Requests for Reopen & Undeletion Votes, etc. (volume 10/2012 - 12/2014) [duplicate]

Question

The purpose of this thread is to help focus the attention of the community on posts that may require exceptional handling. This includes requests for reopen and undeletion votes. A request should be posted as an answer below.

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 linked thread. The goal is to keep this meta thread free of tension, so that everyone feels comfortable posting here. Please be polite, and respect the many different viewpoints in our diverse community.

To inform readers of the current (and past) states of the targeted post, please append tags such [REOPENED,RECLOSED] or [UNDELETED] at the start of the answer.

Beware that "short" requests such as "request reopening of <link>" may be automatically converted to comments by the SE software, so you may need to write more (e.g. why you think that the question should be reopened or undeleted).

Answer 1

[REOPENED]

I would like to request Motivation for the Tensor Product be reopened as I do not think it is a duplicate of and Motivation for Tensor Product.

The latter question asks "We already have Direct Product, Semi-direct products, so after all why do we need Tensor Product?", which is a question about why multilinearity is in general useful.

The former question (which was closed as a duplicate) asks "What's the reason/motivation to define the tensor product using the free vector space and that quotient to impose linearity? Can someone point me out the motivation for that definition?". These are questions about the specific construction of the tensor prodct, and NOT the general usefulness of multilinearity properties.

Answer 2

[UNDELETED]

Request for undeletion, or explanation of deletion:

https://math.stackexchange.com/a/898051/, a "hint" answer that does substantial work toward solving the differential equation in the question Differential equation $\sin \theta \frac{dr}{d \theta}+r\cos \theta =\tan \theta,0<\theta<\pi/2$. The answer received comments that it should be a comment, but I disagree. Substantial contributions toward solving the problem are often fine as answers, even if they do not go through the full details of a write-up of a solution. (Comments included a nonsensical one selected from a review queue.) It might be relevant that the answer was posted before the other, more detailed ones.

A moderator deleted it, so regular users cannot vote to undelete. I'm requesting that a moderator undelete it, and would be interested in explanations of why people think such an answer should be deleted.

Answer 3

[REOPENED]

(Also, as pointed out by Asaf in a comment below, this was a duplicate request. My apologies for the inadvertent dupliaction.)

---

The question "If every convergent subsequence converges to a then so does the original sequence" should be reopened (in my opinion).

It is a request for clarification/explanation of an argument from a text.

It was closed as off-topic since it is essentially a repost of an earlier, deleted question. The thing is: this earlier question was deleted by the Community User, hence cannot be reopened by 10K+ voters. My view is that the earlier question was reasonable as well; if it could be reopened, then I agree that the current version should be closed as a duplicate, and the earlier one revised for clarity and reopened. Since that doesn't seem to be possible, I have voted to reopen the current question, and I would ask others to do likewise.

---

In general, it seems a bit unreasonable to me that the OP has been put in a Catch-22, in which their current question is being closed essentially as a duplicate of an earlier question which is unable to be undeleted/reopened.

Answer 4

[REOPENED] Show that floating point $\sqrt{x \cdot x} \geq x$ for all long $x$.

I would like to see this question reopened. I believe it is a valid numerical analysis question.

Answer 5

I am trying to get

Let $G$ be a finite abelian group. Let $a\in G$ be an element of maximal order. Prove $|b|$ divides $|a|$ for all $b\in G$. A different proof

reopened. It was closed as a duplicate of Prove that for any element $b$, $|b|$ divides $|a|$ (order of $b$ divides order of $a$). and Finite abelian group generated by elements of maximal order. True the question has been answered, but I haven been given another outline of a proof for this and would really appreciate it if i could get some feedback on this version of the proof for this question

Answer 6

[REOPENED]

Is a line just an infinitely large circle? (formerly Whats wrong with this?)

I'll repeat the same thing here that I said in the comments:

To the closers and other downvoters, please consider that although it is stated in layman's terms, the idea behind it is a deep question about Moebius transformations / stereographic projection (or if you think I'm stretching, at least basic topology). In particular, even if you don't believe the question is stated well, it could inspire a very good answer. –

I fixed up the wording a little bit to help the OP come off less abrasive to mathematician sensibilities. (And changed the title.)

