Sudoku follows in a long tradition of artificial intelligence research on games, most notably chess. But some of AI's most important advances stem from more modest games. The route-finding algorithm that powers car navigation systems, for instance, was first demonstrated on the Sliding Tile puzzle, a child's toy in which a player tries to move 15 tiles around a grid so that their surfaces form a picture. The same algorithm helps video game characters steer through virtual worlds. "This is an algorithm developed back in 1968 in abstract kinds of things," says UCLA's Korf, who himself has explored algorithms for the Rubik's Cube. "It's used all the time.