I'm preparing a talk on American folk songs. I'd be grateful if anyone could offer any information about John Denver's "Leaving on a Jet Plane". I heard a rumour that his copyrighted song is based on one by a folksinger from Nottingham, England. I know for certain that many people have copyrighted "new words and music by...." versions of trad songs, but I doubt that Denver would do that to some other guy's song. Anybody have any details?