double check lesson
		Double check is like the most threatening offense move in chess. It works like this. Let's say a knight or bishop is infront of your rook and across there is opponent's king. You move your knight or bishop to a position to give a check. Then you find out that it's double check because the rook behind also gives a check to the king since the obstacle has been removed. In chess, we say this is discovered check. Well, there can be "double-discovered check" That is all the fun part of chess.