Chess

In the early days of chess problems, positions were made as gamelike as possible, even if that meant the addition of irrelevant pieces, and the solutions were usually a single line of checks and sacrifices.

Modern problems usually have more variety, but here is a recent composition in the old style. It is White to play and mate in six, by Alexander Feoktistov. By convention, Black is assumed to be able to castle unless you can prove that he cannot legally do so. The task, therefore, is to find a sequence of mate theats that allow for Black's castling.

The start is easy enough: 1.Qa1 forces 1...Rxf5 (to stop Qh8 mate) since 1...0-0-0 2.Qxa7 mates quickly. Now comes the clever bit: 2.Qh8+ Rf8 3.Nf6+! exf6 4.Qh1! 0-0-0 5.Qa8+ Bb8 6.Qa6 mate!