How should questions that are posted (by the same asker) on Math.SE and another Stack Exchange site be handled?

The general Stack Exchange policy is that multi-posting is strongly discouraged. On other sites where I participate, when a question is found to have been multi-posted, we close it on all but one site. The site is chosen by two criteria:

  • try to pick the site where the question is most on-topic;
  • avoid losing or migrating worthwhile answers.

This is not a written policy (for all I know, I'm the first to write it down explicitly), but it's generally followed on the computer-related sites with overlapping scopes (Stack Overflow, Super User, Server Fault, Unix & Linux, Ask Ubuntu, etc.). What this means in practice:

  • If the question is unanswered everywhere, we close it as too localized on all but one site. (Too localized because having this extra copy of the question doesn't make the Internet a better place.)
  • If the question is answered on only one site, we close it on all but this site.
  • If the question has answers worth keeping on more than one site, we migrate to a chosen destination and merge there.
  • If there are several candidate sites, we try to pick the one where the question is most on-topic, the one where it is most likely to get the best answers.

Example: This question was also posted on Computer Science. Following general Stack Exchange habits, if I'd seen it before it had been answered, I'd have flagged it for closure on Math, because it's a CS question, more on-topic on CS than on Math. If I'd seen it when it had an answer on Math but none on CS, I'd have closed it on CS. Now that it has answers on both, I'd have flagged it for migration from Math to CS. But I don't know if Math.SE adheres to the general Stack Exchange policy in this respect.

Another example: this question was also posted on Computer Science. As I write it is unanswered on both sides. This is math applied to computer science, so I think it could go either way.

Does Mathematics adhere to the general policy? If not, how should we deal with questions that are posted on Mathematics and another Stack Exchange site?

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    $\begingroup$ We also have the issue of questions cross-posted here and on MathOverflow, which is hosted by SE but not on the "network". $\endgroup$ May 8, 2012 at 22:42
  • 6
    $\begingroup$ @Dylan: the main difference is that question migration and merger is done more fluidly between SE2 sites. For example, for the sake of consolidating all the answers in one place, one can argue that the Math version (in Gilles' post) be migrated to CS so that it could be merged with its exact duplicate making it easier to find the various answers to the question at once. For MO and SE sites there isn't a simple migration mechanism that would copy over the comments and answers automatically. $\endgroup$ May 9, 2012 at 7:10

1 Answer 1


There are two kinds of cases I have encountered so far.

  1. If I post a question on one site, and then find out the question might be better suitable for another, I will usually post an identical question on the second site, and delete my original one.

  2. If a moderator finds out my question on his site is better suitable for another one, he or she will migrate my question there, leaving the title of my question and a link to the new one still on the main page of the original site.

Some questions are interdisciplinary, suitable to more than one sites, and having opinions from different perspectives is always exciting. So I wonder if it is a good idea for a user to post a question on one site, and then to post links to this question on other relevant sites? Just my 2 cents.

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    $\begingroup$ That's not what I'm asking about. I'm asking what to do if a question is already posted on two or more sites including Mathematics. $\endgroup$ May 13, 2012 at 18:03
  • $\begingroup$ Perhaps as what moderators do in the second case I encountered? I know my last paragraph is more of a feature request. $\endgroup$
    – Tim
    May 13, 2012 at 18:04

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