Mate in 3

There are two thematic tries, 1.Qa2? refuted by 1...Ra4! and 1.Qg2? refuted by 1...Rg4! The key is 1.Qf2, threatening 2.Qg1 and 3.Qg8 and preparing to meet 2...Rg4 with a capture on a7. Black can defend by 1...b4, preparing 2...Rb5, but White can now continue 2.Qa2 threat 3.Rxa7, since the new defence 2...Ra5 allows 3.Qg8. Similarly after 1...f4 2.Qg2 threat 3.Qg8 the new defence 2...Rg5 allows 3.Qxc6. There are two non-thematic defences, 1...Rc5 2.Qa2 Ra4 3.Qg8 and 1...c5, after which both 2.Qa2 and 2.Qg2 will work. The basic structure is similar to last week’s example of the Hamburg theme. Black has a successful defence to a threat, which is eliminated by a decoy, and replaced with an unsuccessful defence. When three black pieces are involved, as here, the theme illustrated is a Wechselform (or Changed-form) Dresden.

Dafydd Johnston: The link between this and last week’s problem lies in the role of the auxiliary piece which causes a good defence to be replaced by a bad one – here doubled with two black pawns closing the line of one rook and opening that of the other. This surely deserved better than 5th prize, but Zepler did also win 1st prize with another excellent problem.