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

Two set variations of significance are 1…Raxd5 2.Qa4 and 1…Rgxd5 2.Qg4. The key 1.Qxd6! threatens two queen mates that are similar to those in the set play, 2.Qb4/Qf4. Now the rook defences to d5, instead of enabling the queen to mate on the fourth rank, prevent it by pinning the white piece. The rooks have also allowed themselves to be pinned by the white queen, however, resulting in 1…Raxd5 2.Ba7 and 1…Rgxd5 2.Sf5. The black bishop likewise self-pins itself in order to stop both threats: 1…Bxd5 2.Sc6. One further defence occurs on d5, though this knight move does not involve a pin-mate: 1…Sxd5 (or 1…Se6+) 2.Se6. The multiple defences on the same square are enhanced by a pair of changed mates.

Jacob Hoover: Super easy, but all the self-pins made me smile.

277. Cyril Whitehead
Chess in Australia 1985
Mate in 2

A good key 1.Se2! (threat: 2.Sxc3) sacrifices the knight to two pieces and yields a flight on e4. Two knight defences open lines for the white queen to traverse and mate on the long diagonal: 1…Sxe2 2.Qh1 and 1…Sxa4/Sd1 2.Qb7. Another pair of defences open lines of guard controlled by the white rooks: 1…dxe2 2.Se3 (also an indirect battery mate, with the white queen used to attack e4) and 1…Bb4 2.Bc6. Lastly, the flight-move 1…Ke4 is followed by the same bishop mate, 2.Bc6.

Jacob Hoover: I didn't enjoy this one as much as the previous ones, for two reasons: (1) it was very easy, and (2) nothing really stood out to me as a theme.

278. Josif Kricheli
Chess in Australia 1979
1st Place
Helpmate in 2
Twin (b) BSe8

The solution to part (a) is 1.Bxc4 Sf5 2.Bd3 Bg7. The black bishop captures the c4-knight with the aim of clearing the diagonal for the a2-bishop (used to control two flights). The d4-knight directly opens a line for the other white bishop, which mates after it’s unpinned by the black bishop with a switchback to d3. For part (b), a black knight replaces the queen on e8, and the solution becomes 1.Rxd4 Se5 2.Re4 Sg6. Now the black rook removes the d4-knight to activate the c3-bishop (for guarding g7). The c4-knight opens the other white bishop’s line, and it mates after the black rook’s switchback to e4 to interfere with the d3-bishop. The tourney’s judge, Cedric Lytton, wrote: “Line-opening capture switchbacks are beautifully integrated with first an unpin by the black bishop, then an interference by the black rook. Both mates are models, and the pawnless construction is excellent.”

Andy Sag: A tale of two white lines.
Dennis Hale: I remember solving Kricheli's problem in 1979 and being much impressed by it. It was a deserved first-prize winner.

279. Tony Lewis
Australian Chess 2003
Mate in 2

The black king has three flights that together form a ‘Y’ pattern, and white mates are prepared for them: 1…Kxe6 2.Qc8, 1…Ke4 2.Qb1, and 1…Kg5 2.Kc6. Black’s remaining legal move also has a set mate: 1…c6 2.Qe5. Therefore a non-disruptive move by White would solve the problem. Despite the large and mobile white force, only one such waiting move exists – 1.e7!, leaving the set play unchanged. There are many tries, including 1.Rb5? Ke4!, 1.f7?/g7? Kxe6!, 1.Ra4? Kg5!, 1.Kd5? c6+!, 1.Qxc7? Ke4!, 1.Qb2? Kxe6!, and 1.Qb3?/Qd8? c6!

Jacob Hoover: I liked this one for having themes aside from it being a complete block – Y-flights, girl-power, even one battery mate.
Andy Sag: Challenge: how can it be modified to introduce a changed mate?

Although a setting with a changed mate seems unlikely, Andy has produced the following interesting version. The initial position is still a complete block, but there are three set variations only. Now the surprising key 1.Bxg5! (waiting) sacrifices the bishop and generates the fourth variation, 1…Kxg5 2.Kc6. Is such an improved key worth the extra material?

