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).

Note: Many moderators do not wish to cast their binding reopen vote till it is the final fifth vote needed. To help moderators participate optimally, the following scheme may work. Moderators may add comments indicating their desire to cast a reopen vote. If someone notices that there are enough mod votes to bring the reopen tally to 5, then please ping/flag a mod to reopen the question.

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@Bill: I saw no reason to wait with that idea. There was no actual discussion in this thread anyway. –  Asaf Karagila Oct 24 '12 at 18:34
@Asaf, I opted for cursing the darkness rather than lighting a candle. Anyway, the question has been reopened. –  Gerry Myerson Nov 9 '12 at 21:54
@Gerry: Darkness is just the light's way of proving the empty set exists. –  Asaf Karagila Nov 9 '12 at 21:55
@Willie: I think that we should delete old reopening requests and perhaps have one post/additional thread for indexing them. I should also think that any request older than $n$ days for some reasonable $n$ should be deleted. If something has not been reopened and the initial votes expired... well, it makes sense to conclude that there aren't that many people interested in reopening. –  Asaf Karagila Nov 30 '12 at 9:49
@Willie It's probably useful to have some nontrivial history remain so that folks $\rm < 10K$ can gain some idea about what types of questions do get reopened, and what types don't. By quickly scanning the requests it might help to convey some idea of the community consensus on marginal topics. To keep the unopened requests at the top of the active sort, they could easily be bumped if there is still interest. –  Gone Dec 1 '12 at 1:44
@Belgi: This is why I prefer to browse Meta with answers sorted by activity. –  Rahul Narain Jan 5 at 21:38
@Belgi Sorting by activity solves the problem. I just bumped the only active discussion to the top with an edit. There are two requests dated by November 2012, which I guess are no longer ongoing conversations (but anyone so inclined can bump them; it's a CW). –  user53153 Jan 5 at 22:07
Thanks for the workaround, I still think theres no reasons for this to log all reopen request that were/will be made –  Belgi Jan 5 at 22:10

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

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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.

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I think one thing that would help is if the two questions are edited to they have more precise and more distinct (from each other) titles. –  Willie Wong Mar 18 at 12:16

[REOPENED] I would like this question:

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).

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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

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[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.

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I cast the fifth and final vote. –  Willie Wong Mar 13 at 12:32

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

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[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.

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@Thomas That's fine. In this case, I believe the deletion happened because of the downvote, which I consider unwarranted. Regardless, I think (as I said) that the question can be useful to many, not just to the OP, which should (surely?) be our main consideration. –  Andres Caicedo Aug 11 at 19:23
I agree that the question with answers could be useful. But, on principal grounds, I believe that it is wrong to undelete a question that the OP him/herself deleted. I think a better approach is for someone else to repost the question. I don't think that we should assume we know why someone decides to delete his/her own question. –  Thomas Aug 12 at 2:42
Ok, I didn't know that. In that case I see no problem. –  Thomas Aug 12 at 12:45

[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.

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That depends on what your definition of is is. –  Graphth Oct 26 '12 at 15:57
@Graphth: The answer on that depends on what is your definition of definition. –  Asaf Karagila Oct 26 '12 at 15:58

[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).

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I would like the part about "what kind of stories would you like to see in the future" removed as it is discussiony and off-topic. I said that in my comment on the question, but the asker chose to ignore it and freak out instead. –  Rahul Narain Nov 22 '12 at 17:50
I believe that this question is a strict subset of math.stackexchange.com/questions/18843/… –  user17762 Nov 22 '12 at 20:28
@Marvis: It seems to me the questions are split along fiction/nonfiction lines. –  Rahul Narain Nov 22 '12 at 22:42
points to comment that has been ignored yet again –  Rahul Narain Nov 23 '12 at 20:10

[MIGRATED] I would like to see What are the chances my wife has lupus? 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.
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@Gerry: My main point is that this is for the OP to decide, not for us. It seems that you and others disagree (though I don't think any argument against that principle has been offered yet), so I'll argue on the merits even though I think we shouldn't: Many questions are life or death questions. If someone posts a question on how to optimize a process and save the government a lot of money, that money can be invested in better hospitals or safer roads instead; yet no-one would claim we shouldn't be giving mathematical advice on that optimization. –  joriki Dec 11 '12 at 12:51
This question is more directly related to life and death, about as directly as the present question. It has $150$ upvotes, no close votes and $17$ answers, one with $48$ upvotes. Should it be closed? If not, where is the difference? –  joriki Dec 11 '12 at 12:52
The question was migrated to stats.stackexchange.com/questions/45807/… For the moment, there is also my question stats.stackexchange.com/questions/45804/… with an excellent answer by an epidemiology guy, but the two questions will probably be folded together. –  Will Jagy Dec 13 '12 at 0:35
@joriki, I don't mind doing unpaid work to help people learn mathematics. I do mind doing unpaid work to help people in private money-making enterprises. If they are going to make, or save, some money out of it, they should be willing to pay someone to help them. –  Gerry Myerson Jan 6 at 15:19

[REOPENED] I would like to see this post reopened.

