A miniature which I showed to some of the participants at this year’s
European Solving Championship in Riga. To my surprise it occupied them
for quite some time (perhaps the mental exertions of the serious solving
had taken their toll). Is it really that difficult?
1.Be6 c4 2.Bd6 c3 3.Be7 Ke5 4.Sc5 Kd4 5.Sb7 Ke5 6.Sd8 Kd4 7.Sc6.
The bishops move into position to keep the king confined, then the knight works its way to the mating square, using a manoeuvre first shown by J.G.Campbell in 1855 (see No. 9 in the article on Campbell under British composers). The final position is an example of an ideal mate. All of the squares around the mated king are guarded or blocked only once, and all of the pieces on the board participate in the mate.
It would seem that the problem is difficult to solve, perhaps because it is more natural to try to drive the king to the side of the board than to seek a mid-board mate.