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376. Arthur Mosely
Good Companions 1916
Mate in 2

Set mates are provided for all possible black moves: 1…R~ 2.Sd2, 1…Rxd3 2.Qe6, 1…Sb~ 2.Sc5, and 1…Se~ 2.Bxf5. White has no way of retaining all of the set play, e.g. 1.Kb8? Sc6+!, 1.Be6? Rxd3!, while 1.Rc3? (threatening 2.Qe6) fails to 1…Rxd4! The key 1.Qa3! (waiting) grants a flight on d3 but sets up a battery to answer 1…Kxd3 with 2.Sd2. The mate following the correction move 1…Rxd3 is changed to 2.Qxe7. The remaining play is unchanged: 1…R~ 2.Sd2, 1…Sb~ 2.Sc5, and 1…Se~ 2.Bxf5.

Andy Sag: Complete block with one post-key mate change and one added pure mate after flight capture. A try worth mentioning is 1.Kxb7? (2.Sc5) Rb1!, pinning the knight.
George Meldrum: A wonderful key move and after the black king captures the rook, White needs to cover five squares to provide a mating net.
Jacob Hoover: After the key, 1…R~ still allows 2 Sd2 but this time it's an indirect battery play, and the response to the correction 1…Rxd3 (still a self-block) changes to 2.Qxe7. White also has an answer for the flight that the key grants: 1…Kxd3 2 Sd2 (distinct from earlier due to being a direct battery play as opposed to indirect). A rather nice mutate with black correction in both the virtual and actual play.
Ian Shanahan: Fantastic flight-giving zugzwang key. I found this to be most difficult to solve. A concurrent changed-mate after 1…Rxd3. This problem is masterful – just as one would expect from Mosely.

377. George Sphicas
The Problemist 1989
Series-helpmate in 7

The black king could potentially be mated on many squares, but the shortest sequence involves placing it on e2 for a queen mate on c2. This scheme requires Black to promote various pawns to self-block on f1, e1, and f3. Further, since Black is initially in check, the first move has to be a promotion on c1, and the new piece must not interfere with the eventual mate. 1.c1(S) 2.f1(B) 3.e1(R) 4.Ke2 5.d1(Q) 6.Qd5 7.Qf3 Qc2 mate. When first published, this seven-move problem held the economy of length record for a series-helpmate showing the Allumwandlung theme. But subsequently the record of six moves has been achieved, which is the theoretical minimum (given that Black must make four promotion moves plus two queen moves – one diagonal and one orthogonal – to ensure that the queen couldn’t be replaced by another promoted piece). Thanks to Michael McDowell for pointing out the correct source of this problem.

Jacob Hoover: All of the possible promotions (knight, bishop, rook, queen) are seen here, so it's an Allumwandlung.
Andy Sag: A tough one to solve as there are 14 feasible squares for the queen to finish on and c2 was the 8th one I tried. I guess you call it an Allumwandlung as it uses all possible promotions.
Ian Shanahan: Seeing the name above the diagram, one expected the four promotions (AUW, here capture-free). The only blemish is the black king being initially in check, a necessary “trick” to force accurate move-order.

378. Denis Saunders
The Problemist 1990
Mate in 2

The key 1.Se7! concedes a flight on d4 and threatens a battery mate, 2.Rd6. This B + R battery opens twice more with 1…fxe3 2.Rg4 and 1…Rxd4 2.Re6. The e3-knight fires two batteries at once – directly with the e1-rook and indirectly with the f2-bishop – in 1…Sxe5 2.Sc4, and likewise in 1…Kxd4 2.S3f5 but the roles of the rear battery pieces are 
now reversed. There’s by-play with 1…Rxe7/Rd5 2.Qd5 and 1…Qxg6/Qf6/Qe6 2.Qxd3.

Jacob Hoover: With 1.Se7! White activates the B + R battery on the e4-h7 line to go with the R + S battery on the e-file.
Andy Sag: The key gives a flight and threatens a battery mate. The set half battery gives a strong clue. Four variations also involve battery mates, two with double-checks. Try 1.Sg7? Sxe5!
George Meldrum: The setting has enough clues for the savvy solver to find the key. Though the stylishness of the variations is just about enough to do your head in.
Ian Shanahan: Tremendous flight-giving key and a stunning variation after 1…Kxd4. Well constructed too. But very anachronistic for 1990: the Good Companions did this sort of thing, with even greater complexity, 70 years earlier.

