欧博官网What is perpetual check?
FIDE Laws of Chess do not recognize "perpetual check." They only recognize a case where the same position appears 3 times on the board. If it does, the player about to make the move that will cause it to appear for the 3rd time may claim a draw, but must do so before he makes his move. Once he makes his move, he no longer has any rights to claim a draw, because this can only be done while the player is still "on move". Once he moves, his opponent is "on move".
The term "Threefold Repetition" is widely used, but misleading. Many players take it to mean what it seems to say, that a repetition has occurred 3 times, i.e. the position occurred once (no repetition), then again (1st repetition), then once again (2nd repetition; draw claim already available), and then one more time (3rd repetition, but 4th occurrence of the position; draw claim still available). It's quite possible that 2 repetitions may occur, but the opponent may then vary to avoid a draw claim, in which case the 3rd repetition would not. If this came about, the player who wanted to claim a draw missed his chance, and he won't get another.
It pays to understand the rules, not just know what people call them.