I've just been having a discussion in comments here where I referred the poster to the help on cross-posting. I've been told that I'm wrong (which, given how often I am wrong, hardly comes as a shock to me), and the help is misinformed.

I'm happy to be educated, but if the help is wrong, or even incomplete (and consequently, the actions of the moderators and some of us ordinary users here thereby misplaced), something really ought to be done about it. At the least we ought to clarify the situation here in meta. So what is the situation?

The nearest relevant meta post here on CV I can locate is this one, but I expect that Michael will tell us that, that, too, is based on the same misinformation. I think Michael ought to have the chance to put his case that I – and anyone else making the same error – have been doing it wrong, because if we have, we should change that. I have invited him over, so that we don't spam the comments in CV, and here in an answer there's plenty of room to make the point, rather than the tiny space in comments. But anyone's take or some pointers to better information is great.

  • $\begingroup$ Would it perhaps be helpful for future visitors/searches to change the title here into something more informative, e.g. "Is cross-posting allowed on StackExchange?" or some such? $\endgroup$
    – amoeba
    Commented Aug 18, 2017 at 15:14
  • $\begingroup$ @amoeba Ordinarily the help would be pretty much the last word on such a question (if you ask the plain question, whatever the help said would normally be the entire answer). This question is explicitly intended as a question about whether the text of the help is actually wrong --- as had been claimed by Michael Hardy, because if it's wrong it would have to change! I'd say that the conclusion is that it's not so much wrong as it has some potential exceptions. I might consider a modification that didn't lose that central "is the help actually wrong?" aspect $\endgroup$
    – Glen_b
    Commented Aug 18, 2017 at 21:46
  • 1
    $\begingroup$ Maybe something like "Is the help wrong when saying that cross-posting is not allowed?". This would be more explicit about what the issue is actually about. $\endgroup$
    – amoeba
    Commented Aug 18, 2017 at 22:00
  • $\begingroup$ Thanks, that's a clear improvement... edited $\endgroup$
    – Glen_b
    Commented Aug 18, 2017 at 22:03

2 Answers 2


I had debated on posting a similar question awhile ago so I have collected a few links on the subject.

I think it is easier to speak in terms of potentially irksome behavior and try to limit that specifically as opposed to the obverse. For me, things I find irksome are:

  1. Not linking to the other discussions
  2. Cross posting multiple questions immediately

The first should always be done and is not in debate as far as I can tell. The second seems to have less agreement, for both how long is reasonable to wait and whether you need to wait at all. Some of the motivation for cross-posting immediately is stated to ask the question to different audiences. I am not very bemused by this answer, as it is IMO a good indication your question is either subjective or lacks information that would make one receive similar answers on different sites. In combination without linking is taking advantage of the goodwill of the community to help, as one is likely in many circumstances to receive duplicated answers across sites.

I'm not sure what suggestions to give as to how long is reasonable to wait. I would personally say multiple days if not a week or longer - others seem to have different expectations though as to how fast questions are answered (a good question for the data explorer when I get a chance).

Either case I don't think the linked question by Michael Hardy is irksome. He waited a day and cross-posted. Last I knew MathOverflow wasn't a stackexchange site, so migrating isn't even an option.

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    $\begingroup$ (+1) Regarding migration, etc.: MathOverflow 2.0 is a StackExchange maintained site, with some mild caveats that they operate under a different ownership structure and have their own ToS and rules. $\endgroup$
    – cardinal
    Commented Dec 17, 2013 at 19:13

math.stackexchange.com has long been here, and mathoverflow.net, which has functioned for, I suspect, about five years, only recently got absorbed into stackexchange.

The vast majority of questions appropriate for math.stackexchange.com are not appropriate for mathoverflow.net, but perhaps any question appropriate for mathoverflow.net would also be appropriate for math.stackexchange.com. It has long been customary that a question posted math.stackexchange.com that gets no attention there may be cross-posted to mathoverflow.net provided that they're the sort of questions appropriate for the latter forum, and also provided that one states that one is cross-posting, with links in both directions. This became customary long before mathoverflow.net recently became a part of stackexchange.

Thus it is incorrect to say that all stackexchange forums consider it always wrong to cross-post.

  • 3
    $\begingroup$ Thanks for coming in on this. I appreciate it. $\endgroup$
    – Glen_b
    Commented Dec 18, 2013 at 22:57
  • 6
    $\begingroup$ This is an interesting point. It may well be the case that "it is incorrect to say that all stackexchange forums consider it always wrong to cross-post". However, it seems clear to me that there is a general consensus that cross-posting is typically inappropriate. It is better, if you aren't getting any answers on one site & there is another site that might serve, to try to get your question migrated or to delete your Q on the old site & then repost on the new site. $\endgroup$ Commented Dec 19, 2013 at 4:20

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