It is clear that it generated a lot of thought about relations, their properties, etc. Many questions of this nature are posted to this site, and are not closed as "non-constructive." Many students are very interested in "real-life" applications/interpretations of the math they are learning. ${}$

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I don't think this post should be re-opened, although I agree that "non-constructive" might be off-putting. I think that the question generated a lot of buzz, which is good, but when you have several repeated answers and deletions it's time to close down. If we had "no longer relevant" as a closing reason I would vote that. –  Asaf Karagila Jan 5 at 14:09

[REOPENED] Find $\det X$ if $X$ satisfies the equation $8GX=XX^T$ 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).

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[REOPENED] What explains this bizarre behavior?

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

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I voted to reopen. The OP noticed a very interesting effect that has puzzled a lot of people over the years. –  Grumpy Parsnip May 4 at 15:53
@Grumpy: More accurately, we noticed an interesting effect, and we are assuming the OP noticed what we noticed. (And admittedly, I did not notice, because my eyes glazed over at the wall of digits and I didn't see the signs, although I did track the pattern of the decimal point) –  Hurkyl May 5 at 1:01

[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.

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[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?

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[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.

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[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.

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[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.

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Sorry - I should have mentioned why I thought that. It was so that we could have a question which discussed this case and which could be used as precedent for future cases. Currently, the precedent is hidden away here and so isn't going to get the exposure needed for it to be a proper precedent. –  user1729 Oct 1 at 12:19
@user1729 There already is a post about this: Topics declared as duplicates in which order?. (Although there are no answers there and that post seems to me to be about a particular instance, not about a general principle.) Feel free to make a post on meta about this problem, if you think it is needed. (I think it might be better to discuss the general principle on meta rather than some particular case of this problem.) –  Martin Sleziak Oct 1 at 12:25

[REOPENED]

$1^n+2^n+\dots +k^n=$? , 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.)

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Will you please to appreciate the fact that most of the downvotes in its Meta thread (How to Adapt or Emend : Specific Advice/Tips to Streamline Studying Math) occurred before my edit to my question, and observe Lord_Farin's gracious comment underneath his answer thereunder.

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[REOPENED]

I would like this question reopened. Closing it because the OP didn't state anything beyond the bare question is a little harsh, and the question is interesting.

EDIT: Paul Siegel's answer has been accepted with 3 upvotes. That seems to indicate that reopening is appropriate.

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@Did: because closing it seems like a heavy-handed way to get the OP to respond. The detailed comment that was left was more than sufficient. –  Grumpy Parsnip Nov 3 at 22:22
@GrumpyParsnip Two weeks later... and in view of the subsequent (or lack of) events, do you still hold the same view? –  Did Nov 17 at 14:47
@Did: I still think it deserves to be reopened, even if it has been abandoned by the OP. It's the question itself that is interesting, not the person behind it. –  Grumpy Parsnip Nov 17 at 19:52

[REOPENED. I cast the binding fourth vote on behalf of myself and Bill Dubuque]

This question: Prove $f(S \cap T) \subseteq f(S) \cap f(T)$ was voted to be closed as a duplicate of Is this a valid proof of $f(S \cap T) \subseteq f(S) \cap f(T)$?

However, the question asked actually was different. The latter asks for the readers to check whether the OP gave a valid proof (he didn't, and counterexamples were given as answers). The former asks for a proof. The closest answer we have on the latter to this question is this sketch of a proof. So I don't really think the two are exact duplicates of each other.

(The other proposed duplicate target is a mistake, as noted in the comments.)

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I agree, since your vote and mine bring the count to 5, you should feel welcome to reopen it. –  Gone Nov 6 '12 at 14:33

[REOPENED] I would like the following: is $0.\overline{99}$ the same as $\lim_{x \to 1} x$?

to be reopened. The question is currently closed as a duplicate of Does .99999... = 1?.

While I agree that at the base is indeed that $0.\overline{9}$ = 1, but the OP actually says that he/she knows the proof of this. It seems like the question is more about the confusion about the function that is introduced in the question. While the question might not be worded perfectly, I don't think that it should be closed.

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[REOPENED]The question A question about a series with a strange property? should be re-opened. As the OP remarked the supposed duplicate does not actually answer the question posed.

(More details: the supposed duplicate has two questions in it. One without sign restrictions. The other restricting to positive series. An answer was given and accepted for the latter. But no answer was given for the former. The new question explicitly asks for the former.)

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[REOPENED] This question about a set containing itself was closed as "not a real question", with both posted answers interpreting it as a tautology that $X \subseteq X$. However, the question is really about the paradox $X \in X$; the word contains can have another meaning as $\ni$, and the question actually mentions the axiom of regularity! Granted, it's not a great question, and is easily resolved by prodding the asker about the definition of set complement, but that doesn't make it "not a real question".

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[REOPENED] Please reopen From a mathematician's point of view, what is the purpose of '$dx$' in $\int f(x)\ dx$?. I had written out (what I thought of as) a nice answer, then just before trying to post it, it was closed as a duplicate of What is $dx$ in integration?.

However, this question is different since it deals with the difference in the way physicists and mathematicians understand $dx$ (something that my answer was going to address).

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[REOPENED] In this question, the OP has edited to point out why the question isn't a duplicate. Please reopen.

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[RECLOSED] 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:

How do I break MAGMA?

and

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[REOPENED] I would like to see How to prove the earning decomposition of 2 people in mediocristan and extremistan? reopened. Please note that a highly reputed user has added a comment saying: "I would like to reopen and answer."

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