Figure[White to move]

Now what? Notice that White still has the kernel of a discovery on the g-file; he can take advantage of it with the double check Nxe6. The king can move to h6, h7, or f7. Consider each possibility.

(a) If the king goes to h6, White mates immediately with Qh8: his queen attacks the king on the h-file and his rook seals off the g-file.

(b) If the king goes to h7 White can bring in still another piece with check: BxN+. Since the pawn on e6 is off the board the bishop can’t be captured; and Black has nothing to interpose. So Black has to move his king again—this time to h6. Now Qh8 again mates.

(c) If Black’s reply to Nxe6+ is Kf7, White then plays Qd7+. Black is forced to interpose his knight on e7; his king has no flight squares (each square the king can reach on the back rank is attacked by a different White piece!). Now White mates with Rg7, as shown in the next diagram—the last of this sequence.