379. György Bakcsi
Australian Chess Problem Magazine 1997
Mate in 3

The black king has two flights on d4 and e4, both unprovided. The sacrificial key 1.Sxf4! threatens 2.Sd3+ Qxd3 3.Qxe6. 1…Bxf4 leads to 2.Qxf6+ Ke4+ 3.Qe5 – a cross-check and pin-mate, and 2…Kd6 3.Qe7 – a switchback mate in which the h8-bishop controls e5 upon the removal of the f6-pawn by the queen. If 1…Qxf4 then 2.Qxe6+ Kd4+ 3.Qd6 – another cross-check and pin-mate, and here the e8-rook guards e4 thanks to the queen’s removal of the e6-bishop. And 1…Qe4 allows 2.Qxe6+ Kd4 3.Qc4, and again the e8-rook is activated, this time to cover e5. The flight moves 1…Kd4/Ke4 are answered by the knight threat but a different mate results: 2.Sd3+ Bf4 3.Rxf4. Three times the white queen captures a blocking unit and then opens a line for a white piece, acting as if it’s the front piece of an indirect battery.

Andy Sag: A great feast of pin-mates, cross-checks and indirect batteries.
Jacob Hoover: Indirect battery play in the threat. Direct battery plays by White and Black in the variations, and the white queen performs clearance moves.

380. Robert Lincoln
Australian Chess Problem Magazine 1997
Mate in 2

Initially the black king has three flights, only one of which has a set mate (1…Kd4 2.Qd3). The key 1.Rb3! (waiting) grants a fourth flight on e6 and sacrifices the rook. 1…Ke6 2.Qf5, 1…Kc6 2.Qb7, and 1…Kd4 2.Qd3 together form the Y-flights pattern, while 1…Kc4 also permits 2.Qd3. The remaining variations are as set: 1…S~ 2.Qe4 and 1…c4 2.Qd7. There are plenty of plausible tries: 1.Rc3? (threat: 2.Qd7) Kc6!, 1.Re4? (2.Qd7/Qb7) Kc6!, 1.Qg6? (waiting) Kc4!, and 1.Qe7? (2.Qxc5) Kc6!

Jacob Hoover: The sacrificial key 1.Rb3! completes the block. This problem becomes easy to solve when one realizes that the white rook isn't actually needed to perform any of the set mates.
Andy Sag: Neat miniature with sacrificial key providing for two of the three set flights and adding a fourth. All queen mates from five squares.
George Meldrum: The rook move helps provide for the king flights to c4 and c6. Amazingly no extra solutions are found with so many queen moves to try.
Ian Shanahan: The two unprovided flights really flag the key, but the suite of resulting mates are fine. Theme: three-quarters of a star-flight. There are five distinct variations, in miniature – a form Lincoln used to call a “five bagger”! It's a shame the composer passed away recently.

381. Joseph Heydon
Good Companions 1921
Mate in 2

The key 1.Kxe4!, by controlling d4, threatens mate with any opening of the R + S battery: 2.Sf~. Initially in a safe position, the white king has walked into ten possible checks, and all are met by different mates: 1…Qxe2+ 2.Se3, 1…Qd3+ 2.Sxd3, 1…Qc4+ 2.Qxc4, 1…Qxb4+ 2.Sd4, 1…Qxc6+ 2.Rxc6, 1…Sg3+ 2.Sxg3, 1…Sf2+ 2.Bxf2, 1…Sd6+ 2.Sxd6, 1…Re8+ 2.Se7, and 1…gxf5+ 2.Rxf5. Two non-checking defences prompt white mates already seen: 1…Rd1 2.Sd4 and 1…Rd8 2.Sd6. While the key-move provoking ten checks is impressive, the record for such a task is held by a two-mover by J. C. van Gool, in which the key enables 13 checks.

Andy Sag: The key creates an octuplet threat but invites no fewer than ten checks. Five threats are separated by black moves. Another five defend all threats.
Jacob Hoover: Incredibly, the key 1.Kxe4! invites an ungodly number of checks – ten, in fact! – to threaten a knight discovery on the fifth rank. Five of these checks force particular knight discoveries.
George Meldrum: This problem is one to just simply enjoy.
Ian Shanahan: The check-provoking key is ipso facto excellent, inducing many variations. My only regret is that not all eight threats are separately forced.

Andy Sag proposed to adapt the problem to separate all eight knight mates, and the best setting we came up with is shown below. It accomplishes the knight-wheel task, but at the cost of one of the thematic checking variations.

381b. Joseph Heydon
Good Companions 1921
Version by Andy Sag & Peter Wong
Mate in 2

The same king move now walks into nine black checks, the missing one being 1…gxf5+. We gain three battery variations to complete the knight-wheel: 1…Rg8 2.Sg7, 1…Rh8 2.Sh6, and 1…hxg2 2.Sh4.

