Weekly Problems 2015-B

The key 1.Sc7! observes e6 to threaten 2.Qc5. The half-pin arrangement on the fifth rank is unusual in that the thematic black units – the f5-pawn and the g5-knight – are also the front pieces of batteries aimed at the white king. When either black unit defends by giving a discovered check, the other is left pinned, a weakness that White then exploits: 1…f4+ 2.exd3 and 1…Sg~+ 2.Sxg4. Three secondary variations are: 1…c3 2.Sxd3, 1…Be4/Rxg3 2.Qxd4, and 1…Sxc7/Sf6 2.Qf6.

Jacob Hoover: Beautiful. I enjoyed the 1…f4+ 2.exd3 line in particular, due to it involving a battery mate in response to a battery check.

Set play is arranged for the black king’s two possible moves: 1…Ke3 2.Sf4 Ke4 3.Re2 and 1…Kd5 2.Bg2. Despite the freedom of White’s overwhelming force, there’s no waiting move that could retain both set variations. The surprising key 1.Rc1! (waiting) changes the continuation after 1…Ke3 to 2.Sf2, followed by the sub-variations 2…Kxf2 3.Bd4 and 2…Kd2 3.Bf4. The short mate 1…Kd5 2.Bg2 is unchanged. A three-move mutate that’s tougher to solve than it looks!

Jacob Hoover: Eureka! 2…Kxf2 3.Bd4 is a model mate.

The key 1.Sg5! threatens 2.Se4, against which Black has three unified defences on the same square. These moves to g3 unpin the e5-rook and enable White to fire the Q + R battery. In each case, the black move has an additional effect that compels the white rook to land on a particular square on the e-file. 1…g3 opens the fourth rank: 2.Re4; 1…Rg3 controls the third rank: 2.Re3, and 1…Sg3 opens the first rank: 2.Re1. The white rook is unpinned a fourth time with 1…Sd6 2.Rf5, which exploits the new guard of e7 by the a7-rook. There’s plenty of by-play in this impressive battery problem: 1…Sc5 2.Rxf7, 1…Bxe5+ 2.Qxe5, 1…Qxg5 2.Bxg5, and 1…gxh6 2.h8=Q.

Nigel Nettheim: The black pawn on a5 can be removed.
Jacob Hoover: What I liked about this problem is the multitude of themes illustrated (unpins, line-opening, and line-closing) and that the e5-rook, despite being pinned in the diagram, is the mating unit in four out of the eight variations. Masterful.

Back in 1988 I proposed a tourney idea for Chess in Australia, in which every piece of a problem position must stand on its game-array square. This highly restrictive condition did not generate a sufficient number of entries for a tourney, but of the few examples that appeared, I liked Andy’s helpmate best. The solution is 1.Qc8 Sf3 2.Kd8 Se5 3.Kc7 Bf4 4.Kb8 Sc6. White sets up a battery to give a double-check model mate. The position is economical (nearly a miniature) with most pieces taking part in the play directly – only the d7-pawn is used as a plug to stop a dual.

White prepares an indirect battery on the b-file with 1.Qb8! (waiting). The key also changes the direction from which the queen controls b5, so that the potential mate Sc5 would not cause a self-interference. Now a random black queen move, 1…Q~, unpins the b3-knight and admits 2.Sc5. The correction move 1…Qxa3 self-blocks and leads to 2.Sc3 (when the white queen is needed to guard b4). Also, 1…Qxb3+ 2.cxb3. The black knight also enacts correction play; the random 1…S~ opens a white bishop line and allows 2.Sc3, while 1…Sd5 defends c3 but frees the b3-knight for 2.Sc5. The two pairs of thematic variations produce a reciprocal effect – the two white knights swap their roles in responding to Black’s random and correction moves.

Jacob Hoover: Note that if 1…Qxc2, the queen will be pinned by the d1-bishop after the knight moves. A lovely problem with a nice reciprocal theme seen with the knight mates.

