From page $135$ of Smullyan (right before the Solutions at the end of Chapter 12):
> "Tomorrow," said the Sorcerer, "before we leave this island, I would like us to visit the station of Simon Simpson, who is the youngest and most progressive roboteer on this island. I've heard he is a bit on the vain side, but also that his program system is a very simple and elegant one, and definitely worth learning."
See also the entirety of Chapter 13.