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Ultimate Tic-Tac-Toe is an extended version of the traditional game of Tic-Tac-Toe; it involves two players and a large board split into nine small games. The object is to win three small games of Tic-Tac-Toe in a row, column, or diagonal to win the large game. A small game that results in a tie does not count as a win for either opponent in the large game. Each player's move is based on the opponent's previous move. If your opponent played in the upper-right in a small game, you must play in the upper-right game, and so on, even if that game has already been won. If you are sent to play in a small game that is full, you can play anywhere.
Special thanks to the University of Illinois NetMath Program and the mathematics department at William Fremd High School. (June 2016)
Contributed by: Amy Chen and Elisa Kim
Based on a program by: Michael Schreiber
Open content licensed under CC BY-NC-SA
Snapshot 1: even though X won the upper-middle box, players are still forced to move in it if sent there
Snapshot 2: X wins the game
Snapshot 3: X and O tie
 B. Orlin. "Ultimate Tic-Tac-Toe," Math with Bad Drawings (blog). (Jun 8, 2016) mathwithbaddrawings.com/2013/06/16/ultimate-tic-tac-toe.
 Vikesh. "Ultimate Tic-Tac-Toe." (Jun 8, 2016) vikeshkhanna.webfactional.com/ultimate.