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It seems that closing as duplicate as the question has an answer on MO is not currently a valid close reason. Coming across this question which has several fine answers on MO (linked to in the comments), I wonder why.

  • $\begingroup$ Legalisms aside...I realize that MO isn't fully part of the network anymore in legal ways I'm not familiar with. $\endgroup$ Commented Jul 11, 2014 at 13:24

1 Answer 1


isn't fully part of the network anymore

Not "anymore"; it never was. MO 1.0 (based on SE 1.0 platform) was separately administered. The current version is operated by SE, and takes advantage of network-wide support functions like DMCA compliance, but is owned by MathOverflow, Inc. See Who owns MathOverflow?

I wonder why

The SE platform has no built-in support for cross-site duplicate closure. It just wasn't designed with the MO/MathSE situation in mind. So, when circumstances warrant, I use custom closing reason: "this question has been asked and answered on MathOverflow". Yes, custom reasons are awkwardly nested under off-topic, but that's just another small limitation of the software.

And when do circumstances warrant this? In my opinion: when both of the following hold.

  1. The question has been resolved to the MathSE author's satisfaction on MathOverflow. (That is, either the author of both posts is the same, or MathSE author acknowledges that MO answers is sufficient.)
  2. The question is not of any wide appeal at all.

Otherwise, I will consider posting another answer on Math.SE: something with a more concrete example, a more detailed explanation, etc. And with a link to MO answer, of course.

(I offer no opinion on the particular question mentioned.)

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    $\begingroup$ Do you really mean "and?" If a question has been satisfyingly answered on MO, and the new question on MSE doesn't explicitly refer to the old question on MO and, say, a particular angle it would like to have opinions on, adding "and is not of wide appeal" sounds like this would rarely apply. In the case at hand, among others everyone's favorite mathematician Terry Tao has chipped in on MO; but I couldn't whole-heartedly say it's of no appeal if Knuth was the first to muse about it. $\endgroup$ Commented Jul 11, 2014 at 14:10
  • $\begingroup$ @gnometorule I did mean and (but this is just my opinion, which is well-known to not always be in line with majority opinion). Seeing 10 positively scored answers on MO, I'd say that a brief synopsis of what's been said by different people over there could make a really good Math.SE answer. Sort of an introduction to a book with 10 chapters. $\endgroup$
    – user147263
    Commented Jul 11, 2014 at 14:25
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    $\begingroup$ Point taken for this question, and this might apply generally: given the research level of MO, maybe a summary in easier terms is usually a valid answer. $\endgroup$ Commented Jul 11, 2014 at 14:30
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    $\begingroup$ But wait - when have you ever disagreed from other opinions here on meta? $\endgroup$ Commented Jul 11, 2014 at 14:31
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    $\begingroup$ Wait, I really disagree with (1) which you edited in, so - for what it's worth - I unaccepted the answer (keeping the +1). $\endgroup$ Commented Jul 11, 2014 at 14:40
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    $\begingroup$ @gnometorule Curses, my bait-and-switch did not work. Edited again. $\endgroup$
    – user147263
    Commented Jul 11, 2014 at 15:44

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