White to move! How should white proceed?
I have seen this motif before, but it still took me a couple of minutes to remember it. The key point is that after white takes at d8 with the bishop, the two black rooks communication is cut, so black cannot take immediately at h6- he has to first exchange at e1, but that still leaves the a8 rook vulnerable:
1.Bd8! Re1+ 2.Re1 Nh6 3.Re8+ Kg7 4.Bf6+ wins the exchange.