The diagram position is an elegant miniature composed by Nunn and first published in 1984. It is White to play and mate in three. Nunn the player would probably take the knight with 1. Bxh7 and give his opponent a withering look for not resigning, but Nunn the problemist demands perfection.
The first point is that if White could pass, the problem would be solved. Any move of the black knight allows Qf6 mate, while 1 . . . Kf4 falls to 2. Qe3+ Kg4 3. Qg3 mate and 1 . . . d4 2. Qc5+ leads to mate after 2 . . . Kf4 3. Qf5 or 2 . . . Ke6 3. Bf5.
So all White has to do is keep his queen in touch with f6, d4 and e3. Unfortunately, it can't be done. Also 1. Kxh7 loses the mate after 1 . . . d4 and 1 . . . Bxh7 loses control of h5 in the variation with 1 . . . Kf4. So what White has to do is lose some of his ready- made mates and find a move that substitutes others. The best clue is to ask where you want the queen to go after 1 . . . Kf4.
The solution is 1. Qc6] surprising because it gives the black king more freedom. Knight moves are still met by Qf6 mate, but 1 . . . Kf4 is now answered by the subtle 2. Qc3] with Qg3 mate to follow. Best of all, 1 . . . Kd4 now allows 2. Bxh7 when the king must return to e5 and be mated by Qf6 again.
The final feature of this composition is that if we begin with the position after White's key move, 1. Qc6, it is still a sound three-mover with 1. Qb6] the only solution.Reuse content