Weekly Problems 2026-B

The white king has four diagonal flights, and the two eventual mating moves by Black’s queen and e8-bishop will cover different pairs of these squares. In both cases, White needs to self-block the two remaining flights, so the rooks are unpinned for this purpose. The white queen and h7-bishop take turns to unpin one of them, which then frees the other. Once both rooks have carried out their self-blocks, the self-pinned queen or bishop moves along the pin-line to give a deflecting check, which forces a diagonal pin-mate. 1.Qh1 2.Qc6 3.Rd4 4.Rc4 5.Ra2 6.Ra6 7.Qd7+ Bxd7 and 1.Bg8 2.Bc4 3.Re6 4.Rc6 5.Ra7 6.Ra4 7.Bd3+ Qxd3. Two attractive sequences with perfectly matching effects, including how the rooks switch the lines on which they are pinned.

George Meldrum: Nice pair of complementary solutions. Had initially thought that a king march may have done the trick: Kc6-d6-e7-f8-g7-h6-h5, Qh3+ Qxh3, but alas that was eight moves.
Andrew Buchanan: Very satisfying. The unguarding and re-guarding of the white squares adjacent to the black king is particularly cute.
Satanick Mukhuty: Beautiful harmony of unpin and self-pin in the two phases!

In this complete block position, white mates are prepared against all possible black moves. Thus, 1…Q~ unpins the white queen and allows 2.Qd3, while 1…S~ is an unguard that enables 2.Rxb4. White has no way of preserving this zugzwang, however, and any king move (which creates threats) is foiled by a queen check, e.g. 1.Ka1? (2.Qd3/Bb1) Qd4+!, 1.Kc1? (2.Qd3/Bb1) Qc4+! The key 1.Sg2! (waiting) puts the knight in control of e3 instead of d3. This leads to changed mates for all three black queen moves, 1…Qd4 2.Qc2, 1…Qc4 2.Qxc4, and 1…Qxa4 2.Qd5, where the white queen must choose each mating square with care. 1…S~ 2.Rxb4 is unchanged. An unusual mutate in which one unpin variation in the set play is expanded to three after the key.

Bob Meadley: 1.Sc2? a good try but 1…Qd4! Very tough for me and a nice simple looking position.
George Meldrum: A masterclass of changed play from set play.
Satanick Mukhuty: A great mutate with three mate changes achieved with just eleven units. The try 1.Sc2? also contributes to the content.

Three white pieces are controlling three different flight-squares on their own: the rook guards e5, the d3-bishop guards e4, and the knight guards c6. These pieces have a potential two-move mating sequence that unguards and re-guards the flight, namely …Rb4-b5, …Bb5-c6, and …Sc6-b4. Black’s rook, e8-bishop, and queen are impeding these mates, and different pairs of these pieces must sacrifice themselves for each sequence to work. 1.Rb4 [A] Rxb4 [a] 2.Bb5 [B] Rxb5 [b]. 1.Bb5 [B] Bxb5 [b] 2.Qc6+ [C] Bxc6 [c]. 1.Qc6+ [C] Sxc6 [c] 2.Rb4 [A] Sxb4 [a]. In the three solutions, Black replays three moves in a cyclic order, AB-BC-CA. White occupies three squares (same as those occupied by Black) in a cyclic order, ab-bc-ca, using changed pieces, and these labels also represent the cyclic captures of three black pieces. The capture of black force is usually incidental in helpmates, but here the effect is thematized in an original way.