382. Nigel Nettheim
The Games and Puzzles Journal 1987
Series-selfmate in 16

Typically in a series-selfmate, White finishes the sequence with a deflecting check that compels Black’s mating move. But here no such white checking move could be made to work, and instead White sets up a position in which the black mate is forced by zugzwang. First White promotes to a knight with the aim of blocking h7, which will cut off the black queen and give the white king access to h6: 1.e5 2.e6 3.e7 4.e8(S) 5.Sc7 6.Se6 7.Sf8 8.Sh7 9.Kh6. White then use the remaining units to self-block on g5 and h5, and at the same time complete the confinement of the black king: 10.Bg5 11.e4 12.e5 13.e6 14.e7 15.e8(B) 16.Bh5. And now Black has only two legal moves, either of which mates: 16…Qxg7/Qxh7.

Jacob Hoover: The idea of this problem is to restrict the movement of both kings and the queen as much as possible. The way to do this involves two underpromotions, one of which is an Excelsior.
Andy Sag: Promotions to queen or rook require the bishop to shield on f8, so any checking finale takes too many moves. A non-checking finale must confine the black king forcing the queen to move, so we have to look for a finale where the queen can mate from either g7 or h7. Checking avoidance by the promoted knight leaves only one route to h7, so well done Nigel!
Ian Shanahan: An elegant miniature with well-motivated move order, particularly in regard to the promoted knight’s wanderings. Whilst White’s non-checking final move is subtle, Black’s dualized mate is a weakness.
George Meldrum: Nigel’s problem is neat and concise, requiring a very methodical move order.

383. Gordon Stuart Green
British Chess Federation Tourney 1954
4th. Hon. Mention
Special British Prize
Mate in 2

Two important set variations are 1…Se5 2.Bxb4 and 1…Sfd4 2.Re3. The thematic key 1.Rxb4! exposes the white king to numerous checks on the long diagonal, and threatens 2.Sd5/Se4 by guarding b3. 1…Se5+ results in a changed mate, 2.Re4, while 1…Scd4+ self-blocks and permits a different opening of the B + R battery: 2.Rb7. The remaining discovered checks by the c6-knight are handled by the threats, and in particular 1…Sxa5+ 2.Sd5 and 1…Sxb4+ 2.Se4 separate them. 1…Sfd4 2.Rb3 shows another change from the set play, and represents a third opening of the white battery. There’s by-play with 1…Sg7 2.Rxg3.

Andy Sag: The key creates a double-threat and sets up an additional battery which comes into play on three occasions, one being a switchback.
Jacob Hoover: Black defends by blocking the c3-h8 line. Two of these defenses (1…Se5 and 1…Scd4) fire the black battery on the long diagonal, a battery play which White counters with more battery play. A third knight defense (1…Sfd4) allows mate by a different double-check.
George Meldrum: The crisscross of play is amazing; the play after 1…Scd4/Se5 is insane.
Ian Shanahan: Cross-checks and batteries à la Mansfield. The key sets up a battery, at the same time opening a black battery directed at the white king. Then… fireworks. Beautiful!

384. Alex Boudantzev
The Problemist 1977
3rd Commendation
Mate in 2

The thematic try 1.Qb4? threatens 2.Qc3 (guarding d3, an unprovided flight). Three variations result: 1…Bd2 (opens the g3-rook’s line) 2.Qc5, 1…Sb5 (self-interference) 2.Qxc4, and 1…Kxd3 2.Qd2 (pin-mate), but 1…Re4! subtly refutes by shutting off the h1-bishop. The key 1.Qf3! threatens 2.Qxe3. A random move by the e3-bishop, 1…B~, enables 2.Qf6 – a changed mate with respect to 1…Bd2 in the virtual play. The correction 1…Bf4 is a self-interference that permits 2.Qe4 (or 1…Re4 2.Qxe4). The flight-move 1…Kxd3 produces a concurrent change, 2.Qd1 – still a pin-mate. Lastly, 1…Re7 is met by 2.Qd5. The correspondence between try and key is striking: the queen on the try-square b4 delivers various mates supported by the a5-bishop and a4-rook, and likewise on the key-square f3 the queen gives mates that require protection by the g3-rook and h1-bishop.

Andy Sag: The key provides for the flight-capture which results in a neat pin-mate.
Jacob Hoover: In all phases of play every mate (including threats) is performed by the queen, so we have the “girl power” theme here too.
Ian Shanahan: The unprovided flight-capture is a blemish, but the idea here – known as the Barnes I theme – is to position the white queen at the intersection point of a white bishop and rook, so it can move along their lines of guard, laterally and diagonally. The try's refutation took time to spot. The pin-mates after the flight are delicious.

