If the bishop moves to e1 then the white king is freed and if the bishop moves elsewhere on the g1-b6 diagonal then the g3 pawn stays unprotected. With these in mind the story is for white to bring the same diagram position but with black to have the move! What would black play then? Black will have to play …f4.
1.Rg5! Kf6
[1…f4 2.h6 Bd4 3.h7 Bg7 what else? 4.Rg4 and the f4-pawn falls +-]
2.Rg8! Kf7 3.Rg6! (here we are!) 3…f4
[3…Kf8? 4.h6 Kf7 5.h7 Bd4 6.Rg8+-]
4.Rg4 Be3 5.h6 f3 6.gxf3 Bxh6 7.Rxg3 and white wins.
If the bishop moves to e1 then the white king is freed and if the bishop moves elsewhere on the g1-b6 diagonal then the g3 pawn stays unprotected.
With these in mind the story is for white to bring the same diagram position but with black to have the move!
What would black play then?
Black will have to play …f4.
1.Rg5! Kf6
[1…f4 2.h6 Bd4 3.h7 Bg7 what else? 4.Rg4 and the f4-pawn falls +-]
2.Rg8! Kf7
3.Rg6! (here we are!)
3…f4
[3…Kf8? 4.h6 Kf7 5.h7 Bd4 6.Rg8+-]
4.Rg4 Be3
5.h6 f3
6.gxf3 Bxh6
7.Rxg3 and white wins.
Pharaoh