Figure[White to move]

Some of the familiar elements from this chapter are in place this time—and some aren’t. The queens aren't aimed at each other, nor does Black’s king protect his queen. On the other hand, White has a rook aimed at d8 and a battery of bishop and queen trained on f7. Those latter elements do not necessarily suggest the precise idea we have been considering, but they do suggest the importance of looking at checks—and especially the Bxf7+ sacrifice. Once White plays that move, notice how few choices Black has in reply. He can't move the king because all of its flight squares are attacked. He's required to play QxB. Examine the aftermath of this simple exchange and see how it has changed matters: now the two queens attack each other, and Black’s queen is protected by his king—so naturally we resort next to a check to prise the king away from the queen. This time White returns to his rook for the purpose, playing the flush check Rd8+ and requiring Black’s king to take his rook: a decoy. Now the queen is loose, and White plays QxQ.

Again we see how any sequence that brings the enemy king and queen into a dependent relationship—by forcing the enemy queen to interpose, by forcing either piece to make a capture and move next to the other, etc.—creates a potential vulnerability.