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    Since becoming somewhat more involved with Math.StackExchange, I've started to take more notice of questions that are cross-posted to both MO and MSE, and question that are first posted to MSE and then re-posted to MO. Personally I think the former is just bad form (the same way that cross-posting to USENET groups is often so), but what irks me most is a particular class of the latter.

    Some users seems to think that just because a question is asked on MSE and did not receive the answer that they want, the question should be automatically upgraded to MO. In some cases this is warranted: the user may have hit upon a question that is of reasonable research interest, or one that is sufficiently thought out and clearly written that a real expert can easily spend five seconds of his time giving an answer. In many other cases, this is not: often part of the reaons that the questions did not get an answer on MSE is because that they are not sufficiently well posed mathematically, and in some cases the questions have limited research interest.

    To me, this feels like an abuse of the MO mandate, as stated in the FAQ (which unfortunately nobody reads).

    Now, my questions/comments:

    1. How can we properly discourage direct cross-posting?
    2. How to respond when a user carries a question that doesn't quite fit the MO scope, but that he/she already asked on MSE and received no answer for? (In particular, the old stand-by "please try asking this on MSE" would be rather inappropriate in this case.)
    3. Related to (2) is I think again an old discussion rearing its ugly head: for us mathematicians we know a research-level question when we see one (some people are more generous than others, so there is a fuzzy belt in the middle, but for large parts I think people agree on what research-level roughly means). But those users whose behaviour this post is trying to affect are precisely those for whom the phrase "research level" just means "difficult". So how do we properly convey the notion that a good question for MO should be one that is well-posed mathematically, and ideally also with some motivation?

    (Tangentially related to (3) is a recent question on MSE.)


    I don't mean to hijack the discussion, but I was wondering if you thought cstheory should be included in the crossposting discussion. We've been trying to encourage people not to crosspost simultaneously on MO and cstheory (with some, but not a lot of success), and I haven't seen any other discussions here on what people feel about this. If you'd prefer to do that in a separate thread (or not at all) that's fine as well.

    @WillieWong: Would you prefer that reposting from math.stackexchange is forbidden altogether?

    Personally, I think that if it isn't forbidden clearly and explicitly somewhere in the FAQ (so that it becomes official MO policy)
    then we just cannot escape from dealing individually with each specific case.
    I don't think it should be forbidden to repost. It is reasonable that some questions that would be appropriate here are to be first asked there. Not every user at math.SE knows of MO. For example, why would be inappropriate?

    On the other hand, I think reposting just a few hours after posting at the other site *is* inappropriate.
    • CommentAuthorWillieWong
    • CommentTimeFeb 5th 2011 edited

    @Suresh: I think this discussion can equally apply to CSTheory, so do share any thoughts you have!

    @Andrey: I think that is too extreme. Re-posting is warranted at times (there was a question which was on Math.SE for 2 or 3 days at least before it got re-posted here [which I was about to do myself if the owner didn't] and received a great answer in 2 or 3 hours). But perhaps direct cross-posting (MO, Math.SE, cstheory) should be forbidden?

    @Andres: I agree. What if I add something in the FAQ of Math.SE to the effect of "be patient, just because your question is not yet answered [in 5,6, 10 hours] doesn't mean that it won't be; many users live on a different time zone from you"?

    I am not sure how practical this would be. Could the following be a useful suggested procedure for the math.SE FAQs, supplementing the adivice you (Willie Wong) give:

    "If you do not receive a satisfactory answer within a reasonable time (a couple of days) and think about reasking on MO, we suggest (in particular, in case you are not regularly active on MO) that you first edit your existing question here adding for example 'EDIT: I am thinking about reasking this on MO. What do others think?' and wait for a while (a day) for feedback, especially by users active on both sites."

    @an_mo_user: I worry that your particular suggestion may be too prescriptive and specific, and some people make take it the wrong way.


    I think this discussion is drifting a bit: suggestions for MSE should be discussed on meta.MSE. Let's try to steer the discussion toward MO.

    A. Is cross-posting really a problem on MO?

    This is unclear to me. I spend a lot of time monitoring annoyances on MO, so far the annoyances associated with cross-posting have relatively low frequency.

    B. What, if anything, should be done about cross-posting?

    Even if cross-posting is not an emergency problem, we can still do something about it. A brief addition to the MO FAQ can't hurt, though it should be carefully worded.

    C. What is the appropriate way to handle cross-posts?

    There are several issues here.

    Ideally, the cross-poster would diligently link to the cross-posted question and its answers to avoid redundancy and confusion. Since users aren't that reliable, I would suggest adding missing links when anyone notices a cross-posted question.

    What if a cross-posted question gets an accepted answer on another site... Should the question be closed (no longer relevant)? Should it remain open for new answers? Should the accepted answer be cross-posted as well?


    @Francois: sorry about the digression. Thanks for bringing the thread back on topic.

    Perhaps the suggestions you list above w.r.t. C should also be included in the proposed MO faq change? That is, something along the line that

    1. Rather than the shot-gun approach of shooting questions simultaneously to MO, MSE, and CStheory, we encourage a more surgical approach of asking the question in the most appropriate forum.
    2. If one must cross-post, please have the decency to provide links to the cross-posts
    3. Perhaps a suggestion for the poster to exercise the power to "close as no-longer relevant" if an answer was received on other sites? That one cannot easily coordinate answer given on different fora is one of the reasons I find cross-posting undesirable.

    Also, back to my questions 2 and 3 (top of the page):

    D. Is there anything we can do to dispel the perception that MO is a "last-resorts" "ask-an-expert" place? I rather selfishly would like MO to stay a forum for research mathematics, and not a forum where "professional mathematicians hang-out and answer questions for which answers were not found elsewhere" becomes the norm.


    This is the policy that we have on cstheory, and it sounds very similar to what is in effect here:

    Crossposting from MathOverflow is perfectly fine, as long as they aren't done in parallel. That is, if you post a question on one site, you should only post to the other site after you have not received a satisfactory answer for some time, and you should provide a link in each post (or in the comments on it) to the other one. As a courtesy, if you post your question here after trying MathOverflow, please try to integrate in your question the answers you received on MathOverflow (even if they did not answer everything).

    At some point I was proposing that we remove the 'in parallel' restriction, but consensus was that we should keep it in place, but enforce gently.

    Suresh's policy summary sounds exactly right to me.
    • CommentAuthorMariano
    • CommentTimeFeb 5th 2011

    (No one reads the FAQ... )