Meindert Niemeijer and László Schór
1.Kc1 eliminates a potential check from b7 and by guarding the rook frees the b1 knight. The threat
2.Se5 threatens three mates 3.Sc4, 3.Sg4 and 3.Re1. The four black defences comprise two pairs
of mutual obstructions: 1...Bxf7 2.Bg5 and 3.Bxf4; 1...Rxf7 2.Sa3 and 3.Sc4; 1...Bxh5 2.Bb6 and 3.Bxc5;
1...Rxh5 2.Sc3 and 3.Sd1. The d6 pawn prevents a second threat 2.Sd6 and a dual 1...Bxh5 2.Be7.
Rodney Topor, Robin Hill and Roddy McKay note that the problem is a sound block with the same key if the S on f7
is replaced by a P or B. Essentially the only function of the threat 2.Se5 is to highlight the intended
obstruction defences by concealing the fact that all of the other R and B moves lead to one or more of the
thematic continuations.
Roddy McKay: A very clever three-mover where the four thematic defences move a black piece to a square
which the other black piece needs at move 2.