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426. Andrej Lobusov
Chess in Australia 1981
Mate in 2

The black king has a flight-move to e5, answered by a triple, 2.Sb7/Sc4/Sf7 (curiously these mates all recur individually in subsequent play). Both the try and the key by the e5-rook remove that flight but grant a new one, besides activating the half-battery on the dark diagonal. The thematic try 1.Rxe3? threatens 2.Qf2 and leads to 1…Kxe3 2.Sdf5, 1…dxe3 2.Sb7, 1…Ra1 2.Sc4, and 1…Sxd3/Se4/Sxe6 2.Re4. But 1…g4! refutes, as the set mate 2.Rf5 for this defence is no longer possible. The key 1.Rxg5!, with the threat of 2.Qxh4, brings about some attractive changes relative to the try play: 1…Kxg5 2.Sf7 (new flight and mate), 1…Sxg5 2.Sb7 (transferred mate), and 1…Ra1 2.Se4 (changed mate).

Andy Sag: The half battery gives a strong clue to the give-and-take key. Very nice changes!
Jacob Hoover: There are three defences after the key, and each one forces the B + S battery to fire in a different way. A proliferation of battery plays (one of which is indirect) and no distracting by-play.
Ian Shanahan: A lovely sacrificial, flight-giving key from the half-battery. There is a symmetrical try and threat, defeated by 1…g4! Grandmaster Lobusov was working on spectacular keys and battery play at the time.

427. Gordon Stuart Green
The Problemist 1970
Jubilee Tourney
1st Prize
Mate in 3

If Black were to begin, every legal move has an immediate mating response set: 1…f2 2.Se2, 1…S~ 2.Qe5, and 1…B~ 2.Qf2/Qh2. With no waiting move that could maintain all of these variations, White must play a key that extends the solution to three moves, making this an example of a pseudo two-mover. The excellent key 1.Sh3! changes the replies to two black defences and also adds two more variations, by granting a flight on h4 and sacrificing the knight. After 1…f2, White answers with the threat-move 2.Sxf2, which leaves Black in zugzwang: 2…B~ 3.Rfg1, 2…Bxe4!? (correction move) 3.Sxe4, and 2…S~ 3.Qe5. Since 2.Sxf2! acts like the key of a two-mover, generating three precise variations, this problem also exemplifies an insert two-mover. The second change is 1…S~ 2.Sf4 and 3.Sxh5, or 1…Sf6 2.Sf4 (waiting) 2…S~ 3.Sxh5, 2…f2 3.Se2, 2…B~ 3.Qf2/Qh2/Rfg1. Black taking the flight leads to 1…Kxh4 2.Sf4+ Kg5 3.Rxh5, 2…Kg3 3.Sxh5. Or if Black accepts the sacrifice: 1…gxh3 2.Rhg1+ Kxh4/Kh2 3.Sxf3. Lastly, the set dual is removed in 1…B~ 2.Qf2. This difficult problem was placed first in a tourney for three-movers that are either pseudo or insert two-movers, but it manages to combine the two ideas.

Andy Sag: Sacrificial flight-giving key with a waiting move threat. First time I've seen that!
George Meldrum: Amazing.

428. Abdelaziz Onkoud
Australian Chess Problem Magazine 1995
Mate in 2

Set mates are prepared for most of Black’s moves in the diagram, except for 1…dxe6 and 1…Se2. The key 1.Bd3! (waiting) completes the block by providing for these two defences and it also adds two variations by unpinning the d4-pawn. If this pawn captures either rook, White exploits the opened d-file: 1…dxe3 2.Bf5 and 1…dxc3 2.Bb5. The key-bishop mates directly after the self-blocks, 1…dxe6 2.Be4 and 1…dxc6 2.Bc4. The remaining defences are mostly unguards: 1…f5 2.Re5, 1…b5 2.Rc5, 1…cxd6 (self-block) 2.Sxb6, 1…S8~ 2.Sxf6, 1…a3 2.Qb3, 1…Sf3 2.Qxf3, and 1…Se2 (line-opening) 2.Qh1. A total of eleven variations, including eight pawn defences.

