I've already got the Abelson & Sussman code. (And now I know it's part of the MIT Scheme distribution.) I'm still looking for more R3RS programs to test my system. thanks, Paul Paul R. Wilson Human-Computer Interaction Laboratory lab ph.: (312) 413-0042 U. of Ill. at Chi. EECS Dept. (M/C 154) Box 4348 Chicago,IL 60680 wilson@carcoar.stanford.edu