385. Peter Wong
feenschach 1995
1st Hon. Mention
Helpmate in 2
Twin (b) Pd3 to b3
(c) Pd3 to a7
(d) Pd3 to d7

The black king on its initial square has too many flights to be covered, so it needs to move to a more confined position. On d4 it could be mated by …Sxe6 – which opens the R + S indirect battery to control the c-file – if e3 is blocked by the queen. But after 1.Kd4?, White lacks a waiting move that would allow this plan to proceed. So Black plays the self-block 1.Qe3 first in order to free the white king to make a tempo move: 1…Kh2!, and then 2.Kd4 Sxe6. Similar tempo strategy occurs in the remaining three parts when the d3-pawn is shifted to other squares: (b) 1.Ra3 Kxf2! 2.Kb4 Sxa6, (c) 1.Rb7 Kg1! 2.Kb6 Sa8, and (d) 1.Se7 Kg3! 2.Kd6 Se8. The four black king moves form a star pattern, while the four white king moves produce a cross.

Andy Sag: Not a twin but a star quadruplet. In each case, Black prepares a self-block and simultaneously allows the white king a tempo move, then the black king moves allowing the c7-knight to mate using an indirect battery to confine the king.
Jacob Hoover: In each solution Black's first move is a distant self-block that also allows White to move the king (because that is the only way White can avoid messing up the configuration of the other pieces). The four white king moves form a king-cross and the four black king moves form a king-star. Very nice. I love it.
Ian Shanahan: Black king star-flight and white king cross. Excellent! Criticism: in each phase, there's a lot of idle ebony.
George Meldrum: The confinement of the white king is not immediately obvious to be part of the main play. The solutions are both amazing and funny at the same time.

386. Cornelius Groeneveld
Australian Chess 2004
Mate in 2

In the diagram, Black’s only mobile unit is the d7-knight and any of its moves would allow 2.Qxc5. White has no way of maintaining this block position, however. The key 1.Qd8! (waiting) prepares an ambush behind that knight and unpins the other one on c5. Now 1…Sd~, besides unguarding b6, enables the queen to control d6 for 2.Sb6. The c5-knight yields two variations: the random move 1…Sc~ admits 2.Qg8 and the correction 1…Se6 prompts 2.Be4. Hence this is a mutate that effects one changed and two added mates.

Andy Sag: A complete block in a Meredith setting. The key unpins the c5-knight and changes the set mate.
Jacob Hoover: The c5-knight exhibits correction play; a random move of this knight loses control of the d5-g8 line while the correction move self-blocks.
George Meldrum: A clinical setting requiring a clinical approach to solving. Positives include: all new mates, delivered by queen, bishop, and knight, not just by the queen as in the set play; a nice key.
Ian Shanahan: A sweet mutate (with only one mate changed) after an unpinning key. The unpinned knight shows secondary black correction.

387. Raimondas Senkus
Australian Chess Problem Magazine 1993
Mate in 2

Random moves by the d4-rook, e7-pawn, and a5-queen lead to these respective mates: 2.Qg1, 2.Sf6, and 2.Qf5. Shifting the white bishop from f4 would threaten 2.Rf4, but White must choose its placement carefully. The first try 1.Bc1? is answered by 1…Rd2!, which cuts off the bishop’s control of f4 while still holding off 2.Qg1 (likewise 1.Bd2? Rxd2!). If 1.Be3? to avoid the black rook’s interception, then 1…Rxe4! refutes since the try-piece has obstructed the set 2.Qg1. The bishop’s try-moves along the other diagonal unguard g5, leaving the h7-knight and c5-queen to control that flight. Consequently, 1.Bh2?/Bb8?/Bc7? all fail to 1..e5! when the set 2.Sf6 no longer works. 1.Bg3? carries a second threat of 2.Rxh4, still playable after 1…e5 or 1…Rxe4, but this try is defeated by 1…hxg3! The last try 1.Be5? directly prevents 1…e5 but interferes with the white queen; now 1…Qd2! cannot be met by the set 2.Qf5. The key 1.Bd6! handles 1…e5 in a new way, by shutting off the black rook, so that 2.Qc8 becomes viable (a changed mate). The initial mate for 1…e5 is transferred to 1…exd6 2.Sf6. The remaining play proceeds as set: 1…Rxe4/Rxd6 2.Qg1 and 1…Qd2 2.Qf5.

Jacob Hoover: The key 1.Bd6! [compared with the tries] can be thought of as a “safety play,” even though it doesn't look so safe. XD
Nigel Nettheim: Nice variations, especially with the e7-pawn.
George Meldrum: A form art in the shape of a parallelogram is seen in the path of white queen as it moves to c8 and g1 and back to the black king. Other lines of play are just colouring in.
Ian Shanahan: It took a little while to work out exactly what the key-piece's destination-square was. A fine problem, with masked interferences.