Andy Sag: The key unpins the d4-pawn, removes the set mate 1…d3 2.Qxd3 but adds four mates making eleven variations including five symmetrical pairs, the highlight being the pair of battery mates after each rook is captured!
Jacob Hoover: Tries 1.Be2/Bb5/Ba6? dxe6! and 1.e7/exd7? Se2! An easy but nonetheless rewarding solve, as the variations display multiple themes (battery plays, self-blocks enabling white self-interference).
George Meldrum: Eleven ways to checkmate, and although many are in set play the new added mates are outstanding.
Ian Shanahan: An incomplete-block. 1…Se2 has no mate set for it, which points to the key piece (if not its destination). A waiter in ye olde style, with a fine sacrificial key that eliminates the set variation 1…d3 2.Qxd3.

429. Henryk Grudziński
Australian Chess 2007
Helpmate in 2
Twin (b) Ka4 to d6

The first part is solved by 1.Rb2 Rf3 2.Sb4 Bxb5. The black rook unblocks a flight in order to unguard the eventual mating square b5 (without closing prospective white lines: 1.Rc4/Rb3?). The white rook prepares an attack behind the d3-knight, which then opens lines simultaneously for both white pieces. The knight also blocks the square that was vacated by the black rook and interferes with the latter’s control of b5. The white rook is thus allowed to guard two flights while the white bishop traverses the opened line to give mate. The second part has the black king starting on d6, which changes the solution to 1.e5 Bg4 2.Se7 Rxf6. Now the black pawn creates a flight on e7 and unguards the mating square f6, while also self-blocking e5. After the white bishop is placed behind the f5-knight, the latter opens lines for both white pieces and blocks the square vacated by the e-pawn, besides cutting off the e8-rook. With the white bishop activated to observe the d7-flight, the white rook mates by moving along the opened line.

Jacob Hoover: In each part a black unit moves in order to enable a black knight to perform a necessary self-interference; also, the white rook and bishop exchange functions between the two parts.
George Meldrum: A single black knight move plugs a flight square, blocks a defence, and opens lines for White’s bishop and rook, in both versions.
Andy Sag: Rook and bishop take turns in guarding escape squares while the other piece mates, after a knight clears lines as well as self-blocking. The f6-pawn appears to be unnecessary apart from ensuring the mate involves a pawn capture.
Nigel Nettheim: The exchange of roles of the two white pieces is nice, although only about half the black units take part in each twin. Easy to solve.
Michael McDowell: What is the idea of the problem? A black knight replaces an ineffective self-blocker, while the white rook and bishop exchange functions, taking turns to guard flights by ambushing behind a knight, or mate by moving along a vacated line. Unfortunately the strategy is mismatched. The only task of the b4 rook is to unguard b5, and it chooses b2 to avoid closing a line which White needs open. The e7-pawn must unguard f6, but e5 must be blocked, so its move has a second purpose. The self-block 2.Sb4 happens to interfere with the b2-rook, so the composer added a rook at e8 to create the impression of matching interferences. Helpmate composers call this sort of piece a weasel – the rook is superfluous and is unnecessary for soundness. Because a pawn at b5 is needed to shield the white king the composer added a pawn at f6 simply in order to have matching captures on the mating moves. This pawn is also superfluous. A lighter and more harmonious problem could be created by replacing the black square vacations with self-blocking moves which move across the squares which the knights will then block.

Michael McDowell
(after H. Grudziński)
OzProblems.com 2019
Helpmate in 2
Twin (b) Ka4 to c1

(a) 1.Ba3 Re5 2.Sb4 Bb3.
(b) 1.Rb2 Bh7 2.Sd2 Re1.

430. Johannes Van Dijk
The Brisbane Courier 1925
4th Hon. Mention
Mate in 2

Initially, Black’s only mobile unit is the knight and it produces a set variation, 1…Sh6/Sh8 2.Re8. The amazing key 1.Sb2! (waiting) cuts off the two white pieces on the a-file and concedes five flights to the black king. Four of the flight-moves lead to battery mates, though all king moves to the second rank are answered similarly: 1…Kxd4 2.Sbd1 and 1…Kd2/Ke2/Kxf2 2.Sc4. The last king defence admits a queen mate: 1…Kf4 2.Qc1. The black knight’s moves let the f8-rook control f4 and enable the key-piece to deliver an indirect battery mate: 1…S~ 2.Sbd1 (a change from the set play).

