It seems to me that my answer at

If $f$ is a smooth real valued function on real line such that $f'(0)=1$ and $|f^{(n)} (x)|$ is uniformly bounded by $1$ , then $f(x)=\sin x$?

deserves to become a little paper; everyone I mention it to is surprised by the result, and I doubt that it's well known. The paper I have in mind would be a considerably cleaned up version of what appears there.

Q: What legalities, protocols, and bits of etiquette are involved in publishing an answer to a MSE question?

In particular, assuming that such a publication is not simply unacceptable: Presumably I'd cite MSE as the source of the conjecture. I imagine there's a standard way to give such a citation, that I can find when I get around to looking for it. In particular squared: Would I cite the author as user228168 or is there a way to find his/her real name for this purpose?

• To see how others dealt with similar situation, you might have a look at the papers mentioned in this post: Papers that originated on math.SE. Maybe some of other posts linked there might be of interest for you, too. – Martin Sleziak Sep 28 '17 at 15:35
• @MartinSleziak Thanks. Just noticed the "cite" link below posts - the existence of that link answers my main question, yes, people do cite MSE in papers. That thread should be very useful regarding various details... – David C. Ullrich Sep 28 '17 at 16:03
• Well, there is a separate tag called (citation) here on meta - currently 29 questions have this tag; as you can see people asked various things about citing posts from this site. – Martin Sleziak Sep 28 '17 at 16:13

Mostly what you say suffices, I think. That is, it seems apt to mention SE as the source of the problem.

There is no mechanism on the site to find out the identity of the user, especially not in the current case where it is a deleted account.

If the account were still active you could mention your intent in a comment and ask for their preferences regarding using their displayname or give their real name.

In the current case, one could say something like: The result of the paper first appeared as a post by the author on the site Mathamatics Stack Exchange, responding to the question of a now anonymous account (user228168) [Reference to the thread.].

Searching one can find the display name used at the time the question was asked. Arguably, you could also use that. But I am not sure it is a good idea.

Regarding legalities, it may be worth recalling that you licensed the content of your answer under a CC license to Stack Exchange. Especially, if you want to reuse the same write-up this could be an issue for some journals but the policy of others is such that it is no problem.

• Thanks. I'm not a lawyer, don't even play one on TV, but I tend to suspect the license should be no problem. The paper I have in mind is substantially different from the writeup in my answer (I fill in various details left fuzzy in the answer, and having done that it turns out that most of what I said in the answer doesn't need to be said...) – David C. Ullrich Sep 28 '17 at 16:57
• You are welcome. I think, but I am not a lawyer, if the write-up is different it should a non-issue; – quid Sep 28 '17 at 17:11
• Incidentally, how does the licence granted on this site compare to the standard arXiv licence? – Tobias Kildetoft Sep 29 '17 at 6:48
• @TobiasKildetoft the license here is BY-SA, that is it requires mention of SE yet allows to redistribute and to modify the content. On the arXiv.org one only gives permission to the arXiv to distribute the content. That mention of SE is required is irrelevant for the present context as OP as author can always relicense to the journal their content in a way that does not require this. An issue a journal might see is that the content is licensed in a way that everybody can distribute it, say, a competing journal could also print the SE content while this is not possible with content on arXiv. – quid Sep 29 '17 at 9:02
• Practically I doubt it is relevant for many journals and not few will even be fine with it. But strictly there could be issues with some author agreements of journals that have some explicit exceptions to allows arXiv and other preprint servers yet those exceptions might not cover SE. I mean things like "This work was not published before except [some list]" @TobiasKildetoft – quid Sep 29 '17 at 9:07