notion of $n$-ary self-distributivity may seem a bit difficult to investigate, the hull of an $n$-ary self-distributive algebra allows one to use binary self-distributivity to study $n$-ary self-distributivity. Since binary self-distributivity is easier to grapple with than $n$-ary self-distributivity, one should always take the hull of an $n$-ary self-distributive algebra.

  3. This question is one of the more basic questions one can ask about the hull of $n$-ary self-distributive algebras and about the nature of $n$-ary self-distributivity.

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2
  • $\begingroup$ Now, someone has cast an unexplained and unjustified downvote against this question. I have been getting many such unjustified downvotes for some time now. $\endgroup$ Mar 31, 2019 at 2:44
  • $\begingroup$ Now that I think about it, a 50 point bounty would have probably prevented such a question from being deleted in the first place. $\endgroup$ Apr 17, 2019 at 0:26
0
$\begingroup$

[UN DELETED AND REOPENED]

Is the variety of ternary self-distributive algebras generated by its finite members?

Is the variety of ternary self-distributive algebras generated by its finite members?

To convince you that this is a good question, let me explain a little about the mathematics behind this question.

Richard Laver has constructed a sequence $(A_{n})_{n\in\omega}$ of finite self-distributive algebras (which I now call the classical Laver tables), and he has shown under the existence of very large cardinals that the free self-distributive algebra on one generator embeds into $\varprojlim_{n\in\omega}A_{n}$. In particular, the free self-distributive algebra on one generator is contained in the variety generated by the classical Laver tables.

So I have extended the notion of the classical Laver table to a wide class of structures including the multigenic Laver tables. Furthermore, I have shown under strong large cardinal hypotheses that the free self-distributive algebra on countably many generators embeds into an inverse limit of multigenic Laver tables (the multigenic Laver tables are like the classical Laver tables but with multiple generators). In particular, the multigenic Laver tables generate the variety of all self-distributive algebras.

Now, the notion of self-distributivity can be generalized to $n$-ary self-distributivity and these generalized notions of self-distributivity give one an abstract notion of what it means for an algebraic structure to have “inner endomorphisms.” The notion of a Laver table can also be generalized to the notion of a ternary and $n$-ary Laver table. The only problem is that while the classical and multigenic Laver tables are always locally finite, the ternary Laver tables are in general not locally finite. The variety of ternary self-distributive algebras is probably generated by the ternary Laver tables, but since the ternary Laver tables are not locally finite, it is hard for me to predict whether the variety of self-distributive algebras is generated by its finite members.

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0
$\begingroup$

[DELETED, Undeleted]

Reversible varieties

In this question I asked about reversible varieties, and it seems like the question has been deleted unfairly. The question has 2 unexplained and unjustified downvotes and only 1 upvote, so it automatically got deleted. I do not believe that these downvotes have any legitimacy since I have recently been receiving many downvotes and all of these downvotes for the questions that I have asked are without any explanation.

In this question, I proposed the notion of a reversible variety since I noticed that several varieties including the varieties of groups, racks, quandles, and other varieties have a flavor of reversibility in the sense that the fundamental operations are simply projections of bijective functions which are composed of these fundamental operations. I think of the notion of a reversible variety as being a generalization of the notion of a group. I therefore wanted to know if this notion has been investigated before in the concept of universal algebra, and I also want to see more interesting examples of reversible varieties.

This question so far does not have much to do with reversible computation, and the motivation for this question did not arise from reversible computation.

Incidentally, this follow-up question (Is this condition sufficient for a variety to be reversible?) which is also about reversible varieties has not been downvoted nor upvoted (and hence not yet deleted).

