The game of Tic-tac-toe is played on a large square divided into nine small squares.
+----+----+----+
| X | O | |
+----+----+----+
| X | | |
+----+----+----+
| O | O | X |
+----+----+----+
- Each of two players in turn places his or her mark-usually X or O - in a small square.
- The player who first gets three marks in a horizontal, vertical, or diagonal line wins.
- A player will always place his or her mark in a line that already contains:
(a) two of his or her own marks or:
(b) two of his or her opponent's marks
thereby giving (a) priority over (b)
- Only the last mark to be placed in the game shown above is not given.
Which mark - X or O - wins the game?