This is the type of question I would really like to see stay open on MSE: genuine curiosity about a mathematical intuition by a layman. Even if it looks little lazy on the surface, I think we need to encourage non-homework questions from non-mathematicians as much as possible.

Answer 7

[REOPENED] I would like this question:

https://math.stackexchange.com/questions/243115/field-extensions-of-cos-and-sin

to be reopened. The question was closed as a duplicate of Degree of field extension. Bit IMO, the questions are different. The closed one is about whether a specific proof is correct, not just a question about how to prove it (like the other question).

Answer 8

[Re-opened] I'd like to suggest reopening What is importance of the Bunyakovsky conjecture?. The question in the body, "how important do you consider the answer to this problem", may well be "too soft", but the question in the title seems to me to be a solid mathematical question.

Answer 9

[REOPENED] (Thanks.)

This question. I think that there may be insights that only working mathematicians could provide (as opposed to philosophers), and even if there are wildly differing points of view, seeing them described may be useful.

I understand that the question is not mathematical in the sense that "how do I integrate such-and-such" or "why is this number divisible by that one" are. I also believe its answers may be more interesting and useful in the long run.

Of course, it may be that answering the question in detail, considering as many of its subtleties as possible would just be too long and unfeasible. That's fine; even providing a few references and ideas that can potentially be fleshed out would be more useful that simply dismissing it.

Related.

Answer 10

[REOPENED] This question should be re-opened as the OP has edited the post to try to tell us what they have done.

Answer 11

[REOPENED] Thank you.

The question was undeleted by the OP, and has now been closed. I think it does more good being open and have myself voted to reopen. As I told the OP elsewhere, "The thing is, many (oh so many!) people think that mathematics is just about computations (long and tedious and often times pointless). And many among those that know better think that the only way to use a computer is to help with these computations. But there is much more to math than that, and many more uses of a computer in mathematical research. And there are the incompleteness theorems, showing that not all mathematical practice can be automated anyway. Good answers to your question could be quite insightful!"

---

This question was actually deleted, but I think it is interesting and can be useful to many, not just the OP: Why are there mathematicians that do not use computers?

I was watching a video on Andrew Wiles and his proof of Fermat's Last Theorem and I quite liked the video, especially the complexity of the proof only to prove a simple concept which can be understood by most people. I also liked the graphics they used to illustrate elliptic curves and modular forms.

But then Andrew Wiles said that he never uses a computer, he only uses pen and paper and I also heard of other mathematicians that don't use computers.

Do they not use computers because there are problems only a mathematicians can solve or are there other motives? Wouldn't the proof have taken much less than 7+ years if he used a computer?

I have voted to undelete. I am posting this request here as it seems a natural extension of the intention of this post. Also, if there are issues with the question, this may be the place to address them, which may also prove useful on its own.

Answer 12

I think that the

1+1+1+1 ...= -1/2

question, which at present is a merger of an older 1 upvote/1 (not so highly voted) answer Math SE question and a two days ago migrated from from Physics 5 upvotes/highly upvoted answers question, should be reopend as there is IMHO nothing unclear about the OP asking for an (intuitively understandable) proof that $ 1 + 1 + 1 + 1 \cdots = -\frac{1}{2}$.

Answer 13

[REOPENED]

The question Is there a highest order of infinity? was closed as a duplicate. Its original version asked whether "there is a limit to the orders of infinity", something that has been asked here several times already. The person asking the question has since clarified that what they are asking for is something very different,

Does there exist an infinite set of cardinality such that it can never be reached by taking power sets of a set with cardinality aleph-null?

(By the way, if reopened, an answer may as well clarify that $\beth_{\omega}$ is far from being "highest" among the infinite cardinalities.)

Answer 14

[REOPENED]

I do not agree with the closure of this question.

While the user does not have enough mathematical sophistication himself to formulate the question as one in analytic geometry, the description of the problem is clearly one of mathematics. So I don't see how it can be closed as off-topic. (I would vote to re-open myself if it weren't for my binding mod powers.)

Furthermore, it appears that the user encountered the problem in a real-life scenario and so he provided context.

The fact that the question does admit a simple mathematical answer should not be held against the original asker: we were all ignorant once.