279b. Tony Lewis
Australian Chess 2003
Version by Andy Sag
Mate in 2

280. Nigel Nettheim
The Games and Puzzles Journal 1988
3rd Hon. Mention
Series-selfmate in 12

White aims to place the king on c1 and compel the black bishop to mate on b2 by sacrificing the queen on that square with a check. This plan requires White to use the remaining pieces to self-block on b1, d1, and d2. And when d2 is blocked by the bishop, the only square from which the queen could play to b2 (without already checking Black) is a1. 1.Bb2 2.Sa3 3.0-0-0 4.Qd3 5.Qb1 6.Qa1 7.Kb1 8.Bc1 9.Bd2 10.Kc1 11.Sb1 12.Qb2+ Bxb2. A fine sequence of play that involves castling, switchbacks by the king and knight, and “hesitating” bishop and queen which take more moves to reach their final squares than expected. When this problem was first published, its composer challenged the readers to revise the problem so that it includes promotion. Another difficult task!

Andy Sag: Spotting queen-side castling helps.
Jacob Hoover: I don't usually do this kind of chess problem, but I took this particular one up because it seemed like an interesting challenge, and in that regard it did not disappoint.

281. Herbert Ahues
Chess in Australia 1979
1st Place
Mate in 2

A move by the g4-rook along the rank (to keep controlling e4) would threaten 2.Qf5. Five such moves are thematic tries that fail because the rook would close a vital white line and stop a set mate from working against a black defence. 1.Rh4? Rxh5! (2.Qxh5??), 1.Rf4? Sg3! (2.Qxg3??), 1.Rd4? Rf1! (2.Bb2??), 1.Rgc4? Sd6! (2.R2c5??), and 1.Rb4? Se7! (2.Bd6??). Only 1.Ra4! solves, avoiding the self-interferences and preserving the set variations. 1…Rxh5 2.Qxh5, 1…Sg3 2.Qxg3, 1…Rf1 2.Bb2, 1…Sd6 2.Rc5, and 1…Se7 2.Bd6. There’s by-play with 1…Bxe6 2.Qxe6. The white rook tries exemplify an idea known as “white safety play.”

Andy Sag: This is a try-fest as each defence is related to a try in which other lateral rook moves interfere with one of the intended mates.
Jacob Hoover: A great problem by a great composer.

282. Brian Tomson
Problem Observer 1981
Mate in 2

The bishop check 1…Bxc6+ has a set mate, 2.Bxc6. The key 1.Scxe5! creates a R + S battery on the rank and threatens 2.Se-any (while also yielding a flight on a5). Black’s defences force the white knight to play each of its eight possible moves in turn: 1…Bxc6+ 2.Sxc6 (changed mate), 1…Bd7 2.Sxd7, 1…Bf7 2.Sxf7, 1…Bg6 2.Sxg6, 1…Sc4 2.Sxc4, 1…Rxd3 2.Sxd3, 1…Rf3/Sf3 2.Sxf3, and 1…Sg4 2.Sxg4. A knight-tour is thereby produced. Additional variations are 1…Ka5 2.Sc4, 1…fxe5 2.Rxe5, and 1…c2 2.Qxb4. The thematic try 1.Sdxe5? leads to a similar knight-tour – plus a nice change 1…Kc5 2.Sf3 – and it’s defeated only by 1…c2!, exploiting the unguard of b4.

Andy Sag: Multiple threats separated by defences resulting in a full knight-wheel. Key gives a flight resulting in a required double check.
Jacob Hoover: This puzzle was enjoyable enough with the knight-wheel battery play, but the changed mate is also a nice touch.

283. Vyacheslav Antipov
Australian Chess Problem Magazine 1993
Mate in 3

The natural tries 1.Rg1/Rg2? (threats: 2.R7g5, etc.) are defeated by 1…d2! followed by a queen promotion. If 1.Re7?, aiming for 2.Re3/Re1, then again 1…d2! refutes. The key 1.Rd7! creates no threat but waits for each black pawn to make a weakening move. 1…f4 2.Re5 and 3.Re8. 1…d2 2.Rxd2 and 3.Rh2. 1…c3 2.Rxd3 and 3.Rh3.

Andy Sag: A miniature three-move waiter.
Nigel Nettheim: Technically the c4-pawn is not needed for soundness, but it makes the key less obvious and adds a variation. Easy to solve but certainly neat.
Jacob Hoover: An excellent miniature chock full of strategic play.