Jacob Hoover: The key seems counter-intuitive, since not only does it prepare no threat, it also grants no less than five flights!
Andy Sag: Tries 1.Sxb4? Se5!, 1.Rxf7?? (stalemate). Classic star-flight waiter with pure mates after king moves to the f-file.
Nigel Nettheim: White’s force is so overwhelming that flight-giving was likely; five is generous.
George Meldrum: This problem is hilarious, in a good way.
Ian Shanahan: A spectacular waiting key, creating a double battery to deal with the flights. It's a pity that mating moves are repeated.

431. Joseph Heydon
Australasian Chess Magazine 1920
Mate in 2

The key 1.g4! unpins the e6-rook and threatens 2.Rb6. Black has four pawn defences that unpin the white queen, which then mates in a variety of ways. The en passant captures re-pin the white rook, but open lines for the queen: 1…hxg3 e.p. 2.Qh5 and 1…fxg3 e.p. 2.Qf5. More line-openings occur with 1…e3 2.Qd5 and 1…c3 2.Qe2. The by-play consists of 1…Be3 2.Sc3, 1…Sxe6 2.Bxd7, and 1…Qc6 2.Bxc6/Re5/Sd6. This remarkable task problem – achieving four black pawn unpins of the white queen – came about as an answer to a challenge set by the great Alain C. White, who had produced a similar setting earlier. See J.K. Heydon: Problemist, Solicitor, Businessman, No.46, for the full story, including White’s version of the task.

Andy Sag: A pinned pinner setting! The key unpins the rook on e6. All four pawn defences give different pin-mates by the unpinned queen.
Jacob Hoover: Incidentally, the four white queen mates are all pin-mates, which lend a degree of unity to the problem.
Andrew Buchanan: En passant! Pity that 1…Qc6 allows three new mates.
Nigel Nettheim: The unpin 1…Be3 (and the non-variation 1…Bc3) suggests an e.p. capture in the reverse direction, increasing the appearance of unity, although that unpinning is not essential to the following mate.
Ian Shanahan: The central idea is “pawns unpinning by interference”. The only flaw is the ugly triple after 1…Qc6; otherwise, a fine problem by a composer who died too young.

432. George Meldrum
OzProblems.com 2019
Mate in 3

This difficult three-mover commences with the sacrifice 1.Rxe4! which grants the black king a second diagonal flight, besides the one on g6. Surprisingly the key entails no threat but waits for Black to make a self-weakening move. 1…Kxe4 is met by the brilliant 2.Qxf3+, yielding 2…Kxf3 3.Bd5, 2…Kf5 3.Qd3, and 2…Kd4 3.Sb3 (pin-mate), where the three king moves form the Y-flights pattern. If Black plays 1…Kxg6, then 2.Re7 threatens 3.Bh7, which isn’t stopped by 2…Kf5, thanks to the removal of the g6-pawn. Any black rook move allows the a1-bishop to control e5 and f6, freeing up the g4-knight: 1…R~ 2.Bh7 (threatens 2.g7/Sf6, both battery mates) Kxe4 3.Sf6 (now an indirect battery mate), 2…Rb2 3.g7, and 2…Se5 3.Rxe5. Lastly, 1…S~ prompts 2.Re5+ Kxg6 3.Rg5. Excellent play that combines spectacular sacrifices with subtle white second moves (1…Kxg6 2.Re7 and 1…R~ 2.Bh7) that are hard to find.

Composer: While it is possible to remove the bishop at a1, rook at b2, pawns at c2 and c5, the problem holds up and removes the double threats [after 1…R~ 2.Bh7]. Still I like their inclusion to give that extra complexity.
Andy Sag: The major double sacrifice makes this problem very difficult to solve. Good one George!

433. Vladimir Kuzmichev
Chess in Australia 1991
Mate in 2

The key-move 1.Bh8! is a Bristol clearance (of maximum possible length) that allows the queen to follow the bishop along the long diagonal. The threat of 2.Qf6 is stopped by three of the black king’s four legal moves. Although 1…Kh6 and 1…Kg6 are answered by the same thematic queen move 2.Qg7, these are distinct variations that produce different model mates. Another model occurs with 1…Kf4 2.Qc1. The fourth king move 1…Kh4 doesn’t deal with the threat, but it’s still a pity that a second mate is possible: 2.Qf6/Bf6. Arguably, if Black obligingly plays 1…Bxe4, then the threat 2.Qf6 becomes a model as well! Note the tries 1.Bg7? Kg6!, 1.Qa6? Bc6!, and 1.Qa5+? Bd5! The latter is perhaps the most interesting because it generates two changed mates relative to the actual play: 1…Kh6 2.Qh5 (yet another model!) and 1…Kg6 2.Qh5 (an echo of the post-key threatened mate).

