In the previous diagram you can replace the bishop with a pawn on g6 and the principle still holds. But the bishop’s ability to rush to g6 from some distance away creates a neat pattern you need to know. Here White’s queen and bishop both are trained on h7; how does he turn this into a win? It would be easy if f8 were blocked, for then Qh7 would mate. But where f8 is open like this, the king often can squirm away: 1. Qh7+, Kf8; 2. Qh8+, Ke7. What White instead plays is 1. Bh7+. The king’s only legal move is back to h8, and now White plays 2. Bg6+, Kg8. At first this looks like an odd use of time; White has advanced his bishop and then retreated it, and Black also has moved his king back and forth. But there was an important gain from the exercise: moving White’s bishop from d3 onto g6, because from there it attacks f7 as well as h7—providing two squares where it can support an attack by its queen. Now White plays Qh7+ and has created the same position seen in the previous diagram and mating with Qxf7 a move later. The key position had to be reached in steps (starting with Bh7+ rather than Bg6) so that Black’s king remained in check throughout the sequence, leaving no time for it to flee or for Black to play f7xB.