Tic Tac Toe

A player can play a perfect game of tic-tac-toe (to win or, at least, draw) if they choose the first available move from the following list, each turn, as used in Newell and Simon's 1972 tic-tac-toe program.[14] Win: If the player has two in a row, they can place a third to get three in a row. Block: If the opponent has two in a row, the player must play the third themselves to block the opponent. Fork: Create an opportunity where the player has two threats to win (two non-blocked lines of 2). Blocking an opponent's fork: Option 1: The player should create two in a row to force the opponent into defending, as long as it doesn't result in them creating a fork. For example, if "X" has two opposite corners and "O" has the center, "O" must not play a corner in order to win. (Playing a corner in this scenario creates a fork for "X" to win.) Option 2: If there is a configuration where the opponent can fork, the player should block that fork. Center: A player marks the center. (If it is the first move of the game, playing on a corner gives the second player more opportunities to make a mistake and may therefore be the better choice; however, it makes no difference between perfect players.) Opposite corner: If the opponent is in the corner, the player plays the opposite corner. Empty corner: The player plays in a corner square. Empty side: The player plays in a middle square on any of the 4 sides.