388. John James O’Keefe
After Jan Smutny
The Australasian Chess Review 1930
Mate in 3

The masked R + B battery on the first rank is only a ruse, and White’s only feasible plan is to use the rook to guard e2 for a bishop mate on that square. A rook try along the b-file, such as 1.Rb8?, is defeated by 1…Bb2!, when 2.Rxb2 stalemates while 2.Re8 fails to 2…Be5. The key 1.Rb4! waits for the black bishop to close a rook-line to e2, whereupon White attacks on that same line, and Black must re-open it due to zugzwang: 1…Bd2 2.Rb2 B~ 3.Be2, and 1…Be3 2.Re4 B~ 3.Be2. After 1…Bb2/Ba3, White plays 2.Re4 again and there’s no defence against 3.Be2. Thanks to Bob Meadley who points out that this problem appeared in the Australasian Chess Review in Forsyth notation only, because of its close resemblance to an earlier three-mover by Jan Smutny. See this article by Bob that features the Smutny precursor and an alternative version of the problem by O’Keefe: Languishing in Forsyth.

Jacob Hoover: In each of the main variations, White paradoxically plays to a line that Black has already blocked and such a play puts Black in zugzwang.
Bob Meadley: A nice three-mover showing the advantages of a rook over a bishop.
George Meldrum: The black king cannot be allowed to move which leads to the rook to be appointed to head the task. A neat interplay between the rook and black bishop.

389. Godfrey Heathcote
The Brisbane Courier 1914-15
5th Hon. Mention
Mate in 2

The black king’s flight-moves to e3 and c2 are both provided, albeit with duals after 1…Kc2. Any white king move that unpins the e4-knight would threaten 2.Sf2, but 1.Kb5/Kb6? fails to either check on the b-file, while 1.Kc7/Kd7? is refuted by 1…Qh7+! Only 1.Kd6! solves – an excellent key that invites four checks. 1…Ke3+ 2.Bd2 (as set) and 1…Kc2+ 2.Bd4 (duals removed) activate the black royal battery on the d-file. 1…g2+ interferes with the h1-bishop, permitting another cross-check, 2.Sg3. And 1…Bxc5+ 2.Sxc5 shows a third opening of the B + S battery. The front pieces of the two white batteries are captured in the by-play: 1…Bxe4 2.Qxe4 and 1…bxc3 2.Raxc3.

Andy Sag: The key unpins the e4-knight but walks into four new checks, two answered by double-checks! I like the g-pawn acting like a valve to shut off the h1-bishop.
Jacob Hoover: Solving this one was rather fun for me (read: cross-checks, yay!). I consider the set-up diagram rather beautiful, because the white units are concentrated on one side of the board and the black units on the other.
Nigel Nettheim: Walking into four checks is great fun! The a1-knight prevents 1.Bc-various+, although a black a4-pawn could have been used instead.
George Meldrum: Stepping through the variations was like walking on water. A very high-quality problem but only gaining 5th Hon. Mention??
Ian Shanahan: A spectacular give-and-take key (unpinning a white piece, but walking into four checks) leads to a lot of cross-check fireworks. It's in typical “Good Companions” style. A fine work by a great problemist.

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

Three thematic defences, aimed at stopping the potential queen mate on f6, generate the set play, 1…Ra6 2.Qe4, 1…Rb6 2.Qd5, and 1…Bf5 2.Qxf5. Various tries threaten the queen mate and lead to the set variations, but are refuted similarly – 1.Rf1? Rf4!, 1.Sh5? Rf4!, and 1.h8(Q)? Rf4! The key-move 1.Se4! (same threat) surprisingly disrupts all three set mates and replaces them thus: 1…Ra6 2.Bb2, 1…Rb6 2.Rc5, and 1…Bf5 2.Qg3. Two more variations complete the play: 1…Rxe4 2.Qxe4 and 1…f5 2.h8(Q).

Andy Sag: The key adds a second guard to d6 and shuts off the a4-rook. Three changed mates noted; how good is that!
Jacob Hoover: A plethora of queen mates is featured in the try 1.Sh5? The key disables the strong defense 1…Rf4 and changes most of the play.
George Meldrum: Centre of attention is on f6 with an array of ways White can focus extra pressure and the threat of mate. Black’s 1…Bf5 sets up the nicest of variations.
Ian Shanahan: Three changed-mates after a rather hard-to-spot key.

391. Geoff Foster
The Problemist 2017
Helpmate in 3
Twin (b) BSe7
(c) BBc6

The diagram is solved by 1.Sd8 Se8 2.Ke6 Ke4 3.Sf7 Bf5. Part (b) with a black knight on e7 instead: 1.Se5+ Kd2 2.Kd4 Bd3 3.Sd5 Se6. And part (c) with a black bishop on c6: 1.Bb4 Kc2 2.Kc4 Se6 3.Bd5 Bd3. The three final positions are all ideal mates. The composer points out that in every solution, the kings make matching moves and each white piece moves exactly once; and further, in (b) and (c) White’s second and third moves are reciprocally changed. A lovely miniature.

