Weekly Problems 2025-B

Both white knights will need to move in each twin – to guard flights and to give mate respectively – but one gets pinned if Black shifts the f7-rook or the e7-bishop to self-block on f6. In part (a), the thematic try 1.Rf6? Sf7 (unpinning the other knight) followed by 2…Sh4 fails only because Black lacks a waiting move (e.g. 2.Be~? checks). The solution switches the two knights’ roles and moves the black king to the square where it will begin in (b): 1.Bf6 Se7+ (unpinning the other knight) 2.Kg5 Sf3. In part (b), the solution of (a) becomes the thematic try, with 1.Bf6? Se7 and 2…Sf3 failing as there is no waiting move for Black (e.g. 2.Rf~? checks). The try from (a) now works as the solution, because the king starting on the “wrong” square allows a tempo to be spent on returning it to the “right” one: 1.Rf6 Sf7+ 2.Kf5 Sh4. Black’s tempo play is enhanced by the paradoxical twinning of the king. The self-blocking moves to f6 are also Grimshaw interferences that enable mates on f3 and h4, anticipating that the king’s move will unmask a line of defence.

Andy Sag: Looks easy at first glance but great care is necessary to avoid checks on the white king.
Satanick Mukhuty: A lovely juxtaposition of Grimshaw and Umnov! Funny how, when you place the black king on f5, it’s mated on g5 – and conversely, when you put it on g5, it’s mated on f5.

The out-of-play c8-knight has two natural tries that threaten 2.Rxd5. 1.Se7? handles 1…Bg2 with 2.Sxf5, but 1…Ra5! refutes, while 1.Sb6? meets 1…Ra5 with 2.Qc4, but 1…Bg2! refutes. The key 1.Rd7! threatens 2.Qe5+ Kc4/Kc5 3.Qxd5, against which the main defences seen in the try phases are playable. 1…Bg2 enables 2.Se7 with the threat of 3.Sxf5, which leads to either the self-block 2…Be4 3.Se6 or the switchback 2…Bh3 3.Rxd5. 1…Ra5 similarly allows 2.Sb6, threatening 3.Qc4, and this branches into the self-block 2…Rc5 3.Qe5 or the switchback 2…Ra4 3.Rxd5 (2…Rxb6/Rb4/Rc3 3.Qc3). Two elegantly matching variations illustrate the Swiss theme, a logical style idea that involves changing White’s threat. Initially, the thematic tries 1.Se7? and 1.Sb6? carry the threat of 2.Rxd5. But after the preparatory key 1.Rd7! enticing 1…Bg2 or 1…Ra5, the respective knight moves 2.Se7 and 2.Sb6 entail new threats – 3.Sxf5 and 3.Qc4 – that Black cannot parry without creating more weaknesses.

Andy Sag: Giving the queen access to e5 looks attractive but precise placement of the rook is required (1.Rd8? Rb7!). The need to delay correct use of the c8-knight to the second move (in the two main variations) is not so obvious.
Satanick Mukhuty: Interesting logical problem showing self-block decoys! Note that 1.Rd8? with the same threat fails to 1…Rb7!, pinning the white queen.
George Meldrum: The key rids Black’s annoying pin on the white queen with …Rb7.  The variety of possibilities the setting holds makes it more difficult to solve.