Andy Sag: A miniature with an obvious Bristol clearance key which maintains the four set flights (two unprovided).
Jacob Hoover: All of the mates after the king’s moves are pure mates, and this lends a degree of unity to the problem.
Nigel Nettheim: Although there’s a dual after 1…Kh4 and the black bishop doesn’t take part in the play, the long key-move is nice and partial star-flights are present.
George Meldrum: Predictive key but pleasing, nonetheless. Black’s king is mated on five different squares. Not bad for such a lightweight setting.
Andrew Buchanan: Major dual, and unprovided black half-pin distract from elegant model mates. Instead of the a8-bishop one could economize with a d7-pawn; still get all the tries.
Ian Shanahan: There are unprovided flights, and the white queen is badly out-of-play. The clearance-to-the-corner key veritably leaps to the eye. Some nice mates ensue.

434. Alex Boudantzev
The Problemist 1974
Mate in 2

The thematic try 1.Rc2? is a Novotny move that cuts off two black line-pieces to threaten 2.Sdc4 and 2.Qe4. The threats are separated by 1…Bxc2 2.Sdc4 and 1…Rxc2 2.Qe4, and there’s more virtual play with 1…Sf4 2.Qf6, but the try is defeated by 1…Rf4! The key 1.Sc2! is another Novotny double-interference and though it occurs on the same square, one of the generated threats is different: 2.Rc5 and 2.Qe4. The normal mate separation follows with 1…Bxc2 2.Rc5 and 1…Rxc2 2.Qe4. The first-rate key also gives two flights to the black king, leading to 1…Kd5 2.Qd4 and 1…Kf5 2.Qf6. As in the try play, 1…Sf4 answers both threats but a new mate results: 2.Qg5. This fine piece of work was surprisingly unplaced in its Problemist informal tourney.

Andy Sag: A flight-giving Novotny key with unavoidable double-threat, two pin-mates [2.Qe4 and 2.Qg5] and one changed mate.
Jacob Hoover: 1…Kf5 2.Qf6 is a transferred mate [relative to 1…Sf4 2.Qf6 in the try play].
Nigel Nettheim: The key blocks two intersecting lines (Novotny). A thematic try (1.Rc2?) and a changed mate (1…Sf4) are good features. The flights are too, even if their mates are not elegant.
George Meldrum: The queen mates in mirror-like fashion for the black king flights.
Ian Shanahan: A fantastic Novotny key, yielding two flights. There’s also a mate changed after 1…Sf4. Superb problem!

435. Geoff Foster
Yves Tallec-80 Jubilee Tourney 2008
1st Hon. Mention
Helpmate in 6
Twin (b) Swap Sb3 and Sc4

The diagram position is solved by 1.Kd3 Kc1 2.Kc3 Kd1 3.Kb2 Sd4 4.Ka1 Kc2 5.Sa3+ Kb3 6.Sb1 Sc2. The white king traces a curious triangular path to b3, while the black knight avoids the dual 5.Sd2? as it would prevent 5…Kb3. The twin (b) begins with the black king in check, and this fixes the order of Black’s first two moves in the solution: 1.Kd4 Kc2 2.Sc1 Kd1 3.Kc3 Sa5 4.Kb2 Kd2! 5.Ka1 Kc2 6.Sa2 Sb3. Here the white knight must not play 3…Sd2? because that would obstruct the square needed by the white king for the tempo move, 4…Kd2! Good interplay between White and Black in this helpmate showing exact echoes of an ideal-mate.

Andy Sag: Nice twin. The white king must lose two tempos to allow the black king to reach a1 in four moves and the black knight to get to b1 and a2 respectively in two moves to self-block.
Jacob Hoover: Clearly the black king must be mated in a corner, as White doesn't have enough material to achieve mate anywhere else. In part (a) the choice of the square Black moves the knight to must be made carefully (5.Sd2?), while in (b) the white knight must choose its square carefully (3…Sd2?).
Nigel Nettheim: Very nice indeed!
George Meldrum: I really like the solution to the (b) flipside. In vinyl record terms, this is a double A-side hit.

