Requests for Reopen & Undeletion Votes (volume 01/2021 - today)

The purpose of this thread is to 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 is closed pushes the question into the reopen review queue if the edit is done within 5 days of closure, and so does a reopen vote. (If the review has already been finished, it is shown on the timeline of the question.) When 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 the information Reopened or Undeleted at the start once the request has resulted in some action. (If the action is undone, add this too, like Reopened, Reclosed.)

• Do not only post a request, like "request reopening of link". 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 it in a way that takes the feedback the post received into account positively 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 CURED is a reasonable place for such requests. The same guidelines apply there.

Earlier versions of the thread that served as a model:

Undeleted

Please undelete Functional Analysis: Finding finite functions over different norms as the question asker self-deleted his/her own question one day after receiving an answer.

Undeleted

Please undelete Group theory question of red and blue blocks as the question asker has self-deleted his/her own question a few hours after receiving an answer from a trusted user.

• Trusted users should be trusted not to answer copy-paste homework questions. – Gerry Myerson Jan 26 at 3:46

Undeleted

https://math.stackexchange.com/a/3980921/43608

This is a deleted new answer to an old question (from february 2019), by a user that has been on MSE for 1 year and 10 months, but does not seem to have questions or answers yet.

The deleted answer is short, arguably too short, but would be at least a good hint in the correct direction (it was for me, when I tried to figure out whether to vote to delete or not in review queue).

The question is ambiguous, as noticed by the two answers already here, but I think the new one has the correct interpretation (that the coefficients $$a,b,c$$ are independent of $$n$$), since it leads easily to a unique solution, as expected.

I believe the deleted answer is correct while the two undeleted ones are not, and thus deserves to be undeleted.

• Looks to be undeleted now. – Teresa Lisbon Jan 12 at 5:53

Undeleted

Please undelete Given a $1 \times n$ board and $4$ colors including white,red,yellow,blue as the question asker has deleted his/her own question after receiving a well-written answer. That's not something we wish to see after spending effort on other's question.

• For future reference, "The asker deleted the question immediately after getting answers" is something that may be worth raising a flag over. – Xander Henderson Jan 25 at 23:00

Undeleted

An answer of mine to Resources, references, or examples for logics with finitely many sentences was deleted via review.

May I kindly ask to reconsider this deletion. My answer relates to the observation that finite problems are always trivial in the context of computational complexity (see, e.g., the accepted answer here). The OP requested some clarification under my post, and I would have gladly given this clarification but my answer was already deleted then.

EDIT: It seems that I could undelete the question myself and provide the clarification. Is this the recommended way to proceed?

EDIT: I took the liberty of undeleting myself.

Would it be possible to reopen: Counting how many items can be weight on a scale if we pick the weights optimally
It has an accepted answer and is not the same as the post that is linked to. Thank you for your time.

Re-opened.

Please reopen Less common probabilities and expected values related to the coupon collector problem. It is falsely closed as a duplicate. Though the question brought in the title is indeed very often it is not asked in the body of OP.

Particularly the question asks about the expected value of collected unique cards after a certain number of trials, not about the expected number of trials to collect a certain number of unique cards. Though the former question is probably have been already asked and answered here, it is certainly not that one which was linked as "original".

• What you say about not being a duplicate is true, but this is so because the OP asks multiple questions. By itself that is not a fatal flaw (the problems are closely related), but the Question provides no context. It appears to me to be a "pass through assignment". If you like the Question enough, perhaps leave a comment for the new user to provide context, or repost the problem with your own context. – hardmath Feb 10 at 16:46
• @hardmath OP indeed asks multiple questions. But none of the questions is asked or answered in the alleged "original". I would not complain if the question was closed because of "providing no context". This would stimulate the author to correct it. But the given link certainly will not help him or her to find the correct answers. – user Feb 10 at 16:52
• @hardmath That would be great. – user Feb 10 at 17:01
• After a bit of research I chose one of the coupon-collectors Questions that asks about the probability distribution aspect, and which not only has a decent Answer but also links to many other Questions of a similar nature. Of course the expected value problems are easier than working out the probability distributions (after $x$ cards bought), but the OP has done literally nothing to motivate writing out a new Answer. – hardmath Feb 10 at 23:57
• @hardmath The given link is of course very interesting but it does not address the asked questions, neither do the links inside. Though I agree that it can help to point out the direction (if the asker has a solid background). – user Feb 11 at 8:43

A Basic Limit From Exponentials

I believe this is not a duplicate of How does one prove that $e$ exists? which was why it was closed.

The question from the first link asks why the limit $$\ \displaystyle\lim_{x \to 0} \frac{2^x-1}{x}\$$ exists. Whereas the question from the second link asks to prove that there exists a number $$a$$ such that $$\ \displaystyle\lim_{h \to 0} \frac{a^h - 1}{h} = 1.$$

The magma-cas is 100% mathematical software, and questions about it are not usually answered when posted on Stack Overflow. While the question is about how the software handles caching, MSE is the place to post this where it will most likely get an answer (and it has an answer; there are better answers that could be posted if it was not closed). It is also not a low-quality question that can be answered by pointing to the documentation.

[Edit:] MSE is where to post about these programs (magma, sage, gap) to get answers. The takeaway from the meta post linked in the comments is that no other SE site has a dedicated tag for the Magma CAS- in fact posts there are likely to be confused for a different computational package with the same name. There is no online forum anywhere. These posts are of interest to mathematicians and mathematicians only.

• To give the counter-argument, questions about implementation are explicitly noted as off-topic in the Help Center: "Algorithm implementation/design, computer simulation and modelling, etc. [might better be asked on] Stack Overflow". – Xander Henderson Feb 13 at 19:54
• @XanderHenderson That is not for the magma computer algebra system, it is for a different sortware package that is also called magma (though it looks like there are maybe a few random questions for the computer algebra system in there by mistake; they are told they are in the wrong place). – Morgan Rodgers Feb 13 at 19:56
• I've revised my comment. Also, note that this has come up before: math.meta.stackexchange.com/questions/22052/… – Xander Henderson Feb 13 at 20:02
• Also relevant: math.meta.stackexchange.com/questions/17119/… (takeaway: "being software used by mathematicians, Magma questions are on-topic here.") – Morgan Rodgers Feb 20 at 20:16

Not sure if this belongs here, but Community accidentally deleted this question that I answered:

https://math.stackexchange.com/questions/3977648/how-can-i-find-the-mass-of-the-pencil-cylinder/3977750#3977750

(for +10k)

Does 'the binomial expansion of a negative prime number yield its equal and opposite trigonometric value'?