If there is an answer to a question that I have asked on MathOverflow or MathStackExchange which helps me to prove a result appropriate for a published paper, what should I do:
(1) Cite the MO or MSE question as a bibliography item.
(2) Mention the username of the one who answered my question in the acknowledgements or where my question is cited.
(3) Email the one who answered my question, and ask him/her what he/she prefers, including adding him/her as a second author of the paper; the problem is that it is not always possible to find his/her email address, especially when the username is not the exact name of the user (as in my case..).
I guess that an answer to my current question depends on how significant the answer on MO or MSE is for the proof of the result in my paper; well, the answer in itself is quite 'trivial' either because a graduate student can understand it or because it relies on a known result in another field of mathematics (after being familiar with the known result, my question becomes easy).
Thank you very much.