In this thread I suggest the use of the Dot Conjecture, without detailing it, because that would be doing his homework. However, I’m not sure what the copyright situation would be if I had cause to detail it. Reproducing a proof with an author’s commentary would clearly raise copyright issues, but what about the proof itself? What if I commented on it myself?
I believe that facts are not copyrightable, but the presentation of them is. So if you copied an English-language proof directly out of a book, that’d be a violation. If you restated the proof in your own words, that would be OK. I’m not sure, though, if it would be a violation if you exactly copied a formal symbolic representation of a proof.
Thanks, interesting point there; by the nature of the beast, it’s different than our usual Fair Use guidelines, but of course it would be. The ruling even makes sense.