Jacob Hoover: A few things each part has in common: (1) one king moves, then the other moves in the same direction; (2) the final position is an ideal mate. Also, in parts (b) and (c) each piece moves exactly once. All this in a very light setting (only six units on the board!). Nice.
Andy Sag: A very economical miniature triplet.

392. Ian Shanahan
Die Schwalbe 2012
Ded. to Eugene Rosner
Mate in 2

The thematic try 1.Rxc4? sets up a masked Q + R battery and threatens a pin-mate, 2.Rd4. The pinning defence 1…Rc5 allows 2.Rxc5, another pin-mate using the same battery. More virtual play occurs with 1…Rc6 (second pinning defence) 2.Bxc6 and 1…Se6 2.Rxf5, but 1…Sf3! refutes. The key 1.Bxf5! creates a masked R + B battery instead, and similar to the try, both the threat 2.Bxe4 and variation 1…Re6 2.Bxe6 show a pin-mate stemming from the battery. Two knight defences demonstrate dual avoidance: 1…Sc5 2.Qxc4 (not 2.Qd2+?) and 1…Sd2 2.Qxd2 (not 2.Qxc4+?). The try play and post-key play involve completely different defences and mates. Such a scheme is called (1) total change when the theme remains the same across the two phases – here masked batteries with pin-mates – and (2) radical change when the theme changes as well – here pinning defences vs. dual avoidance. So both types are effected in this classy two-mover. Note also how 1.Rxc4? Se6 2.Rxf5 and 1.Bxf5! Sc5 2.Qxc4 show reversed captures of the two black pawns and utilise the thematic queen and h5-rook in the phase where they don’t form the masked battery.

Composer: The masked batteries in the thematic try and solution show the Haring 2 Theme.
Andy Sag: The threat and one variation are pin-mates following the key. There are a number of tries, notably the thematic 1.Rxc4?, where the threat and one variation are also pin-mates.
Jacob Hoover: In the diagram, there are two half-pin setups, but there is no half-pin theme here. After the try 1.Rxc4?, two defenses use the e6 and c5 squares: 1…Se6 and 1…Rc5. After the key, defenses at e6 and c5 also appear, but different pieces move to these squares: 1…Re6 and 1…Sc5.
George Meldrum: First choice draws you to 1.Rxc4 which looks compelling but rebuffed. A smile for the clone solution conscious that Ian is sniggering knowing the trek he contrived.

393. Linden Lyons
The Problemist Supplement 2011
Mate in 2

The square-vacating key 1.Ba3! threatens 2.Rb4. Since the rook-check cuts off the bishop’s control of c5, Black can defend by shifting the knight from that potential flight-square. A random move by the piece self-pins the c6-rook: 1…S~ 2.Sd6. The knight has three correction moves that disable the secondary threat of 2.Sd6, but they provoke other mates: 1…Se4 (interferes with the h4-rook) 2.Qd4, 1…Sb7 (interferes with the queen) 2.Sxb6, and 1…Sd3 (self-block) 2.Qa2. The by-play repeats a queen mate: 1…Rd4 2.Qxd4. A well-constructed problem with no white pawns.

Andy Sag: All variations are set; quite easy to solve. The c6-rook is pinned when the knight moves.
Jacob Hoover: The threat is an anticipatory self-interference, so any move of the c5-knight defends due to giving the king a flight-square.
Ian Shanahan: Three nice corrections by the black knight, in ye olde style. The weakness is that the half-pin mechanism is “incomplete”: there are no variations involving the half-pinned rook, leading to a pin-mate with the knight pinned.
George Meldrum: Some nice variations, even if unconcealed.
Nigel Nettheim: Excellent key, excellent play; bravo!

394. Geoff Foster
OzProblems.com 2018
Helpmate in 3
Twin (b) BRf5

The solution of part (a) is 1.Be4 Sc7 2.Kc5 Kc3 3.Bc6 Bd4. Replacing the f5-bishop with a black rook for (b) changes the play to 1.Rc5 Bd4 2.Kd5 Kd3 3.Rc6 Sf4. Two ideal-mates are shown in this neat miniature. The three white pieces make one move each per part, reversing the order in which they play in the two solutions. Although both black pieces starting on f5 self-block on c6, each block cannot go with the other mating pattern.

Composer: In each solution the black piece on f5 takes two moves to get to c6.
Andy Sag: In each case, a black piece moves, a white non-mating piece moves, both kings move, a black piece moves a second time to reach self-block position, and White mates.
Jacob Hoover: In (a) the knight guards empty squares in the king's field and the bishop mates, while in (b) the white knight and bishop swap roles. Interestingly enough, the rook in part (b) ends up on the same square that the black bishop in part (a) ended up on.
George Meldrum: OK, Geoff got me. I solved part (b) but spent a long, long time on the diagram position without finding a solution. A nice miniature setting, damn it!

