I dunno. When I first read Norvig's beautiful solution, I immediately thought, "Only someone coming from a Lisp and (old school) AI background (or maybe a super

I dunno. When I first read Norvig's beautiful solution, I immediately thought, "Only someone coming from a Lisp and (old school) AI background (or maybe a super-Mathy background where everything is a Set) would have picked that representation, but oh man does it work so, so well."