I personally believe it to be a very instructive question-and-answer combo, even if the proof is easy by any reasonable standards. Does anyone agree with me about undeleting?

http://mathoverflow.net/questions/66275

Question deleted by S. Carnahan♦ Oct 23 at 7:40

Answer deleted by Rob Simmons Oct 23 at 7:40

These times are way too close to be independent. My guess is that, whoever deletes an answer, the software records is as if it was deleted by its author...

So, now that we have good reasons to doubt that the answer was really deleted by the answerer, why is the thread still deleted?

Same for http://mathoverflow.net/questions/69660 .

Different poster, same problem: http://mathoverflow.net/questions/20449

But why does deleting an account imply deleting the questions? We are not DeviantArt, are we?...

Also, I've undeleted 78437 and 81877, but now I realize that I am not enough of an expert to tell if this was the correct move. In any case, user 18092 ("student") displays a troublesome pattern of deleting questions very soon after receiving answers.

The following questions look okay to me, and people over 10k in the relevant subjects are welcome to comment: 78379 - algebraic topology 77850 - commutative algebra

77077 looks like a good question, except for a missing distribution on matrix entries. I think the questioner gave up for some reason.

I am not ready to think hard enough to judge 44499 and 77143. 69168 looks like a decent question, but the answer was deleted by the answerer before the question was deleted by the questioner. 77356 is about totally disconnected groups - perhaps a bit too simple for MO.

I think we can safely let the rest of the questions stay deleted.

Here are the questions with answers that have been deleted by the owner since 2011-08-01. (as of Dec 1)

8172 44499 49084 50134 50180 50481 50600 55083 66275 69168 69660 73090 73744 75366 76486 76492 76526 76860 77077 77143 77356 77512 77689 77850 77908 78096 78110 78379 78384 78437 78662 79689 80517 81284 81877

Update Aug. 4 2011: The OP said it's okay, so I undeleted the question.

I agree with Pete L. CLark that 63559 is a reasonable question and perhaps should be undeleted. My only reservation (and the reason I did not put it in my initial list) is that the OP answered it himself (albeit with the help of Laurent Moret-Bailly), so I felt he should have more control on this matter.

After all this time I'm still not quite sure what our criteria for undeletion are, but if the idea is "the question contributes non-negatively to the site" then I would say undelete this one.

Also 65599 seems like an okay question to me, and it got a serious, not completely trivial answer by two very serious set theorists. (I don't really understand the question either, but since it is cleanly stated and no one asked "What do you mean?" I take that also to be evidence of its nontriviality!)

Things I don't know enough to judge: It hurt my brain to read 65862. 65599 seems to need a set theorist. 63559 seems to need a number theorist or algebraist.

Some of the answers have been upvoted. I always thought questions with upvoted answers can't be deleted, is that right?

Here are the questions with answers that have been deleted by the owner since 2011-05-01.

25247 31991 34050 58134 61699 63334 63559 63893 64200 64516 65066 65488 65599 65862 65912 67412 67927 68396 68614 68909 68988 70480 70585

Based on a quick look, the following should stay deleted: 25247, 34050, 64516

I feel a little weird unilaterally undeleting 37572, since my answer is really a request for clarification (and unsurprisingly didn't get the 2 votes necessary to prevent deletion).

61920 doesn't seem like a bad question, although Harry deleted his answer before Dan deleted the question.

I've undeleted 57647 and 60737. Weird side effect: Will Merry's answer to 60737 has a vote to delete, since he deleted it before the question was deleted. Should I re-delete it?

I don't know enough to judge 60698, 59877 (which showed up twice in your list), or 58662.

Here are the questions with answers that have been deleted by the owner since 2011-03-01.

37572 44059 53922 55402 57264 57647 57810 58662 59324 59436 59877 59877 60698 60737 61279 61351 61710 61920 63314 63610

Here are the questions with answers that have been deleted by the owner since 2011-02-01.

31661 54866 55201 55231 55838 55838 56555 56560

Here are the questions with answers that have been deleted by the owner since 2011-01-01.

49630 50951 51127 51374 52133 52133 52240 53250 53769

49630 was answered by the owner, so can be ignored. 50951 and 51127 are of the form "what's your favorite X?" so should probably stay deleted.

One thing that's weird is that the answers are all undeleted but now have a vote to delete (something only questions should have). The owners of the answers actually deleted them (look at the revision histories). I deleted the answer which just points the OP to math.SE. It now has a bizarre revision history.

48904 had a good answer, so I undeleted it (and voted up the answer).

50573 is a mess, and the "answer" was actually the OP writing an addendum and unable to get back into their account. I would leave it be.