284. Arthur Ford Mackenzie
The Sydney Morning Herald 1899
3rd Hon. Mention
Mate in 2

White’s royal battery is prepared to fire in response to many black moves, but there are no set mates against defences such as 1…Ke5, 1…Ra~file, and 1…Re~rank. The key 1.Qg7! (waiting) creates another battery on the long diagonal and completes the block. 1…Sb3/Sxd3+ 2.Kb3, 1…Sc2/Sxc4+ 2.Kc2, 1…Sxa2 2.Kxa2, 1…Sxb1 2.Kxb1, 1…Ra~rank 2.Kxa3, 1…Re~file 2.Kxc1, 1…Ra~file/Sb5/b5 2.Se4, 1…Re~rank/Se2 2.Sd5, and 1…Ke5 2.d4. Quite symmetrical but this is an impressive way to achieve four related pairs of variations, all involving battery play. Note also the changed mates with respect to two tries: 1.Qc6? 1…Ra~file 2.Qd5 and 1…Re~rank 2.Qe4, but 1…Ke5!; 1.d7? 1…Ra~file 2.Qd6/d8(Q) and 1…Re~rank 2.Qf4, but 1…Se2! The dual in the latter try is removed after 1…Ra8, so a 3x2 Zagoruiko is shown, though probably not intended.

Andy Sag: The white king moves are the same after 1…Sb3/Sxd3+ or 1…Sc2/Sxc4+, but the situation is different as in one case the knight must be captured and in the other case the knight gives check but need not be captured as it has pinned itself. Five symmetrical pairs of battery variations including pin-mates after the checks. Wow!
Jacob Hoover: The 1…b5 2.Se4 line is a change from the set 1…b5 2.Qc5. I found this problem exceptionally pleasing, what with all the battery play and even two cross-checks.
Nigel Nettheim: The symmetry, which suggests the key, is the main attraction. The composer had been blind for several years.

285. Frederick Hawes &
Frank Ravenscroft

Chess Life 1958
Mate in 3

If White advances the king to protect the c7-pawn, then 2.Rd8 will be threatened. But it would be premature to play 1.Kb6? (additional threat: 2.Bb7) bxc4+!, 1.Kc6? Rxd3! (not 1…Sb4+? 2.Qxb4 and 3.Rd8/Qf8), or 1.Kd6? g2+/Rxd3+! Instead White plays the sacrificial 1.Qc3! with a short threat, 2.Qh8. Note that although the key obstructs 1…Rxd3, 2.Kc6? is still not threatened because of 2…Sb4+. Now three black defences enable White to play each of the king moves as a continuation. 1…Rxc3 2.Kb6 and the two threats are separated by 2…Rxd3 3.Bb7 and 2…Qg2/Qh1 3.Rd8. 1…Sxc3 2.Kc6 and 3.Rd8. And 1…Qb2 2.Kd6 and 3.Rd8. The original threat is extended to a full-length variation with 1…Qh6/Qh5/Qf2 2.Qh8+ Qf8/Qe8/Qf8 3.Qxf8/Qxe8/Qxf8.

Nigel Nettheim: Very nice control of the white king’s advance. The a3-rook prevents both 1.Rd8+ Kxc7 2.Qa5 mate and 1.Qc3 Qb2 2.Kd6 Qa3+. It’s nice to see a directmate where Black has the superior force.
Andy Sag: The short mate threat is a bit untidy.
Jacob Hoover: Enjoyable problem from the collective genius of Hawes and Ravenscroft.

286. Frederic Lazard
Queensland Chess Association 1920
Mate in 2

The initial position is a complete block, with white mates prepared against all possible black moves. Tries by the white king fail to black checks: 1.Kg5? Se6+!, 1.Kh4? Sf5+!, 1.Kf3? Qxf7+! Only 1.Kh3! (waiting) works, retaining all of the set play. 1…Qxf7 2.e8(S), 1…Qxf8 2.exf8(Q), 1…Qxd8 2.exd8(S), 1…Qxe7 2.Bxe7, 1…Sg~ 2.fxe8(S), 1…Bxb7 2.c8(S), 1…Rxb8 2.cxb8(Q), and 1…Sa~ 2.bxc8(S). A promotion extravaganza in which four white pawns deliver seven mates by promoting to a queen or a knight. Furthermore, the units in the diagram form the letter ‘T’, making this is a striking shape problem (which can even be improved – see Nigel’s delightful version below).

