20

Please vote up if you agree that the requested undeleting is a reasonable (useful, beneficial) action for the community. Vote down otherwise.

17

[RE-OPENED and later CLOSED again]
The question How the idea of adjoint matrix has been designed? isn't great, but isn't awful, and these two answers have been posted (and upvoted) on G+ rather than as answers, which is dumb. Let's reopen the question so that the answers can be added.
As an aside, the fact that Allen Knutson basically said "this is going ...

10

[REOPENED]
Why was User retention rates on MathOverflow closed (on meta)? It's not a great question, I agree, but it's not exactly off-topic on meta to ask about user retention rates on the main site, and explanations for observed statistics.

8

[RE-OPENED]
I believe the post Can you write $\mathbb R^2$ as a disjoint union of two totally disconnected sets? has been closed (or put "on hold") erroneously, as a duplicate of Can you explicitly write $\mathbb{R}^2$ as a disjoint union of two totally path disconnected sets?
Certainly the question is different; note that the consensus to the first ...

8

[REOPENED]
I find nothing wrong with Linear Algebra Text Book. Certainly MO.1 entertained plenty of questions about pedagogy without any controversy, and the selection of a linear algebra book with a view toward proof and standards of rigor is a perennial issue for teachers of undergraduate mathematics.

7

[REOPENED]
The question A normal distribution inequality was originally phrased in a way that sounded like an exercise, and rapidly got downvoted and closed. I'm not a probabilist, bun in its current form it looks like it could be a genuine question worth re-opening.

7

I've undeleted this answer. (And also edited the link in the comment.)

6

[REOPENED]
Derek Holt, a highly respected researcher in group theory, wonders aloud why A subgroup intersects conjugacy class of every prime power order element was closed. I don't understand the closure or downvotes myself.

6

[REOPENED]
The OP of this question Connected sum is well-defined for surfaces, proof? requests reconsideration to reopen.
It was closed as a duplicate, but OP says that what is asked for was not answered at the other post; he/she wants a simple self-contained proof that doesn't invoke anything so powerful as the Annulus Theorem. OP believes that for the 2-...

5

[REOPENED]
An ideal candidate to get things started is this question, Preparing for set theory research. I am definitely not happy with the wording, but I understand it may be very useful for beginning graduate students, and so it probably deserves a shot.

5

[REOPENED]
I'd like to nominate this question. It originally got closed due to a typo, which has been fixed. It's certainly not "unclear what you are asking" any more (the original reason for closing), and it looks like a perfectly reasonable question to me.
I have a (rather quick) answer ready, and it's mildly frustrating not to be able to post it.

5

The question
A question on $p$-approximation property from 2014 has been automatically deleted owing to lack of upvotes. While I can't immediately tell if it is a good question, it seems a perfectly reasonable one, which is unlikely to attract bad or vague answers, and might eventually get a proper answer.
For those who have high enough rep to see the ...

5

[RE-OPENED]
I think that the question How does a mathematician choose on which problem to work? was too broad in its original formulation (beginning: "How does mathematical research work?") and so I have revised it in a way that I hope allows it, as a soft-question, to be (re)re-opened. It is certainly not intended as a finalized product; only a more ...

5

[REOPENED]
Parameterizing rotations of a cube
was asked and answered, but I don't see a reason for closing it.

5

[UNDELETED]
This is an undelete request for an answer on meta: namely, quid's answer to my question Some proposals for modifications of the process of closing/reopening questions . The answer was accepted, but yet got deleted when quid left the site. This was not quid's intent, and I also checked that quid was fine with the answer being undeleted (see ...

5

[REOPENED]
I'd like to suggest reopening Covering systems. As I wrote in a comment,
Why is this closed? Covering systems are a recognized area of research in Number Theory. It's known that in an irredundant cover with a modulus divisible by a prime $p$
there are at least $p$
moduli divisible by $p$. This asks whether, if there is a modulus divisible by ...

4

[REOPENED]
"Find a TSP tour passing through at least one node in each set of nodes" was initially unclear, but the author
has now clarified it into a real question (and I corrected the English):
Is there a PTAS (polynomial-time approximation scheme) for this problem?

4

The question How to find generators to Mordell weil groups of elliptic curves? was originally phrased in the narrow context of inquiring just about the software Sage. I had voted to close that, but the revised more general question seems worth reopening. I have cast my vote to reopen, but am not sure that the revised question has received enough attention. ...

4

[REOPENED]
I think this question:Are there infinitely many natural numbers not covered by one of these 7 polynomials? should be reopened. Please see the comments by me and Joel in main.

4

[REOPENED]
The question
Finding all local maximum points of a function?
does not seem as trivial to me as has been supposed. Sure, one can set the gradient equal to zero, but how does one actually prove that the only solutions are the "obvious ones"? At the very least it seems worth leaving the question open for a while.

4

[REOPENED]
I think people were pretty hasty in shutting down this question: Shape of axioms in abstract algebra. I could just barely squeeze in some highly relevant content and context in a comment before the thing was shut down. I request that this be reopened.

4

A couple of questions about Turing machines that are bounded in space but have an infinite amount of time in which to operate.
I think some votes to close here were due confusion related to an earlier version of the question where the OP experienced technical difficulties. The objection that the OP's SBTMs are finite state machines is incorrect. Moreover, ...

4

[REOPENED]
The question Lexicographic order on increasing $k$-tuples by a first-time poster was closed as "unclear what you're asking". I have rewritten it so that (I think) it is now clear. It is not a hard question, but I think it probably has a nice answer.

4

[REOPENED]
This question was heavily downvoted and closed: When a compact topological manifold with boundary is a ball? Color me ignorant, perhaps, but I wondered if it were as trivial as the downvotes and closure might suggest.
Although it is a question for the topological category, a very similar question but for the smooth category was upvoted and ...

4

The question has now been undeleted (revisions/timeline).

3

[REOPENED]
Question on a concrete example of n points has been improved considerably since it was closed and might be considered for re-opening.

3

[REOPENED]
The question
The probability for a streak when tossing a coin
was closed quickly, but as far as I know, this is not an exercise. There is a complicated approximation in Feller's classic text.
As suggested in this question, I put more discussion in a separate thread.

3

[REOPENED]
Please have a look at the comments at https://mathoverflow.net/questions/135605/how-to-discover-counterexamples-and-required-objects? and consider voting to reopen.

3

[Undeleted; Reopened]
If normal with respect to prime base then normal for all bases was closed as not being research math. I nominated it for reopening, after leaving a comment establishing its research content. There were four votes to reopen; then, OP chose to delete the question.
So now I am asking for the question to be undeleted and, should that ...

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