50584 was "replaced" by 50741. The answer (by Dave Roberts) was reasonably good, but its content was incorporated into the new post with acknowledgement. I would be inclined to leave it alone, or discuss with Martin and Dave before undeleting.

The following may be rescued, but I'm not sure: 48134, 48904, 50573, 50584, 50600

24218 was answered by the questioner, and the question did not seem to make sense.

48100 is a rather elementary ultrametric manipulation that perhaps should have been closed. I don't think there is a reason to rescue it.

48944 is a "tell me about X" question, and the answer is a link to question 35882. No need to rescue.

49345 was already closed, but the comments on the question were reasonably interesting.

49530 would have been closed if it weren't deleted, and the answer is rubbish.

50167 is duplicated in 50600, but with a minor revision. I'm not sure what user FS is trying to accomplish by deleting a question and asking it again. Perhaps the two can be merged.

Here are the questions with answers that have been deleted by the owner since 2010-12-01.

24218 31140 48100 48134 48820 48904 48944 49345 49530 50167 50573 50584 50600

• The comment thread and revision history of 46985 suggests that the question was poorly thought out, or that the OP couldn't figure out how to ask about what they wanted. Notice that the answer was deleted by the owner of the answer.
• 47257 is an "embarrassing mistake" that may be worth keeping.

Note, by the way, that once a <10k rep user deletes a question and leaves the page, she can't get to it anymore. So it's not reasonable to assume that a user really wants to keep a question deleted just because they haven't undeleted it.

Here are the questions with answers that have been deleted by the owner since 2010-11-20.

46906 44923 46985 47257

Ideally I guess we would email the deleters and try to persuade them to undelete of their own accord, but I'm not sufficiently motivated to be doing this.

1. I think the question is interesting and is likely to be useful to somebody in the future.
2. I imagine the answerer would like the thread undeleted.

I'll regularly post updates on this meta thread, following David's suggestion of only looking for questions deleted after the last update. It looks like there will be fewer than a dozen every month, so it won't be much work to keep up.

http://mathoverflow.net/questions/33175 is a "big list" question in combinatorics. It's no worse than many others, but no better.

Harry, http://mathoverflow.net/questions/33799 is one of yours. A basic confusion about homotopy theory, but on a very high level.

I have now checked through 34706, so Qiaochu and I together have checked everything.

http://mathoverflow.net/questions/8576 is a question about elliptic curves and I am not sure about it. It looks like Scott Carnahan edited the question to be more reasonable than it initially was, although I am not in a position to judge the level of the current question.

http://mathoverflow.net/questions/6742 looks like a reasonable, if basic, question in commutative algebra. I am not sure about its level.

http://mathoverflow.net/questions/37847 appears to be a fine question in algebraic topology.

http://mathoverflow.net/questions/36883 appears to be a fine question in knot theory, although I'll note that the answer is from the OP, so it's not as if anyone is being disenfranchised by this question remaining deleted. This is perhaps a general case we should ignore.

http://mathoverflow.net/questions/36346 appears to be a fine question in algebraic topology.

Aaand I've now checked through 34905. As for filtering out questions somebody has verified, can we tag deleted questions with a specific tag for this?

It seems to me MO has narrowed its focus since we started. We used to welcome basic questions from someone moving into a new field, as long as that field was something usually learned at the upper graduate level. By that standard, I think this question is fine. But, nowadays, I would expect it to get closed. That's probably a discussion for another day though.

I have now checked through 25416. Besides miwa, and the questions I have linked above, all the others are off topic, offensive, or not research level. I think I am one of the more liberal members of MO, so I doubt anyone will disagree with me on this, but, of course, you are free to look for yourself.

I begin to think that some people are embarrassed when they get a simple answer to their question.

As far as filtering, once you (or someone) goes through that list, then, the next time around, you can delete anything with deletion date before November 2010 from the list.

I searched for questions which had answers and were deleted by the owner. I found 91 such cases, but I don't know what to do with them. I guess I'll post them here so that 10k+ rep users can have a look at them and vote to undelete them if appropriate (in the next comment because of the character limit). Note that 10k+ rep users can also see what questions have the most undelete votes by looking at the delete tab of the tools menu.

I welcome any ideas about how to better deal with this issue. Ultimately, humans have to look at the deleted questions to decide if they're worth undeleting, but perhaps there are better criteria I could use to narrow down the search space. Maybe I should even be widening the search space to include questions that don't have any answers, but do have "substantive-looking" comments. How would I programmatically look for such things?

Also, is there a good way to filter out questions that (somebody has verified) really should stay deleted so they don't add noise to the sample every time I refresh the list?