This lovely problem by the German composer Fritz Giegold (first published in 1958) had an infuriatingly hidden theme. It is White to play and mate in four.

With the black king just awaiting execution, it is clearly only a question of getting the white queen or rook to join the attack, but that is not such an easy task. After 1.a6 bxa6 2.Nxa6+ Kb7, Black will be able to survive for two more moves.

The next idea must be to get the queen on to the diagonal to a7 to support the bishop's efforts to mate on that square. But when we try 1.Qa3, we see the difficulty: 1...cxd3 2.Qxc5 is stalemate. So what about playing 1.d4 first? That doesn't work either: 1...cxd4 2.Qa3 d3 and Black has concocted another stalemate trap. White can give Black some moves with 1.f4, but after exf4, Black can flick in f3 with check to delay things by another move.

We have found all the components; all we need now is good timing. Here's the answer: 1.Rh1!! cxd3 2.Qg1! c4 3.f4! (perfectly on time) 3...exf4 4.Ba7 mate. Bravo!