The forty years and the fact the original writer is dead are good arguments. I'm not so sure about: > Simply because the target has money? To be honest I thin

The forty years and the fact the original writer is dead are good arguments. I'm not so sure about: > Simply because the target has money? To be honest I think they probably borrowed the intro from Spirit (they toured together and musical / lyrical borrowing was standard operating practice for Zep), but it was a very minor part of what made the song successful. However the fact the song has apparently made over half a billion dollars in royalties does rather amplify the significance of that minor borrowing.