Dwight Slade talks about Bills Book on Comedy.

In the dvd extras on the first disc. Dwight Slade talks about a book that Bill carried around that talks about Robert Kline, George Carlin and Richard Pryor. It was a critical book about standup. It must of came out in the late 70's early 80's. You can fast forward to about 18:00 into the extended interviews and it will say "Dwight Slade. Bills book on Comedy." Does anyone have any idea what that book could possibly be?