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7
  • $\begingroup$ People are misusing meta in order to cast more unjustified downvotes to questions related to the deleted questions. $\endgroup$ Apr 17, 2019 at 2:55
  • $\begingroup$ Is there any reason why this post has a downvote? $\endgroup$ Apr 17, 2019 at 3:46
  • $\begingroup$ The MO community has recently made it exceedingly clear that they do not want me on this site. $\endgroup$ Apr 17, 2019 at 3:52
  • 4
    $\begingroup$ I see one downvote. ONE! A downvote doesn't mean someone doesn't want you here. I know you're not interested in my advice, but youtube.com/watch?v=SJUhlRoBL8M $\endgroup$ Apr 17, 2019 at 8:56
  • 4
    $\begingroup$ Oh, and, for the 17th time, if you feel you're being targeted with downvotes, please, please flag for moderator attention. Complaining here is pointless, as only a moderator can do anything about such a situation. $\endgroup$ Apr 17, 2019 at 9:02
  • $\begingroup$ Question has been undeleted BUT unless it sees some action (answers, upvotes) it will sooner or later be robo-deleted again. $\endgroup$ Apr 17, 2019 at 9:07
  • $\begingroup$ I have been flagging these sorts of posts for unjustified downvotes. In my recent experience, such flags have been declined. $\endgroup$ Apr 19, 2019 at 23:50
0
$\begingroup$

[REOPENED]

The closure of this question seems rather rude to me, in particular in view of the strong gender bias on this site. -- Also I think neither its vote score nor that of its five upvoted answers supports the claim that it is considered off-topic on this site. Therefore I suggest to reopen that question.

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3
  • $\begingroup$ Note that the vote scores have been inflated by the fact that the question became a HNQ, so they do not necessarily reflect opinions of regular participants of MO. $\endgroup$ Jul 11, 2019 at 14:31
  • 4
    $\begingroup$ Also, it is off topic, as its connection to mathematics is by circumstance, not design. If it were happening in a different field, say biologists venturing into mathematics, I don't think it would stand at all as on topic for this forum. I am willing to consider it an exception to the rules and leave it for inclusion. Its popularity does not make it on topic. Gerhard "Will Not Vote To Delete" Paseman, 2019.07.11. $\endgroup$ Jul 11, 2019 at 16:11
  • 2
    $\begingroup$ FWIW I have cast a 5th vote to reopen $\endgroup$
    – Yemon Choi
    Jul 13, 2019 at 6:54
0
$\begingroup$

[No response from the OP, so I will leave this lie. I'm not that keen that I'm going to chase it up]

The question How to sort differential equation list? seems to me to be not uninteresting. The original asked about how to sort a list of DEs in Maple, but it's not really the Maple content that the asker is interested in, but rather if there is some reasonable ordering on (a class of) differential equations such that given a collection of them one could sort it into a list, so as to compare with other resources like OEIS.

It still very badly worded, but the above is what I think the OP wanted to ask.

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3
  • $\begingroup$ I'd rather see OP rewrite the question so it's actually comprehensible. Perhaps by explaining it to someone who is fluent in Emglish, math, and whatever language is native for OP. $\endgroup$ Jul 20, 2019 at 12:20
  • 1
    $\begingroup$ Yes, I agree. This is more of a preliminary notice. I was going to encourage the OP to explain it more clearly. $\endgroup$
    – David Roberts Mod
    Jul 20, 2019 at 23:37
  • $\begingroup$ Given the terrible language, it’s not even clear to me if the question is really about differential equations, or if it’s just a mangled form of different. $\endgroup$ Jul 21, 2019 at 8:40
0
$\begingroup$

[UNDELETED]

I would like to add as undelete-request On variants of the abc conjecture in terms of Lehmer means that was automatically deleted yesterday. If possible, I think that it is an interesting question about the abc conjecture. Many thanks.

