Unconventional solutions can stump human teachers, also. One day on a chemistry test I was being stupid about how to define "stereoisomer". I knew what it was (two compounds that are mirror images of each other), I was just having trouble expressing it properly. Running out of time I put down "two molecules that are identical if and only if you permit rotation through the fourth dimension." This is extremely unconventional but it is correct--except not only did the teacher not understand it but I couldn't find any help in the mathematics department, either.