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.

If the white queen adds a guard on f4, that will threaten 2.Rg6, though 1.Qc1? is thwarted by 1…Sd2! The key 1.Qxc7!, with the same threat, triggers two pairs of thematic variations. In the first pair, Black’s queen and b6-bishop pin the white rook, but they cause a mutual interference: 1…Qd4 2.Se3 and 1…Bd4 2.Qf4. In the second pair, Black’s queen and b7-bishop cut off the white bishop (creating a potential flight on f5), but they also interfere with each other: 1...Qe4 2.f3 and 1…Be4 (pinning the white queen) 2.Rf4. The subsidiary line 1…e5 2.Qd7 further utilises the white queen, and 1…Bxc7/Be3 2.Se3 repeats a main variation mate. The standard Grimshaw theme employs a rook and a bishop that close each other’s line; here a pinned black queen takes the place of the rook, and the idea is doubled. The dual avoidances after 1…Bd4 and 1…Be4 – each pinning a different white piece – are especially pleasing, while 1…Qd4 and 1…Qe4 result in pin-mates.

George Meldrum: A barrage of new lines after the key. Love the pin on the white queen after 1…Be4 preventing a dual by stopping 2.Qf4 mate.

White’s mainplan is to shift the bishop along the path Be8-h5-g4 to mate. However, 1.Be8? fails to 1…Bc3 2.Bh5 Bf6+ (or 1…Ba5 2.Bh5 Bd8+). White must first implement a foreplan designed to neutralise that black bishop. 1.Bb5! threatens Bxe2-g4, against which 1…Bc3 is ineffective – 2.Bxe2 Bf6+ 3.Kh5 ~ 4.Bg4. 1…c4 is a weak defence since 2.Bxc4 carries a second threat on e6, forcing 2…Bd5 3.Bxe2 ~ 4.Bg4. The thematic defence 1…Sc3 obstructs the e1-bishop as planned, but 2.Be8? is still premature because the black knight can now counter with 2…Sd5 3.Bh5 Sf6. Another foreplan is required to neutralise the knight. 2.Bd7 threatens 3.Bxe6, and 2…Bd5 blocks the square that the knight wants to access. The mainplan 3.Be8 threatening Bh5-g4 is finally playable, and the new defence 3…e5 (4.Bh5? Be6) permits 4.Bd7+ Be6 5.Bxe6. White can’t switch the order of the two foreplans for a subtle reason. 1.Bd7? Bd5 2.Bb5 and if 2…Sc3? then 3.Be8 works by transposing to the main line, but here 2…c4! refutes as the pawn is protected by the black bishop.

George Meldrum: There looks to be other ways to achieve this, but only 1.Bb5 works.
Bob Meadley: Nice square blocker.

To mate the black king on its original square proves impracticable, e.g. 1.Bb3 Ra1 2.Rxe4 Ra5 is hampered by the queen, even though both flights on e4 and e5 are dealt with. The two solutions begin with flight-captures on these e-file squares, which help to bring the white rook and bishop into play. After 1.Kxe4, the potential mate …Rf4 cuts off the h6-bishop, so White wants to guard not only e5 but also e3 with a knight move. 1…Sxc4? does the job but deprives Black of a self-blocker for d5, leaving the poor option 2.Rd5 which inadvertently opens a line for the queen and disrupts the mate on f4. Thus 1…Sg4 is necessary for 2.Bd5 Rf4.

These dual avoidance effects by both sides (1…Sxc4? and 2.Rd5?) are perfectly matched in the second solution, which commences with 1.Kxe5. Now the potential mate …Bf4 cuts off the f1-rook, so the remaining knight should guard both e4 and f5. But 1…Sxd6? removes a self-blocker for d5, forcing the poor alternative 2.Bd5 which opens the rank for the a4-rook and prevents the mate on f4. White must choose 1…Sg3 to facilitate 2.Rd5 Bf4. The orthogonal-diagonal transformation involves two doubly-masked black lines to f4, and even includes a white Grimshaw on that square. The construction is flawless, giving an economical Meredith setting with no plugs (pure cook-stoppers) at all.

Andrew Buchanan: Different roles for different units, and dual elimination (white knight destination on 1st move, black piece to self-block on 2nd move). Queen instead of bishop on b8 eliminates cooks.
George Meldrum: Superb.