Figure[Black to move]

Now combine the principles we have been studying with one from earlier: the use of a pawn to seal off the king’s flight squares and trap it on the back rank. Here Black’s pawn on g3 attacks f2 and h2, so White’s king is stuck just as it would be if its pawn cover still were in place. Black has a battery of heavy pieces on the e-file, making e1 a potential mating square. White currently defends the square twice, but one of the defenders is his king. We know that when a king defends itself against a back rank mate it sometimes can be pushed away and made defenseless. A queen can do this especially well from up close, because it has the power to first apply bishop-like diagonal pressure and then add a rook-like vertical attack. Black thus begins with Qe2+, forcing White to move his king to g1. Now e1 has just one defender, so Black exhausts it in standard fashion: first comes Qxe1+, to which White replies RxQ; and now Black mates with RxR.