Originally posted by THUDandBLUNDER
1. Bh4 (not the only square possible) Kc5 (or Kb6 doesn't matter). Black needs to be at a6 in time to prevent the bishop going to a7 and b8.
2.Bf2 Ka6 3.Bc5 (again not the only square on that diagonal). Now black is in zugzwang and has to play with the bishop, away from the save rim square: 3. ... Bg3 (or another square on that diagonal)
4.Be7 forces the black king to come back to prevent Bd8 to Bc7. Therefore: 4. ... Kc5 (or Kb6) 5.Bd8 Kc6. Back to the original position with one difference: the bishop is on g3 where it can be attacked:
6.Bh4! forces the bishop to move (instead of the king as before).
6. ... Bh2 (could be anothe square on that diagonal)
7.Bf2! the black king is too late now to prevent Ba7.
7. ... Bh2 (or other move) 8.Ba7 Bg3 (or other) 9.Bb8 Bg1.
It isn't over yet: 10.Bg3 (or another square) forces 10. ... Ba7.
And now 11.Bf2! and the bishop has no other choice than to take 11. ... Bxf2 12.b8Q +/-.
It still takes a while for white to win this, but nothing too difficult.