A fine waiting key, 1.Qb1!, relinquishes the Q + S battery and gives the black king an additional flight. The three diagonal flight-moves produce 1…Kxc6 2.Qb7 – a switchback, 1…Kc4 Qd3 – a pin-mate, and 1…Kxe6 2.Bf7. Unusual for a multiple-flights problem, there are many good supplementary variations: 1…S~ 2.Qxe4, 1…Be~ 2.Rxd6, 1…Bd~ 2.Qa2, and 1…dxe6/dxc6 2.Qa2.

Jacob Hoover: Many variations deal with line-opening. Nothing really noteworthy about this problem aside from the plethora of queen mates, in my opinion.
Nigel Nettheim: Flights to 3/4 of a star (thus a thematic key); the captures by Black make up – or more than make up – for the star being not complete. Efficiently constructed with some very nice mates.

If White protects the h3-knight with an additional piece, the g1-knight would be freed to give mate. This plan prompts two plausible tries and the key. The first try 1.Ke4? threatens 2.Kf4/Kf3 3.Kg4 and 4.Sf3. After 1…Bg5 (which answers 2.Kf3? with 2…Bxe3 3.Kg4 Bxg1), White continues with 2.Sxg5 Kxg1 3.Sf3+ Kf2/Kf1 4.Rb2. But Black cleverly escapes with a self-immobilising manoeuvre, 1…Bh4! 2.Kf4/Kf3 g5 3.Kg4 – stalemate! The second try 1.Bb7? threatens 2.Bf3 3.Bg4 and 4.Sf3. The stalemate defence wouldn’t work here because of the unblocked a-pawn, but now 1…Bg5! is effective because of 2.Bf3 Bxe3 3.Bg4 Bxg1 or 2.Sxg5 Kxg1 3.Sf3+ Kf2/Kf1. The key 1.Ke2! threatens 2.Kf3 3.Kg4 and 4.Sf3. If 1…Bh4 then 2.Rg5 forces 2…Bxg5 3.Sxg5 Kxg1 4.Sf3, a mate that relies on the white king’s position on e2 to control f2 and f1.

Jim Cannon indicates that the program Fritz 12 was unable to find this problem’s key, managing only to mate in five moves. But Jim’s son David Cannon (a top junior player) solved it successfully!

After the square-vacating key 1.Sc5!, White threatens 2.Re4. Black has two pairs of defences on e6 and b4, where each couple results in a mutual interference between two line-pieces: 1…Be6 2.Sc6, 1…Re6 Rxd5, 1…Bb4 2.Sb3, and 1…Rb4 2.Qxc3. Thus the Grimshaw theme is presented twice. The white queen does more work in the by-play, 1…Rd6 2.Qh4 and 1…Sd2/Sg3 2.Qxe3. Also, 1…Rg4 2.Sc6 and 1…Rxd7 2.Sb3. Most other moves by the key-piece contain multiple threats (e.g. 1.Sg5? threatens 2.Re4/Sf3/Qh4), but these are tries that fail to provide for 1…Bb4! And if 1.Sd2? to answer 1…Bb4 with 2.Sb3, then 1…Rb4! refutes since 2.Qxc3 is disabled.

Jacob Hoover: Not just one, but two pairs of Grimshaw interferences.
Nigel Nettheim: The mutual interferences on b4 and again on e6 are very nice.

The first part is solved by a waiting key, 1.Qxd3!, which offers the queen to both black knights. 1…Sf~ self-pins the f3-pawn and enables 2.Se2, while 1…Sb~ allows 2.Sd5. The black rook shows correction play: 1…R~ 2.Qxf5 and 1…Rxh5+ 2.Sfxh5, the latter an indirect battery mate. The two black pawn moves both open a line for the queen: 1…e2 2.Qd2 and 1…e4 2.Qd6. In part (b), the key 1.Sh7! involves a threat, 2.Bxg5. Now defences by the f2-knight are followed by a different mate: 1…Sh3/Se4 2.Qe4, which exploits the white rook’s pin of another f-pawn. More changed mates occur when Black moves the rook: 1…R~ 2.Rxf5 and 1…Rxh5+ 2.Sgxh5. Three good free changes are brought about in the two phases of play.

