What do you think this will return (i.e., T or NIL): (= (factorial 1999) (/ (factorial 2000) 2000)) where FACTORIAL is the obvious non-tail-recursive implementation of the factorial function? (Remember that (factorial 2000) is a VERY big number.) Well, I tried it. After three garbage collections, it finally returned with --- did you guess it? --- T !!! Hats off to the T implementors! Ashwin. -------