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10
  • $\begingroup$ I note that you haven't enacted any of my suggestions for making the question more attractive to other users. $\endgroup$ Mar 1, 2020 at 4:26
  • $\begingroup$ I don't know if you've read my comment adressed to you (in the Meta post now deleted), that I can not edit my question since it is deleted. When I thy to edit the post, this message is communicated "This post has been deleted - no more edits are allowed." Many thanks in any case @GerryMyerson and good weekend $\endgroup$
    – user142929
    Mar 1, 2020 at 8:13
  • 3
    $\begingroup$ @user142929 That seems some a bug which was also reported here: “This post has been deleted - no more edits are allowed” when editing own Roomba'd question. (Some possible workarounds are mentioned there, but it would definitely be better if the bug was fixed.) $\endgroup$ Mar 1, 2020 at 8:25
  • $\begingroup$ Mnay thanks @MartinSleziak $\endgroup$
    – user142929
    Mar 1, 2020 at 8:31
  • 1
    $\begingroup$ Sorry, I missed your comment on meta.mathoverflow.net/questions/4462/… (and why did you delete that question?). $\endgroup$ Mar 1, 2020 at 8:56
  • $\begingroup$ You do not have to apologize about you missed the comment. I' ve deleted my Meta post since I want to solve my problem: which is about of a question that I consider interesting and important was automatically deleted @GerryMyerson . I don't know if ask a post for a discussion in Meta of these sites is useful, let's say that I've lost part of my hope in the discussions of the Meta of these sites, and that the first thing is solve my problem. $\endgroup$
    – user142929
    Mar 1, 2020 at 9:12
  • $\begingroup$ Now it's undeleted, you should be able to edit your post. $\endgroup$
    – YCor
    Mar 1, 2020 at 17:01
  • $\begingroup$ Many thanks/Muchas gracias I've edited it while it was deleted, I can't make more substantial improvements following the professor's advices (see previous linked Meta, my previous recently deleted post in Meta) in this post, similar that those that I edited while it was deleted, but my purpose is to moderate/modulate myself posts following the advices, in particular I will try show my effort and more motivation in next posts @YCor . Sure that my post is interesting and after this stumbling block we can solve it $\endgroup$
    – user142929
    Mar 1, 2020 at 18:34
  • $\begingroup$ If the question doesn't attract some upvotes and/or answers, presumably it will be auto-deleted again. $\endgroup$ Mar 3, 2020 at 4:34
  • $\begingroup$ Many thanks for the information, someone upvote it, and I hope that some user do some attempt to solve it. My motivation is my feeling that can be an interesting post: I would not have insisted if the deleted post had been another of my posts (other unanswered post that maybe isn't interesting). Many thanks again to you and professors that vote undeleted the question @GerryMyerson $\endgroup$
    – user142929
    Mar 3, 2020 at 11:12
0
$\begingroup$

Status [UNDELETED] . (Thank you!)

I ask that Counting multiples in short intervals be recovered. I will provide an answer that is an enhancement of Lucia's comment as well as motivation for the question. It is part of my exploration of a combinatorial approach in number theory. (GRP20200411)

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3
  • $\begingroup$ "be recovered"? $\endgroup$ Apr 11, 2020 at 22:59
  • 1
    $\begingroup$ If it were voted into deletion by members, I might say undeleted. Instead, an algorithm determined it be deleted, and I want it recovered. Thank you for interest and help. Gerhard "Now To Take Some Steps" Paseman, 2020.04.11. $\endgroup$ Apr 11, 2020 at 23:19
  • $\begingroup$ OK, well, it seems to be there now. $\endgroup$ Apr 11, 2020 at 23:30
0
$\begingroup$

[REOPENED]

The question $2$-norm of idempotent matrix was closed, but I didn't think the answer was obvious, although an answer has been provided via a link in a comment. I think that comment could be left as an answer, so I have voted to reopen.

It also seems to me that some people who voted to close, and some who left comments, interpreted $\Vert \cdot\Vert_2$ as meaning the Hilbert--Schmidt norm whereas I think it is meant to be the operator norm. (Considering diagonal $3\times 3$ matrices shows that the result is false for any Schatten p-norm with $p<\infty$.)

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0
$\begingroup$

[REOPENED]

Reopening request for the question "Potency set" for power set

An edit to explain that the question asks for a reference was included, and the tag reference was added.

Moreover, another edit explains that it is relevant that for historical reasons, "power set" is an English translation of the German "Potenzmenge", which is still in use in German mathematical literature.

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