395. Julius Buchwald
Australasian Chess Review 1942
Mate in 2

Most initial moves by the white king would threaten 2.Bf4, but its placement must be chosen with care. 1.Ke4? is defeated by 1…Qe7!, which pins the bishop and prevents not only the threat but also 2.Bb2, the set mate for 1…Q~. 1.Kf5/Kg5? is similarly thwarted by 1…Qc5! And 1.Kg3? Qd6! sees a third pin of the bishop, this time on a diagonal. The last try 1.Kf3? obstructs a square needed by the d1-knight, so that the self-block 1…bxc2! cannot be answered by a battery mate. The key 1.Kg4! avoids the pins and obstruction: 1…Qb4/Qc5/Qd6/Qe7 2.Bb2 and 1…bxc2 2.Sf3. The original problem was published with a black rook on b2, which I removed because (1) its variation 1…Rxc2 2.Sf3 merely repeats the mate for 1…bxc2, and (2) either capture on c2 foils 1.Kf3?, which is thus lost as a try.

Andy Sag: All king moves besides the key are defeated, mostly by pins; if 1.Kf3? bxc2! (knight can't go to f3) and of course 1.Ke3? has no threat. Also 1.Bd4? and 1.Bc3? are defeated by 1…Qd6+.
Ian Shanahan: The white king has to be careful in choosing the correct destination.
Ata Karayel: The g2-pawn prevents 2.Sg2 after 1…bxc2. 1.Ke4? is countered with 1...Qe7!, an unsettling move.
George Meldrum: An innocuous looking first move providing clear play. The main complexity is demonstrating that other white king moves are not cooks.

396. Johannes Van Dijk
Sydney Morning Herald 1900
Mate in 2

A set line 1…R~ 2.Qxd6 is disrupted by the excellent key 1.Sg3!, which grants two flights and also sacrifices the knight to two black units. The threat is an indirect battery mate, 2.Se2. Captures of the knight permit a pair of queen mates on the long diagonal: 1…Bxg3 2.Qb2 and 1…hxg3 2.Qh8. A third mate on the same diagonal follows one flight-move, 1…Kc3 2.Bf6, while the other king move 1…Ke5 allows 2.Sxc6. All four variations are set up by the key-move (though the non-capturing 1…Bg3 2.Qb2 is prepared) in this clear problem with no by-play.

Andy Sag: The sacrificial key gives two flights. The g6-pawn prevents a dual with the threat if 1…Bc3 but seems to serve no other purpose and could be omitted.
Jacob Hoover: A thematic try is the knight sacrifice 1.Sc3? threatening both 2.Se2 and 2.Sb5. Black can take the knight three ways: 1…Bxc3/bxc3 2.Qf4 and 1…Kxc3 2.Bf6. Unfortunately, 1…Bg3! refutes.
Ata Karayel: Asking about the purpose of h4-pawn solved the problem for me.
George Meldrum: Two flight-squares conceded to the black king; new mates by the knights, bishop, and queen. There is a lot to like in this one.
Ian Shanahan: A sacrificial key giving two flights. Notice too the model mates (after 1…Bxg3 and 1…hxg3). Bravo! A fine problem.

397. John Angus Erskine
The Brisbane Courier 1917
Mate in 3

The key 1.Rb8! concedes a flight on d5 and threatens 2.Sf4+ Kd7 3.Be8. Capturing the d5-knight is exploited as a clearance of the fifth rank in 1…Kxd5 2.Rb5+ (switchback) Ke6 3.Bf5, or 2…Kxc6 3.Be8. Taking the second flight leads to 1…Kd7 2.Bf5+ Kxc6 3.Se7, a model mate. The black rook defends by opening a bishop line to f4, but such moves unguard e4: 1…R~ 2.Re8+ Kxd5 3.Bxe4 – this bishop mate echoes the threat – or 2…Kd7 3.Sb8. Six good mid-board mates including the threat, even though only one is a model.

Andy Sag: The key provides for 1…Kd7 and adds a second flight. Nice variety of play. The position can be simplified a bit by omitting the c1-bishop, as 1…Rf3 is still a defence [subsequently the e2-pawn can also be removed since 1…Re2/Re1 no longer defends].
George Meldrum: The black king has a multiple white square bonanza. The heart and soul of this problem, for me, are the lines involving the knight being captured on d5.