Andy Sag: Eight variations, seven involving promotions including three symmetrical pairs.
Jacob Hoover: It's been a while since the last complete block problem, and this one was quite good.
Nigel Nettheim: The position is very nicely blocked. Moving the g4-king to h7 would make the set position even more picturesque, and the key (1.Kh8!) would still be quite attractive.

287. Laimons Mangalis
Chess Life 1957
Gamage Memorial Tourney
3rd Prize
Mate in 3

In this intricate three-mover, the key 1.Sb1! threatens 2.Sa3+ bxa3 3.Qc3/Qxb3. The black rooks defend by playing to d3, and in doing so also form a half-pin on the third rank. After 1…R4d3, 2.Qxe2 pins the rook to threaten 3.Sd6, and if 1…Bg3, then the f3-bishop – which was self-pinned by the queen move – gets unpinned for 3.Bd5. Likewise, after 1…R1d3, 2.Bxe2 pins the rook to threaten 3.Sd2, and now 1…Sf3 unpins the queen that was just self-pinned by the bishop move, allowing 3.Qc1. A third defence on d3, 1…Sd3, interferes with the d1-rook and is a self-block as well: 2.Qxd4+ Sxd4 3.Sd6. The unguard 1…Rxb1 admits 2.Bxd4 with two threats separated by 2…Bg3 3.Bd5 and 2…Sc~ 3.Sd6. Lastly, 1…Sc2 is followed by a dual, 2.Qxe2+/Bxe2+, and in either case 2…R4d3 3.Sd6 and 2…R1d3 3.Sd2. A rich strategic problem, featuring an anticipatory half-pin of two white pieces.

Andy Sag: A tough one to solve. It is all about disrupting Black’s control of the d-file by diverting, pinning and/or disconnecting the rooks.
Jacob Hoover: This was a difficult one.
Nigel Nettheim: The doubled rooks defend well, so White disrupts them in various ways. The e2-pawn seems unneeded.

288. Niharendu Sikdar
Australian Chess 2005
Mate in 2
2 solutions

In both solutions the white queen unguards c4 so that the black king has access to all four of its diagonal flights. After the first key 1.Qe7! (waiting), each flight-move is answered by a different mate: 1…Ka4 2.Qxb4, 1…Kxa6 2.Bf1, 1…Kc4 2.Qe2, and 1…Kc6 2.Sd4. The second key, 1.Qd8! (waiting), completely changes the responses to the four king moves: 1…Ka4 2.Qa5, 1…Kxa6 2.Qb6, 1…Kc4 2.Bf1 (transferred mate), and 1…Kc6 2.Sc3. An excellent doubling of the star-flights theme, accomplished in a light setting.

Andy Sag: A good example of star flights.
Thomas Thannheiser: Interesting mate changes between the two solutions.
Jacob Hoover: The 1…Kc4 and 1…Kxa6 defences switch mating pieces between the solutions. Particularly in the 1…Kc4 variations, the white queen and bishop swap roles in guarding the d5-knight and giving mate. An unusual problem, and easy as well, but it was a great one.
Nigel Nettheim: Stellar.

289. Godfrey Heathcote
Sydney Morning Herald 1909
Mate in 2

A random move by the c6-knight would threaten 2.Qb7, but 1…Sf4! refutes. The correction 1.Sxe7? answers 1…Sf4 with 2.Rfe3, but then Black has 1…Sxe7+! The key 1.Sd4! again covers f5 and leads to the same battery variation, 1…Sf4 2.Rfe3. The fine key also concedes a flight and unpins the c4-pawn, which is freed to give two discovered checks. Three more battery variations result: 1…Kd5 2.Rf5, 1…cxd3+ 2.Rf7, and 1…c3+ 2.Sb3. And if Black captures the key-piece with 1…exd4, then 2.Rxd4.

Jacob Hoover: The key sets up a potential battery on the fourth rank. Both 1…Sf4 and 1…cxd3+ are self-blocks, while 1…Kd5 2.Rf5 is a pin-mate!
Nigel Nettheim: Nearly a knight-wheel of tries. The knights are the star performers.

290. Andrew Dempster
Chess in Australia 1987
Helpmate in 5

The diagram position nicely displays perfect symmetry between the white and black forces. 1.Kg7 Kb2 2.Kf6 Kc3 3.Ke5 d4+ 4.Kd5 Kd3 5.Sd6 Sb4. The two kings march towards each other to set up an ideal-mate in the middle of the board. Simple play but a good miniature find.

