How it works
A maze is built fresh every time — six sizes, from four by three up to six by six —
so the game cannot become a memory test. The screen says how few steps the maze can be
done in, and that number is worked out rather than guessed.
When the robot hits a wall it stops, and the arrow that caused it keeps a red cross
after the robot returns to the start. The cells it walked through stay lit. Both are
there to answer "what went wrong?" rather than to say "wrong".