Figure[Black to move]

We turn from exchanges that upgrade or loosen a target to exchanges that draw a target into position. We saw earlier that a king’s knight in its natural first position—here, on f6—often can give check while unmasking an attack if the enemy king can be drawn forward onto the second rank. Here is another example. Notice the kernel of a discovery: Black’s f6 knight masks his queen. Examine the queen’s possible target and see that the bishop on g5 is loose; it appears to be pinning Black’s knight to his queen, but its unprotected status makes it possible to turn the tables. Black just needs a target for his knight to attack as it moves out of the queen’s way. As yet it has nothing; but Black looks for any check he can give and finds Bxf2. If White responds with Kxf2, now Black plays the discovery Ng4+ and wins back the bishop with QxB on his next move, netting a pawn and damaging White’s defenses with the sequence. (If White replies initially with Kd2 rather than KxB, White has achieved a similar result more simply.)