Wow.. I saw them do that SO LONG ago at the California Jam.. a huge 2 or 3 day festival in the early 70's. Sabbath, Deep Purple, ELP ...a bunch of others. I was only 13 or 14 years old.
My Dad forbid me to go.. I went anyway and was in the worst trouble of my young life when I got back.
Saw ELP in concert during college...damn, that was an entertaining show!