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There is no such official rule as 'perpetual check.' The example given falls under rule 10.10, which states that a game is a draw if the same position is reached three times in a game, with the same player to move. This diagram certainly shows that the same position is reached three times in the game. Also, the position doesn't have to be occuring in a row, the same position can be separated by many moves. For example, a position occurs at move 25, then again at move 35 and then again at move 40.