I was re-looking over edition 1 of Simply Scheme and noticed that you did card shuffling correctly! Some people assume that if you simply exchange each card with some other random card, including those that you've already "processed" that that will be a randomly shuffled deck. (I didn't realize that this was an issue until about 2 months ago when I was reading in Chance News that some people were taking advantage of the incorrect way of shuffling on web-based card games and winning big! Pretty funny.)