Answer 15

[REOPENED]

This question was closed as a duplicate of this question. But it's not a duplicate. The limits of integration are different.

Answer 16

[REOPENED] The question How to define a well-order on $\mathbb R$? were closed recently due to the confusing nature of the word "define".

If by "define" we wish to mean "explicitly describe without any appeal to the axiom of choice" then it is indeed a duplicate. However as the comments clarify, this is not the case.

I believe, if so, that it is not a duplicate of the question it was closed as a duplicate of (or any of the questions in the links in the comments I posted, as well).

---

Thank you Andres Caicedo, rschwieb, Belgi, Matt Pressland.

Answer 17

[REOPENED] I would like to see the question on "mathematics in the movies" reopened. It asks about feature films depicting math, and/or mathematicians. I think it is at least as relevant to math, and this site, as are many other "soft questions" that still stand as open. After all, we DO have tags "math history", "education", "big-list", etc.. If questions relevant to those tags are thereby subject to closure, then the tags should be removed from this site; else, they are appropriate topics on which to post.

If reopened, I think it might very well be appropriate to "wikify" the post (community wiki), but this question has merit.

---

ADDED, to answer Marvis's comment below: This post is not a "strict subset" of the post to which Marvis provides a link. They are sufficiently different posts to warrant separate consideration. (See for example, Rahul's reply to Marvis).

Answer 18

[MIGRATED] I would like to see https://math.stackexchange.com/questions/256079 reopened.

• The stated reason for the closure ("not constructive") does not apply. There were answers, and they were supported by facts. The question did not solicit debate or arguments. There was a meta-debate, but it was about the appropriateness of the question, not its content; considering such a debate as a reason for closure would be circular, as one could then get questions closed simply by starting a debate on whether they should be closed. Nor is there any reason to expect that the question will solicit debate or arguments in the future. The question does fit our Q&A format; a question was posed and answers were given; that the answers were of the form "the question can't be answered because there's not enough information" is quite a common occurrence and not a reason for closure.
• The stated reason for the closure bears no relationship to the reasons for closure given in the comments. The reasons given in the comment are not valid reasons for closure. Personal opinions on whether the OP should or shouldn't try to assess the chances of his wife having a serious disease by asking a question on a math Q&A site shouldn't enter into the decision whether this question is suitable for this site. It's the OP's decision and not ours whether he wants to ask this question here.
• There were two answers at the time of closure, which had several upvotes and contained information potentially valuable to the OP. Even those who commented on problematic aspects of asking such a question on such a site can hopefully agree that it's good if the OP knows that there's not enough information in his question to answer the question.
• I don't know the current status of the close vote cancelling policy proposal; it may or may not be relevant that I cast a no-close vote in a comment, no-one cancelled it and it received three upvotes.

Answer 19

[RECLOSED] https://math.stackexchange.com/questions/327695/how-are-arrays-defined-with-gap

I really hope we can get past this anti-computer attitude. If you don't want to do computational mathematics, that's fine, but please don't obstruct the participants who do. Just ignore the tags if you don't like the questions.

"We welcome questions about: ... Software that mathematicians use" - FAQ.

It's a reasonable question and the current answer lists only one way to create arrays in GAP. There is still more to be learned.

---

For the same reason, I voted these to be reopened:

https://math.stackexchange.com/questions/209266/how-do-i-break-magma

and

[REOPENED] How does the function CycleIndex work in GAP? ( undocumented in GAP )

Answer 20

[REOPENED] Find $\det X$ if $8GX=XX^T$ was closed as not a real question. I have edited it in light of comments by OP. I think it's a real question now (albeit an easy one, that I have answered in the comments).

Answer 21

[REOPENED] What explains this bizarre behavior?

I would like to see this question reopened. I believe it is a valid dynamical system question.

Answer 22

[REOPENED] (Thanks!)

I would like to see this question reopened.

In fact, I do not understand why it was closed to begin with: The OP posted the question, and illustrated with examples what they meant. The question does not appear trivial, and its formulation takes some preliminaries, so it cannot just be stated in two lines.

