I wonder why we can't declare a question posted on MSE (like this) an exact duplicate of a question posted on MO (like this) and viceversa? (I'd find it useful if we could do this.)


1 Answer 1


My opinion is that questions should only be marked as duplicate only if they are on the same site. For example, if the same question is asked on the site for professional linguists and on the site for English language learners, it requires different answers and different level of detail. Perhaps the difference between MO and MSE is not that big, but there still is a difference. See also this discussion on meta.SO: duplicate questions on other SE sites?

If the two questions, which seem duplicate, are posted at the same time, the best option seems to be migrating one of them and closing as a duplicate. Such opinion was also expressed in a discussion on meta.MO: Close cross posts between here and MSE. If neither of the posts has answers and it cannot be closed as a duplicate, flagging for moderation attention has been suggested as the solution here.

If it is not cross-post, but simply two identical questions, then posting a CW-answer with a link to MathOverflow and some brief explanation seems like a good solution to me. This was suggested here: Closing questions as off topic if they have an answer on mathoverflow? Since this suggestion received 16 upvotes, it seems as a community consensus. (Although this was discussed before MO joined SE network.)

  • $\begingroup$ Regarding your final paragraph, MO migrated on Jun 24, 2013. One day before the question was asked. In fact, the question states that "now that MO is so nearby ..." somewhere inside. $\endgroup$
    – Asaf Karagila Mod
    Sep 21, 2013 at 7:42
  • $\begingroup$ I think cross posting (with a link to the original) to another site when once has not received the answer in one site, gives better exposure to the problem as usually the active user groups in the two sites MO and MSE are different. And I don't see how cross posting in such a situation can damage the social objective of either of the sites of SE in general. Thanks. $\endgroup$
    – triomphe
    Sep 26, 2013 at 18:30
  • $\begingroup$ @MLT Well, several people have said that they do not like posting a question on two sites at the same time. If you have a look at questions tagged (cross-posting), you will certainly find several answers saying this. Personally, I do not have a problem having question on both sites, if the links to the other question are given in both places and if there is a sufficient time gap between them. When they are posted almost simultaneously is the situation, which seems questionable to me. (And, as it seems, to several other users of this site.) $\endgroup$ Sep 27, 2013 at 4:56

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