It would be very helpful if we could vote to close questions as exact duplicates of questions on MO.

edit to consolidate some ideas fleshed out in the comments on Thomas Owens's answer:

  • Having the possibility to close a question as a duplicate of an MO question does not mean that all questions that are (partial or exact) duplicates have to or will be closed as such. In particular, I think that if the question is likely to generate new/different answers here than it did on MO, it's worth having here separately.
  • Closing a question as an exact duplicate of an MO question would create a prominent link to the MO question so that anyone coming across the question here should readily be able to get to the MO question with the answers.
  • It's only worth closing as an exact duplicate if the MO question provides a complete answer (or set of answers), so that any answers here would be duplicating those on MO (people spending time unnecessarily redoing the work of answering, people copy/pasting answers from MO, or people answering with links to MO).
  • I'm not saying that a question posted on MO is off-topic here. In fact, I believe that any question (properly) posted on MO is inherently on-topic here.
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    $\begingroup$ As long as we keep in mind that being an exact duplicate does not always warrant closure. $\endgroup$
    – Larry Wang
    Commented Jul 28, 2010 at 20:27
  • 2
    $\begingroup$ I think the case that was discussed on the other thread (when the question was closed as too elementary but is appropriate here) is still ok. $\endgroup$
    – BBischof
    Commented Jul 28, 2010 at 20:32
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    $\begingroup$ This feature would be useful, but it shouldn't be used too often. MathOverflow answers may often be much harder to understand because they are directed at a different audience. $\endgroup$
    – Casebash
    Commented Aug 14, 2010 at 6:18
  • $\begingroup$ Related: meta.stackexchange.com/questions/16703/… meta.stackexchange.com/questions/151729/… $\endgroup$ Commented Nov 26, 2012 at 2:29

2 Answers 2


I don't see why - could you explain your thought process? From my perspective, the existence of MathOverflow has nothing to do with anything here. In fact, life should go on as if it doesn't exist because this is a totally separate site.

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    $\begingroup$ In my head, the target question is one for which there is an identical question on MO with suitable answers there such that the best answer here would most likely be either pointing to MO or copying an answer already on MO. $\endgroup$
    – Isaac
    Commented Jul 28, 2010 at 20:48
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    $\begingroup$ In particular, if the answers here would be a subset of the mathoverflow answers (due to fewer research mathematicians), it is worth closing as a duplicate. If the broader audience here would contribute more/better answers (easy to imagine for some applications/examples questions), it should not be closed. $\endgroup$
    – Larry Wang
    Commented Jul 28, 2010 at 22:58
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    $\begingroup$ Perhaps topicality should be clarified to make research mathematics off-topic here and then direct users to MathOverflow? If the question is a good question, I don't see why they should be discouraged. Some people might not feel comfortable on MO, but can still provide a new insight here. $\endgroup$ Commented Jul 28, 2010 at 23:25
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    $\begingroup$ For me, it's not at all an issue of on-/off-topic. I'd guess nearly every question asked on MO should be considered on-topic here. I do, however, think that if a question is already well-answered there and asking it here is only going to repeat those answers, it would be more useful to point the asker (and anyone else who comes across that question here) to the existing question on MO. $\endgroup$
    – Isaac
    Commented Jul 29, 2010 at 23:08
  • $\begingroup$ You should link to that question as well, perhaps in a comment. But having more answers just means more words for Google to index and allows random people searching for an answer to find a question on some site (hopefully a StackExchange, either Math or MathOverflow) that gets them the info they need. That's the biggest thing. $\endgroup$ Commented Jul 30, 2010 at 20:11
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    $\begingroup$ I believe that Close as Exact Duplicate causes a prominent link to the question being duplicated to appear on the question being closed, so my suggestion was in part to create the link as you've suggested, but more prominently than just a comment. As to "more answers," I think if the question were likely to generate more different answers here, then it should be left open, but if it's only going to generate duplicate answers, closing it saves people from spending time duplicating work already done and prevents people getting rep from copy/pasting from MO. $\endgroup$
    – Isaac
    Commented Jul 30, 2010 at 20:29

I agree that this feature would be very useful. My main concern is that there is a huge chunk of questions on the unanswered queue that have been crossposted to MO, to a point that browsing the queue sorted by votes or reverse chronological order is pretty much useless. I only see two valid objections to OP's solution.

The first one is that MO is a separate site and might stop existsing (unlikely, but sure, possible). If that's a concern, a better solution would be to have a community bot quote and link accepted answers from MO in the MSE post. But this would be probably too complicated to implement. Manually copying answers as community wiki could also be an option, but it is also prone to synchronization issues (answer being updated on MO but not on MSE), and also would take much more effort since you would have to regularly check whether there are any definitive or accepted answers before copying them to MSE. Instead, marking as (cross-)duplicate can be done from the get-go, e.g. by the poster themselves when they crosspost to MO.

The second one is that the audiences in both sites are different, so it might still be valuable to leave a question open in both places. (I have yet to see a single example where an original answer, essentially different from all the MO answers, was posted on MSE but not on the MO duplicate. But sure, it is a theoretical possibility.)

A solution that addresses both concerns would be to introduce a feature that allows marking a question as a cross-duplicate without necessarily closing the question here, and that removes the question from the unanswered queue. Essentially, a button to add a big banner at the top of the question with a link to the MO question. Even better if this feature mirrors the state of the MO question, especially the answered/unanswered status. Even better if this is a symmetric feature that is added to MO too (but this is outside this community's control.)

The objection to this solution that I predict is that it is too complex to implement. If so, I still believe that OP's solution is best overall for the reasons explained above.


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