Jacob Hoover: Quite interesting that the pin is featured in both parts, but in different ways.
Nigel Nettheim: In (a), the capturing key is fine; the queen needs access to d2 and d6. In (b), the try 1.Sfe4? is well answered by 1…Sh3! Remarkably, both parts seem to be efficiently constructed.

The B + S battery on the long diagonal seems prepared to fire if Black captures one of the eight white units constraining the e5-knight, e.g. 1…Bxf3+ 2.Sxf3 and 1…Rxg4+ 2.Sxg4. But there is no set response to 1…Sxd3 or 1…Sxc4, where each defence removes a white pawn needed to control a flight. The key 1.Sb6! threatens 2.Sd7 and also guards c4 and d5; now 1…Sxd3 2.Sxd3 and 1…Sxc4 2.Sxc4 are possible. Five other capture defences are answered by the set battery mates – all return captures by the e5-knight. 1…Sxc6 2.Sxc6, 1…Rxf7 2.Sxf7, 1…Rxg6 2.Sxg6, 1…Rxg4+ 2.Sxg4, and 1…Bxf3+ 2.Bxf3. Together with the threat-move, these white mates complete a knight-tour that is well unified by the square clearance effects. There’s by-play with 1…dxe5 2.Bxe5, and a try 1.Sf8? (threats: 2.Sd7/Se6) Sxc4!

Composer: The eight moves of the knight represent the orbit of the Earth around the Sun. The black king, like the Sun it represents, is eccentric or not placed in the centre of the circle.
Nigel Nettheim: A satisfying complete cycle traced out by the e5-knight.
Jacob Hoover: This knight-wheel is just awesome in that, going anti-clockwise from the threat square, the thematic defences include first three knight moves, then a bishop move, then three rook moves. Very orderly.

The key 1.Rc6! threatens 2.Qc3. Since the threat entails the queen unguarding e3, any move of the rook on that square would defend by creating a potential flight. A random rook move – effectively what would occur if the piece is simply lifted off the square – allows two possible mates, 2.Sce2 and 2.Qf4, and they are differentiated with 1…Re2/Rf3 2.Se2 and 1…Rxg3 2.Qf4. Three corrections by the rook prevent these secondary threats but allow other mates, due to the arrival effects of the rook: 1…Re4 2.Sf5, 1…Re5 2.Bb6, and 1…Re6 2.dxe6. The black queen initiates three variations, all based on unguards: 1…Qa3/Qc4 2.Rc4, 1…Qb3 2.Sxb3, and 1…Qb4 2.Qxb4.

Jacob Hoover: Square-clearing key, while the rook defences grant the black king a flight square.
Nigel Nettheim: The defences by the e3-rook and by the queen are handled with nice variety and no duals. The a5-rook might seem unneeded, but it prevents a dual after 1…Qa5.

Helpmates in which the black king moves to another square to be mated are often tricky to solve. Such is the case here, as the black king walks into a double-pin model mate in each solution: 1.f4 Sb3+ 2.Ke3 Rh3 and 1.Re6 Re2 2.Ke5 Sc6. That the pins are all constructed in the course of play, rather than pre-existing in the diagram, is considered an important feature. White’s knight, bishop, and h2-rook all change their roles in the two parts, acting variously as a guard, pinner or mating piece, though we don’t see an interchange of functions between any two pieces.

The key 1.d7! threatens 2.d8=Q and allows Black to check on the rank. White activates the Q + B battery on the g-file when the black rook interferes with b7-bishop: 1…Rd5 2.Be5 and 1…Rc6+ 2.Bf6. The b7-bishop cuts off the black rook in turn with 1…Bc6 2.Rc8, producing a Grimshaw. Another interference occurs in 1…Re5 2.Sf6, while the same mate results from 1…Bf6 2.Sxf6. Lastly 1…Bxg7+ forces 2.Qxg7, a variation that makes good economical use of the white queen.

Jacob Hoover: I found the many self-interferences appealing (especially the Grimshaw pair) but the repeated mate (2.Sf6) I didn't like very much.
Nigel Nettheim: Very neat play, including Grimshaw interferences on c6 and single interferences on d5 and e5.