Nigel Nettheim: The set position is attractive. The kings come out from their corners to fight in the centre of the ring; the result is a fifth-round knockout.

291. Arthur Mosely
Good Companions 1923
2nd Prize
Mate in 2

White mates are prepared against all legal black moves in the diagram: 1…R~ 2.R3b4, 1…Rc4 2.Sf5, and 1…e3 2.Be5. Tries that attempt to preserve all of the set play include 1.Kg5? g6! and 1.Kxg7? Ra7+!, while 1.Rh5? leads to the change 1…Rc4 2.Sb5, but it’s refuted by 1…e3! The key 1.Bd2! (waiting) instead changes the response to the pawn move, 1…e3 2.Bxc3, and adds the variation, 1…cxd2 2.Se2. The black rook correction play is retained: 1…R~ 2.R3b4 and 1…Rc4 2.Sf5. A tricky mutate with a surprising key that sacrifices the bishop.

Nigel Nettheim: The changed mate after 1...e3 still acts on the long diagonal.
Jacob Hoover: 1…Rc4 and 1…e3 are self-blocks. Quite the clever block-mutate, with some black correction play thrown in for some added flavour.

292. Kazimierz Grabowski
The Brisbane Courier 1903
1st Prize
Mate in 2

After the square-vacating key 1.Bf3!, White threatens 2.Qe4. Black has four defences that are self-blocks, and White exploits them in a harmonious way: 1…Sxd6 2.Sc6, 1…Sf6 2.S8f7, 1…Bf5 2.S6f7, and 1…Qd4/Sd4 2.Sc4. In each case, the mating knight interferes with a white line-piece that was guarding a flight-square, now obstructed by the defending black piece. The remaining variations show black self-interferences: 1…Sc3 2.d4, 1…Sg3 2.Qf4, and 1…Rg4 2.Rf5. This striking strategic problem is even more remarkable considering its early publication date.

Andy Sag: Threat plus seven variations, most involving self-blocks or defensive line interference.
Jacob Hoover: Quite a nice problem, with a clear theme (self-interferences) that has no distracting by-play.
Nigel Nettheim: The key and threat are not hard to find, but the play is really excellent. The g7-pawn is not needed, with the white king on b8.

293. Peter Wong
The Problemist 2002
Shortest proof game in 16

The quickest way to reach the diagram is 1.f4 a5 2.f5 a4 3.f6 a3 4.fxg7 Sf6 5.gxf8(B) Rg8 6.Bh6 Rg3 7.Bg7 Rb3 8.axb3 a2 9.Bf8 Ra3 10.bxa3 Kxf8 11.Bb2 Kg7 12.Qc1 Kg8 13.Kd1 Sh5 14.Bf6 Kf8 15.Qb2 Ke8 16.Kc1 axb1(R)+. The promoted white bishop executes a three-move manoeuvre to lose a tempo, after which it is captured by the black king. The latter then also makes a tempo trek to use up three moves in a precise way. Both White and Black’s treks begin and end on f8. This doubling of the tempo play is combined with the Frolkin theme (capture of a promoted piece).

Andy Sag: Waiting move by White’s bishop and black king triangulation are necessary to get the tempo right.

294. Leonid Makaronez
Australasian Chess 2010
Mate in 3

The unexpected key 1.Rb6! (waiting) leads to two thematic variations: 1…cxb6 2.Rc4 Ke2 3.Rc1 and 1…c6 2.Bc4 Kc2/Kc1 3.Be2. Black’s c-pawn is kept immobilised as the c5-rook and b5-bishop interfere with each other on c4 – producing a white Grimshaw – to release the black king. The latter is forced by zugzwang to shift to a more exposed position and White mates by opening the battery formed by each Grimshaw move. The by-play makes further use of the key-piece: 1…cxd6 2.Bd3 and 3.Rb1.

Nigel Nettheim: A Grimshaw-like theme with reversed colours: not Black but White takes advantage of the mutual interferences on c4, to avoid stalemate. There are good tries and a wonderful key. I found this very hard to solve but well worth-while.
Jacob Hoover: Very difficult; kept me stumped for days.
Andy Sag: A precise lightweight setting by the Israeli master.

Michael McDowell informs us that this problem is anticipated: “The Makaronez three-mover rang a bell. It adds a variation to the attached Shinkman. I remember solving this one in a newspaper column when I was about 12 or 13!” The precursor seen below gives the same thematic play, and its sacrificial key by an unrestricted rook (1.Ra6!) is even better.