436. Frederick Gamage &
Eric Hassberg

Chess World 1946
3rd Hon. Mention
Mate in 2

The corner-to-corner key 1.Qh8! threatens 2.Qxb8. Defences by Black’s queen and bishop on the a-file leave each other pinned by the white rook, a weakness exploited by White in the battery variations, 1…Qf8 2.Rf7 and 1…Be8 2.Rd7, where the b7-rook shuts off each defender in turn. The half-pin is utilised again in 1…Qe7+ 2.Rxe7, another battery mate. The by-play 1…Qd6 2.Rxa4 produces a fourth pin-mate.

Jacob Hoover: The black queen and a4-bishop are half-pinned; if one moves the other will be pinned.
Andy Sag: The half-pin on the a-file, the long diagonal battery and the far away queen suggest a long-range pinning key. Most Gamage problems involve pins and unpins.
George Meldrum: Classic corner-to-corner key for a cornered king problem.
Nigel Nettheim: A half-pin is shown very succinctly.
Bob Meadley: Very lightweight for Gamage.
Ian Shanahan: The key is obvious and strong (also because the white queen is initially out-of-play), but it leads to some fine half-pin play involving shut-offs. A good Meredith (8 to 12 units).

437. Joseph Wainwright
The Brisbane Courier 1919
Mate in 3

If the white bishop controls c3 with either 1.Ba5? or 1.Bd4? to threaten 2.Sc5, the flight-move 1…Ke4! is too strong. The key 1.Bxe3! aims for 2.Bd4 (removing the e4-flight) followed by 3.Sc5, and if the unpinned black knight checks, that prompts two good sub-variations in the threat: 2…Sb6+ 3.Bxb6 (switchback) and 2…Sf6+ 3.Bxf6. Black’s pawns on c6 and e6 can defend by observing d4, but these moves have the drawback of unguarding the d5-knight. After 1…c5, 2.Bh6 surprisingly puts Black in zugzwang: 2…e5 3.Rxd5 and 2…c4 3.Bb1, exploiting a self-block. White answers 1…e5 with the same waiting move 2.Bh6, and while 2…c5 3.Rxd5 repeats a mate, 2…e4 3.Rd2 involves a different self-block with a pleasing break from symmetry. Finally, the flight-move 1…Ke4 permits 2.Bb1+ Ke5 3.Rxe6.

Jacob Hoover: White has no set continuation prepared for 1…Ke4 (or for any other black move, for that matter) in the diagrammed position, so it seems that the key should be a move designed to keep the black king from escaping via f4.
Andy Sag: Black has only five legal moves. The unpin of the black knight on second move allowing checks livens it up.
George Meldrum: The black king should be prevented from reaching the f-file. This makes finding the key a little easier. Did not see Bh6 coming but it did provide a pleasant surprise.

438. Denis Saunders
The Problemist Supplement 2003
Mate in 2

Most of Black’s moves in the diagram are provided with set mates, other than 1…R~file. Two waiting tries prepare for these rook moves. The first 1.g6? vacates g5 for 1…R~ 2.Seg5, but 1…Rh5! keeps an eye on the mating square. The second 1.d7? attacks e5 by discovery, effecting a changed mate, 1…R~file 2.Qxe5, but because the try-pawn has cut off the c8-bishop, 1…Rxg5! cannot be met by 2.Sexg5. The sacrificial key 1.Qc3! (waiting) controls e5 directly. 1…R~ 2.Qxe5, 1…Rxg5 2.Sexg5, 1…B~/Sa~ 2.Sc5, 1…Se~ 2.Sd2, 1…d4 2.Qc6, and 1…d2 2.Qc2. This problem is a precursor to the same composer’s No.248, a twin setting that he considered far superior. Nevertheless, this is a worthwhile version with two good tries and a changed mate.

Jacob Hoover: An incomplete block with some changed mates between the try- and actual phases.
Ian Shanahan: A triply sacrificial waiting key to a problem composed in a 19th-century style.
George Meldrum: This whimsical problem sees the queen being fed to the horses and bishop yet Black can no longer escape via his castle.