Chess is a simple game of marvelous depth. Though it uses a small set of deterministic rules and is played out on a board of just 8×8 squares, even the most powerful computers cannot see far into the maze of possibilities that fan out from a complex position. As a result, computers cannot use brute tactical force to defeat a human master’s capacity for long-term strategy and pattern recognition. Instead, heuristics are required, in the form of code used to explore possibilities, recognize powerful piece formations, and so on. Chess programs are exquisitely tuned to discard unlikely lines and to ignore material values in favor of gambits and subtle plans.