William Shinkman
Caissa’s Ghost 1890
Mate in 3

295. Joseph Heydon
Good Companions 1920
Mate in 2

White begins with 1.e4!, which cuts off the f3-bishop and threatens various battery mates, 2.K~. The key is also thematic in that it opens the third rank and enables the black queen and bishop pair to check. Each possible bishop move is answered by a different opening of the K + R battery: 1...Bxe4+ 2.Kxe4, 1…Be2+ 2.Kxe2, 1…Bd1+ 2.Kc4, and 1…Bxg4+ 2.Kc2. So along with a duel between the black bishop and the white king, the problem shows a king-star. Minor variations include 1…Rxf2 2.Bxg3, 1…c5 2.Qd5, and 1…Sxg6/Se6 2.Qe6.

Andy Sag: The key interferes with the long white-square diagonal and creates a quadruple threat.
Jacob Hoover: No mates are prepared for 1…Bd5 or 1…axb4; White remedies this by playing 1.e4! and it activates the black Q + B battery.
Nigel Nettheim: The key counters the strong defence 1…c5. The multiple threats do not matter, because they are nicely separated into a star pattern.

296. John Lindsay Beale
Check! 1944
Mate in 2

After 1.Bf2!, White threatens 2.exd4 and Black defends by moving the e5-knight, which opens a line for the bishop on h8. 1…Sf7 interferes with the other black bishop and permits 2.Rc1. 1…Sc4 again cuts off the bishop and also self-blocks, enabling 2.Sb3. A similar pair of variations occurs when the knight obstructs the h6-rook twice: 1…Sg6 2.Qb6 and 1…Sc6 2.Sa6 – the latter is a self-block as well. The fifth defence by the knight is yet another interference: 1…Sg4 2.Sxe4. The by-play consists of 1…dxe3 2.Bxe3, 1…Rd6 2.Qb5, and 1…Rb6 2.Qxb6.

Andy Sag: The five knight defences produce five black line interferences and two self-blocks, and 1…Rd6 adds another self-block.
Nigel Nettheim: The e1-bishop and g1-rook had to take part, so the key was easy to find. The theme is a partial black knight-wheel. The g8-bishop prevents 1.Bd5 (2.Sb3).
George Meldrum: The knight on e5 does cartwheels providing a pleasing variety of mates. Variations great; key move rather ordinary.
Jacob Hoover: All of the main variations except for 1…Sf7 2.Rc1 are set. A nice illustration of line play.

297. Michal Dragoun
Australian Chess Problem Magazine 1992
Helpmate in 2
Twin (b) Kd3 to e5

The solution to part (a) is 1.Bd2 Bd4 2.Rg6 Bf5. Black starts with a self-blocking bishop move that also clears the long diagonal for the white bishop, which goes to d4 to control the e3-flight and unpin the black rook. The latter then opens the d-file for the white rook (to guard the d4-bishop) and interferes with the h7-bishop, allowing the second white bishop to mate. Part (b), with the black king starting on e5, is solved by 1.Rf6 Rd4 2.Bb4 Sc4. Now the black rook self-blocks and permits its white counterpart to get to d4, where it covers two more flights and unpins the c3-bishop. This bishop then opens a line for the white one on a1 (to guard the d4-rook) and cuts off the black queen, enabling the white knight to mate. A well-constructed orthogonal-diagonal transformation, showing perfect analogy between the two parts.

Andy Sag: Good twin with self-block, unpin, black line self-interference, mate sequence in each case.
Jacob Hoover: This was quite difficult, but once I understood what was going on in the first part, the second part was very easy.

298. James Joseph Glynn
The Australian Chess Annual 1896
Mate in 2

The key 1.Bf1! (waiting) creates a B + P battery and completes the block. The c3-rook produces four variations: 1…Rd3 2.exd3, 1…Re3 2.Sxe3, 1…Rf3 2.exf3 and 1…Rg3/Rh3 2.e3. The latter mate also follows 1…cxd1(S), exploiting the half-pin, while 1…cxd1(Q) admits 2.Rxc3. Basic correction play is seen in 1…Q~ 2.Qb5, 1…Qxb6+ 2.Sxb6 and 1…Bf~ 2.Qxc3, 1…Bxe5+ 2.Sxe5. The remaining defences are unguards: 1…Rb~ 2.Sb2, 1…Be~ 2.Qd5, 1…Sb~ 2.Qc5, 1…fxg6 2.Qxe6, and 1…a4 2.Rb4. Straightforward play and the position is super-heavy (using almost the full chess set!), but justified by the great number of variations, all dual-free.