398. Philip O. Pedler
The Australian Problemist 1962
Mate in 2

Initially only 1…Qxg8 and 1…Qe8 are without set mates, and the key 1.Be7! (waiting) completes the block by crossing over f6 so that a knight check on that square wouldn’t cause a self-interference. The black queen’s focus on e5 and f6 is lost in most cases when it moves, e.g. 1…Qh6/Qf7/Qe5/Qxc4 (creating a flight on c6) 2.Se5 and 1…Qxe2/Qd5/Qf6/Qxg8 (creating a flight on e8) 2.Sf6. When the focus is maintained by the queen, new mates result: 1…Qxf5 2.Qxf5, 1…Qxe7 2.dxe7, but 1…Qxd6 allows not only the intended 2.Qxd6 but also 2.Se5/Sf6 due to the pin. The black bishop induces three more mates: 1…Bb6 2.Sxb6, 1…Bc7 2.Rxc7, and 1…Bd8 2.Rxd8. Except for the 1…Qxd6 variation, the play is completely dual-free.

Andy Sag: The key is the only move that completes the block of eight set mates by preventing 1…Qe8 and leaving Black with 17 legal moves. Note the symmetry between ten of the queen moves and knight mates.
Jacob Hoover: The anticritical key 1.Be7! crossing the critical square f6 makes no threat but puts Black in zugzwang. All the set mates are preserved.
George Meldrum: After scanning the board from left to right, we finally come to the key piece. It then moves from the h-file to the e-file, backwards so to speak.
Nigel Nettheim: The key completes the block by ruling out 1...Qe8, so it is perhaps not especially subtle; but the variations are nice.
Ian Shanahan: Here we see the focal theme exhibited by the black queen in action. The element of symmetry detracts somewhat.

Paz Einat and I independently came up with the following correction, which eliminates the triple mate after 1…Qxd6 by making it a check, forcing 2.Qxd6. The original bishop key is replaced by 1.Qd3! Two further advantages of this version are that it saves two pawns and adds three plausible tries – 1.Qf4? Qxe7!, 1.Qf3? Qxd6+!, and 1.Qe5? Qxc4! – a mini duel between the queens.

398b. Philip O. Pedler
The Australian Problemist 1962
Corrected by Paz Einat & Peter Wong
Mate in 2

399. Derek Brummelman
Chess World 1946
2nd Prize
Mate in 2

Every black move in the diagram has a set mate except for 1…Sxe7. The square-vacating key 1.Bb8! threatens 2.Sc7. Since the threat-move cuts off the bishop, any move by the d6-knight would defend by creating a potential flight. The random move 1…Sd~ permits 2.c4. Two correction moves by the piece show subtle dual avoidance. First, 1…Sc4 is a self-block that enables White to self-interfere with the h4-rook, but 2.Sdf4? gives a flight on e4, while 2.Sef4 compensates by opening the e7-rook’s line to the same square. Second, 1…Se4 again self-blocks and now 2.Sef4? fails due to the flight on c4, but 2.Sdf4 works by opening the f1-bishop’s line to that square. The sophisticated line-play rendered – involving white mating moves that simultaneously open and close white lines while exploiting black self-blocks – is known as Theme E. There’s one minor variation, 1…Sd4 2.Rxd4.

Andy Sag: The sacrificial key vacates c7 to threaten 2.Sc7 and thus provide for 1…Sxe7. The main feature seems to be the two self-blocks allowing alternate knights to mate on f4 using indirect batteries to guard the unblocked squares.
Nigel Nettheim: A neat scheme.
Ian Shanahan: A complex tangle of line-openings and -closings involving “valves” and the Russian line-play themes popular in the 1930s. A really fine problem in Meredith!

400. William Whyatt
The Australian Problemist 1963
Place the WK so that White can mate in 2

Regardless of where is the missing king, White has no mate in two if black castling is available as a defence. The placement of the white king is thus aimed at preventing this black move, though not directly, but through retrograde analysis. Add the king on a7, and since a problem position is assumed to have arisen from the normal starting array, we can ask: how did the king get to a7? The black pawns on b7 and c7, which have never moved, preclude a route via a6 or b6. So to reach a7 the white king must have travelled through the 8th rank via d7 or d8, in either case displacing the black king from its starting square. That means the black king has moved previously, and castling is now illegal. The key 1.Qd5! grants two flights on e7 and f8 – or three if castling were legal – and threatens 2.Qxf7, which remains playable after the flight-moves. Two variations follow: 1…Sg5 2.Qd8 and 1…Rf8 2.Qd7.

Andy Sag: White king positions on the 8th rank [a8, b8, and c8] also disable 1…0-0, but are ruled out due to the defence 1.Qd5? Ke7+!
Jacob Hoover: 1…Sg5 interferes with the h4-bishop and 1…Rf8 self-blocks.
George Meldrum: A great fun problem placing the white king. Numerous tries for the two-mover [1.Qxc7? Be7!], and more when you place the white king on c8 [1.Rd7? Rf8!].
Nigel Nettheim: A nice way to present a simple retro idea.
Dennis Hale: An elegant elimination of castling.
Ian Shanahan: A simple yet cute retro!