In case the question is not clear, let me rephrase it as I did in the comments (but really, looking at the examples the OP provides may be better than chasing through the formalism here):

Let $f,g$ be any linear functions from $\mathbb R$ to itself. If $h$ is a function obtained by composing $f,g$, in any order, say $h=j_1\circ j_2\circ\dots\circ j_n$, where each $j_i$ is $f$ or $g$; and $s=s_h$ is the fixed point of $h$, then we can associate a cycle to $h,s_h$ by considering the finite sequence $$ a_0=s_h,\quad a_1=j_n(s_h),\quad a_2=j_{n−1}\circ j_n(s_h),\dots,\quad a_n=j_1\circ \dots\circ j_n(s_h)=s_h. $$ (Note that the $a_i=a_i(h)$ depend on $h$.) Define $\mathrm{Sum}_g(h)$ as the sum of the $a_i$ with $i<n$ such that $j_{n−i}=g$.

Now, let $S$ be obtained by composing $f,g$ in any order, and let $T$ be the result of composing in the reverse order, so if $S=j_1\circ\dots\circ j_n$, then $T=j_n\circ\dots \circ j_1$. The question is: Is it true that we always have $\mathrm{Sum}_g(S)=\mathrm{Sum}_g(T)$? If so, how can we prove it?

Answer 23

[REOPENED] I have no doubt about what this question is asking and have actually posted an answer in the form of a pair of comments. I’d prefer to give it a ‘real’ answer, however. I note that the question already has three votes to reopen.

Answer 24

[REOPENED]

This question (A) was closed as a duplicate of this one (B), but question B has no answers and question A already had one on closing. Question A also had much more detail in the question itself.

I pointed out the first fact in the comments while close votes were being cast but it was closed anyway.

I think question A should be re-opened. It might be worth considering whether B should be closed as a duplicate of A as well.

Answer 25

I would like to request that the following question be re-opened.

Any two sets $Y$, $Z$ have the same cardinality $\iff$ there are injective functions $f: Y \rightarrow Z$ and $g: Z \rightarrow Y$.

I has been closed as a duplicate. However, it is a "check my proof" question and so cannot be a duplicate. Yes, the underlying maths problems are the same, but the actual questions being asked are not.

Answer 26

[REOPENED]

The question Is there a continuous bijection between an interval and a square: $[0,1] \mapsto [0,1] \times [0,1]$? was closed as a duplicate of an older question A bijective function between a square and its side

In my opinion, the newer question is better formulated (for example, the title corresponds to the body of the question) and it has more answers. So I suggest to reopen this question and close the older one as a duplicate instead.

(I have suggested this in the comments and in chat before the question was closed. This might be the reason that the older question has already received two closed votes. However, now that the newer one is already closed, it cannot be chosen as a target for closure of the older question as it would cause circular duplicate links.)

EDIT: Since the newer question is already reopened, the older one can now be closed as a duplicate.

Edit 2 (LF): Older question is closed.

Answer 27

[REOPENED]

A formula for the power sums: $1^n+2^n+\dotsc +k^n=\,$? , from a user investigating that sum, presents a method that the OP tried to get the sum in closed form, observes that it doesn't work well, and then asks “are there other ways?”

The purportedly "duplicate" question Finite Sum of Power? also asks for the closed form, but not for a derivation, or for techniques to approach the problem, and the answer there doesn't give any.

(I voted to close the question, and on reflection, I regret my vote. I have voted to reopen it. I will try to be more careful in the future.)

Answer 28

Please reopen https://math.stackexchange.com/questions/692746/intuition-if-f-differentiable-and-lim-x-to0-fx-l-then-f0-l

This question is for intuition only and no proofs. The other is for proofs. Ergo they aren't duplicates. The closers left no comments?

Answer 29

[REOPENED]

I think this post should be reopened: Evaluate $\int\frac{\sqrt {25 - x^2}}{ x^4}$ (It already has 4 reopen votes, so only one vote is missing.)

It was closed as a duplicate of another post, but they are definitely not duplicates. (It seems that the problem might have been that the OP did not know how to make a post using TeX/MathJax.)

If course, if there is indeed a duplicate somewhere on the site or if you think that it should be closed for another reason, I do not object to closing the question. But at the moment it is closed for incorrect reasons.

Answer 30

[REOPENED]

My question here was said to be too broad, so I tried to edit it with a more specific example: How can you tell when you need to use the binomial coefficient for probabilities?