Tic-tac-toe, also called noughts and crosses (in the British Commonwealth countries), X's and O's (in Ireland) and X and 0 (in India) is a pencil-and-paper game for two players, X and O, who take turns marking the spaces in a 3x3 grid. The player who succeeds in placing three respective marks in a horizontal, vertical, or diagonal row wins the game. The following example game is won by the first player, X: Players soon discover that best play from both parties leads to a draw (often referred to as cat or cat's game). Hence, tic-tac-toe is most often played by young children. The friendliness of tic-tac-toe games makes them ideal as a pedagogical tool for teaching the concepts of good sportsmanship and the branch of artificial intelligence that deals with the searching of game trees. It...'
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