Andy Sag: Waiter with fourteen variations!! Eleven are set and the key sets up a battery to deal with the rest.
Jacob Hoover: Quite easy to solve due to the fact that the g2-bishop is the only white unit not participating in the action. But it was also a rewarding solve at the same time.
Nigel Nettheim: Very nice and elaborate. The black f6-bishop had to be promoted, because it could not have escaped from f8; thus it is an intrusive piece. The position is legal, although it is not quite trivial to establish that. The only missing units are four white pawns and two black pawns. The f6-bishop must have been promoted on a black square, which could have been c1, with either of the black pawns starting on c7 or d7 (in either case, White’s c-pawn was captured). The e4-pawn must have captured a piece promoted on h1. Thus the position is legal.

299. Ladislav Salai Sr.
Australian Chess Problem Magazine 1997
Mate in 2

The black king has two flights, both provided: 1…Kxe4 2.Qe2 and 1…Kd3 2.Qf3. If White aims to preserve these variations with a waiting move – 1.Ke6?, for instance – then 1…b4! refutes. The key 1.Bd1! involves two threats, 2.Qf3 and 2.Qe2, which are separated by 1…Kxe4 2.Qf3 and 1…Kd3 2.Qe2. These variations demonstrate a reciprocal change with respect to the set play, by reversing the two queen mates. Note also the paradoxical elements: in the set play, 1…Kxe4 enables 2.Qe2 and 1…Kd3 enables 2.Qf3, but after the key, 1…Kxe4 disables the threat of 2.Qe2 and 1…Kd3 disables the threat of 2.Qf3.

Nigel Nettheim: Two threats, but the point is the changed mates.
Jacob Hoover: Too easy! The king's moves separate the threats; and a miniature to boot.
Andy Sag: An interesting miniature. The b5-pawn appears not to contribute but without it there would be eight solutions!

300. Jens Kieffer-Olsen
Chess in Australia 1982
Mate in 3

The key 1.fxg6 e.p.! is legal if we could prove by retro-analysis that Black’s only possible last move was …g7-g5+. In the initial position, White is missing only the b-pawn, which was captured by Black’s pawn on b6. With no other white units to capture, Black’s f-pawn must have moved straight down the file to f2. This means White’s f5-pawn needed to have captured to get around the black one, and the four white pawns on the king side have made a total of three captures (e.g. fxg, gxf, gxh). These three captures account for all of Black’s missing pieces (queen, rook, and bishop).

Since Black is checking with the g5-pawn, it has just moved from f6, g6, or g7. This last move couldn’t have been …f6xg5+, however, because of the lack of spare white units to capture. If Black has just played …g6-g5+, what was White’s move before that? It couldn’t have been:
• Qg5-g4, Se7-g8, or Sf6-g8 because Black would have been in check with White to play;
• Sxg8 since Black’s missing pieces were all captured by the white pawns;
• Kg5-h4 as that must be preceded by …g7xh6+, again an impossible black capture;
• d3xe4 because that would imply too many white pawn captures had taken place (five in total);
• g2xh3 because an uncaptured queen or rook on h3 would have been checking White with no way of delivering that check, while the third missing black piece is a black-squared bishop which couldn’t have reached h3 to be captured.

Hence we have shown that …g6-g5+ would mean an illegal position with no further white retraction possible. That leaves …g7-g5+ as the only possible last move, prior to which White had played Bg6-h7 or Qg6-g4. So White can play 1.fxg6 e.p.!, with the short threat of 2.Rf8. 1…Sxf4 2.Qc8+ Kxc8 3.Sf6, and 1…Bxg4 2.Sf6+ Ke7 3.Re8. Some duals follow other black defences, e.g. 1…exf4 2.Qc8+/Sf6+.

Andy Sag: The main issue is the need to establish that black's previous move was …g7-g5+ thus enabling the en passant key.
Jacob Hoover: This is the first chess problem I have seen on this blog where White is in check in the diagrammed position. And it was also a moderately difficult solve.
George Meldrum: Very nice.