Today, recently viewed this post on combinatorics asking to prove the famous result "If $p$ is a prime, then $p|{p\choose k}, k\in \{1,2,\dots,p-1\}$". I was fairly sure that, It should have been asked earlier (though I have never seen, as haven't searched this site for this question before, but the level of questions are asked here, I was convinced that this too should have been asked).

So, when I googled "if p is prime then p divides p choose k at math.stackexhange.com", it showed me three questions on this site where this one was asked $10$ months ago, this one was asked $2$ years ago, and this was asked $3$ years ago.

So, my question is,

setting aside the first question which was asked $3$ years ago, why not the other ones were closed?

I am not complaining about any policy of closing, I am just trying to bring this fact to everyone's sight.

I too agree that the newer questions got much attention and marvelous answers than the first question asked $3$ years ago, so if these were closed without answers, we should have been deprived of those various types of concepts of solving this question.

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    $\begingroup$ The more likely reason "why" is that the design of this site makes maintenance of such things very difficult. Unless a question is closed as a duplicate very quickly, it is likely to sit for some time unless or until someone happens to notice it. $\endgroup$ – Carl Mummert Dec 20 '15 at 21:54
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    $\begingroup$ @Carl: the still more likely reason "why" is that the user of the site mainly don't care. Maybe it is not even a bad thing, but to blame the design is quite besides the point and in this unspecific form rather unhelpful in my opinion. $\endgroup$ – quid Dec 21 '15 at 1:05
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    $\begingroup$ @Carl: I'm not the most careful dupe-searcher either, and I stand by the assertion that many users don't care much for finding duplicates. If someone finds a clear duplicate usually the other votes will be found quick enough. Right, it is not instant. But really it has a quiet direct effect. Maintaining this site is difficult because it is large. Things could always be better, but to say it is "very hard" strikes me as an exaggeration. Likely one could try to put more emphasis on it, but this could also have negative side effects. Anyway,the constant nagging about design etc is tiresome. $\endgroup$ – quid Dec 21 '15 at 1:57
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    $\begingroup$ @Carl: "many" can mean all kinds of things. For the majority of users finding duplicates seems certainly not like a particular concern (this includes me, by the way). The point is not whether you ping me or not, indeed I would appreciate you ping when you reply to me. The point is if you badmouth the infrastructure in a non-constructive way. Indeed I would appreciate if you could stop this. Of course one can and should discuss things, but the way you go about it as far as concerns SE is not constructive. I will avoid speculation about the motivation. $\endgroup$ – quid Dec 21 '15 at 2:08
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    $\begingroup$ @quid Pointing out a (well-known) flaw in the design of the platform is hardly " badmouth(ing) the infrastructure in a non-constructive way". I see nothing at all nonconstructive in Carl's remark. $\endgroup$ – Bill Dubuque Dec 21 '15 at 2:11
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    $\begingroup$ @BillDubuque: As you might infer from the time-stamps there are deleted comments. A discussion about comments almost nobody can see anymore seem pointless. Anyway, your stance here is not in the least surprising. But as long as you are here let me do a mini-survey: is finding duplicates a particular concern of yours? $\endgroup$ – quid Dec 21 '15 at 2:37
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    $\begingroup$ Some background explanation for why the system is not designed to make it easy to handle duplicates (to say the least) can be found at blog.stackoverflow.com/2010/11/… and meta.stackexchange.com/questions/90620/… . <shakes head> $\endgroup$ – Carl Mummert Dec 21 '15 at 2:40
  • $\begingroup$ @quid The comments were not deleted when I opened the page, i.e. I saw them all. $\endgroup$ – Bill Dubuque Dec 21 '15 at 2:46
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    $\begingroup$ @BillDubuque Good. Would you answer my question? $\endgroup$ – quid Dec 21 '15 at 2:47
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    $\begingroup$ @Carl: it is very unclear to me what issue you have with the linked material. Unfortunately you do not explain it. Awarding points to dupe-closers may look good in abstract, but being familiar with the debates especially in this community I am virtually certain that in practice this would be a terrible idea. I'm glad it's status-declined. On the blog-post: it seems reasonable to me. Roughly it says: for various abstract and concrete reasons it is neither feasible not desirable to hunt down each and every potential duplicate, but egregious duplication should be avoided. To which I'd say:yes. $\endgroup$ – quid Dec 21 '15 at 18:25

There are many thousands questions on the site, and it's not always easy to find the duplicates. When you do find one, feel free to flag it (or vote to close it) as a duplicate, even if it's old.

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    $\begingroup$ @SubhadeepDey Some misguided users believe no questions should be closed, ever. They believe this website is the same thing as students coming to their office hours and asking questions, where of course telling them "I've answered that question three years ago" is not an option. I for one salute your eagerness to make the site better by cleaning up duplicates :) $\endgroup$ – Najib Idrissi Dec 21 '15 at 8:09
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    $\begingroup$ Let me complement mrf's answer by saying that if answers to two duplicates are sufficiently different and the questions are asked in such a way that the answers to one apply to the other, then moderators have the power to merge threads. In this case you can try flagging one of the questions to expose your case, or go to chat. $\endgroup$ – Najib Idrissi Dec 21 '15 at 8:11
  • $\begingroup$ @NajibIdrissi, in which room I should consult this? Is it Math Mods' Office. I have no experience of chat. $\endgroup$ – user249332 Dec 21 '15 at 8:21
  • $\begingroup$ @SubhadeepDey Yes, for example. There's no real harm in asking, mods are normal people like you and me. You can just go there, say hi, and ask if they think a merge is a good idea. $\endgroup$ – Najib Idrissi Dec 21 '15 at 8:41
  • $\begingroup$ Why not make a "hall of fame" for such questions? :) Or make it wiki, where different answers with different opinions and approaches could be collected. Just deleting questions with answers is not good idea for me... $\endgroup$ – Evgeny Dec 26 '15 at 20:05

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