ty is built around it. The neural network has two functions: firstly, to evaluate a position, estimating the probably that the side to play is winning (called <em>value</em>), and secondly, to estimate the probability that each legal move in a position is the best (called <em>policy</em>). In a game like tic-tac-toe, looking at an unfinished game and making an evaluation is not necessary because the engine can see to the end of all lines of play. In chess or Go, even after 7 or 8 back-and-forth piece moves 