Lisp Books

So I aquired the CLOS book and CLtL2 and read a bit in these two and the UCI Lisp manual. Apparently in old Lisps there were functions which were used purely for their sideeffects, such as MAP which always returns nil regardless of it's parameters. When I saw PROG2 for the first time, I thought it was a optimized PROGN for only two forms, little did I know that the 2 means the value of the 2nd form will be returned instead of the last form. in LOOP AS and FOR are interchangeable, though I prefer the latter one.