Here is an extension of the principle. Black’s king looks vulnerable since it has no flight squares and the h-file is open. A natural thought might be 1. Rh8+, KxR; 2. Qh5+ (or Qh1+), Kg8; 3. Qh7#—mating with cover from the bishop on d3. But after White’s Qh5 Black can interpose his queen on h6 and stop the sequence. So White needs a different idea and turns to the trick described a moment ago: 1. Bh7+, Kh8; 2. Bg6+, Kg8. White simply has moved his bishop to g6, but he has given check with every move and so has kept firm control of the initiative. Why is the bishop stronger here than it was on d3? Because now it blocks the path to h6 of the Black queen, which no longer can be interposed. The rest of the mate is simple: 3. Rh8+, KxR; and White has cleared his own rook from the h-file to make way for his queen while also decoying the king onto h8 where it can be checked. 4. Qh5+, Kg8; 5. Qh7#. Black could have played QxB in the midst of this if his king hadn't constantly been in check.

Now a few afterthoughts:

1. Imagine the same original position but with a Black pawn on h7. Black’s king then looks enormously secure, as his castled position is intact and his queen helps defend it. White nevertheless mates with the same moves described above.

2. It is common for a defender to sit on f6, as Black’s queen does here; often the knight takes that position early in the game and stays there a long time. Eliminating that defender becomes important in building a mating attack. A disadvantage of the queen compared to the knight is shown here: a queen can be eliminated by being blocked.

3. In addition to acquainting you with sequences that can lead to mate, another purpose of these studies is to show useful things your pieces and pawns can do if you can land them on particular squares—especially advanced squares near the enemy king. To recap the most recent examples, we have seen here that a bishop on g6 usefully can seal off f7, h7, and h5 to the enemy king, can provide cover on those squares for its own queen—and, here, can block the path to the h-file of an enemy defender on the sixth rank.