Im 1600 rated player and this took me 20 seconds to solve, is this really considered a very hard puzzle?
The obvious moves dont work, you can see whites pawn moving forward is mate, and you can see black is essentially trapped and has very limited moves, so immediately I thought first move is a waiting move and theres only two options there. Block the black pawn moving and if bishop moves, rook takes is mate. So rook has to block, and you can see bishop either moves or captures and pawn moving forward is mate
The obvious moves dont work, you can see whites pawn moving forward is mate, and you can see black is essentially trapped and has very limited moves, so immediately I thought first move is a waiting move and theres only two options there. Block the black pawn moving and if bishop moves, rook takes is mate. So rook has to block, and you can see bishop either moves or captures and pawn moving forward is mate