White mates are prepared against all possible black moves in the initial position. 1…Se~ opens the first rank and permits 2.Qb1, while the correction 1…Sc2 is a self-block that leads to a white self-interference mate, 2.Sb2. Any black bishop move enables the white rook to control e2: 1…B~ 2.Qxe2. Yet another line-opening error is committed by Black in 1…e3 2.Qf5. And 1…Sb~ is an unguard that allows 2.Sc5. White has many tries that aim to preserve the set play, but they are refuted thus: 1.Ke8? Sd6+!, 1.Ke7? Bg5+!, 1.B~? Bh6+!, and 1.Rb2? Sc2! Only 1.Kg8! works, a waiting move that retains all of the set variations.

Jacob Hoover: The key utilises the only square the king can move to where he can't be immediately checked.
Nigel Nettheim: It is amusing that the white king simply dodges checking defences; it is set on its optimal square, immobilizing the white bishop.

White could aim for a rook mate on h8 by opening the top rank, but such moves by the king are defeated if played immediately: 1.Kc7? Rxc4+!, 1.Kxd7? Qxd4+!, and 1.Ke7? Rxe5+! The superb key 1.Qd1! shows a triple sacrifice, and it threatens 2.g5+ fxg5 3.Bxg5. Black’s major pieces are decoyed in the variations, 1…Rcxd1 2.Kc7 and 3.Rh8, 1…Rexd1 2.Ke7 and 3.Rh8, and 1…Qe2 2.Kxd7 and 3.Rh8. If 1…Qxd1, the black queen loses control of the half-battery on the h-file, admitting 2.Bg5+ fxg5 3.Sg1. The half-battery operates again in 1…Re2 2.Bg5+ fxg5 3.Sf2. There’s by-play with 1…f3 2.Qxd2+ Re3 3.Qxe3, when the white queen dispatches two of its own capturers from the main variations!

Nigel Nettheim: An amazing key, controlling h5 for the threat and, more importantly, overloading the black pieces.
Jacob Hoover: A highly unified problem.

An excellent key, 1.Sc4!, sacrifices the knight and yields two flights to the black king. The threat of 2.Qc6 is answered by the h4-bishop in two thematic variations, 1…Bf6 2.Sg5 and 1…Be7+ 2.Sd6. In each case the bishop interferes with a pinned rook that could potentially defuse the B + S battery, allowing White to unpin the piece with impunity when opening the battery with the knight, which needs to re-guard the e4-flight. The battery fires again if Black accepts the sacrifice – 1…Kxc4 2.Se5, while taking the other flight leads to 1…Ke4 2.Qxf5. Lastly, 1…Rd6 2.Sxd6 shows a mate similar to that in one of the main variations. The late Brian Tomson remarked when this problem was first published, “A sophisticated two-mover.”

Nigel Nettheim: The key must be made with the d6-knight, but its destination is determined with intricacy. A highlight is the cross-check after 1…Be7+.
Jacob Hoover: Another problem that involves my favourite chess problem theme – battery play.

A nice withdrawal key 1.Be8! threatens 2.Bg6. The white queen, initially pinned by its counterpart on the long diagonal, is freed remarkably five times to give various mates. Three such unpins occur by interposition: 1…Sc3 2.Qe3, 1…c3 2.Qxd5, and 1…d4 2.Qg3. The rest are direct unpins by the black queen: 1…Qb6 2.Qf5 and 1…Qxe2 2.Qxe2. The two queens share one more variation in 1…Qd4 2.Qxd4. Lastly, the g4-knight delivers two mates in the by-play, 1…Qxe5+ 2.Sxe5 and 1…Sg5/Sf4/Sf2 2.Sf2.

Jacob Hoover: Several black defences unpin the queen.
Dennis Hale: At first glance, 1…Qb6 seems to defeat 1.Be8; it defends both g6 and e3 and hence prevents 2.Qe3, but White has 2.Qf5. It is a nice symmetry that the key and its threat involve a long forward move (1.Be8) and a long backward move (2.Bg6), and the most promising defence and its aim involve a long forward move (1…Qb6) and a long backward move (2…Qe3).
Nigel Nettheim: Good, if not truly memorable. The h2-pawn prepares 1.Bxb2? hxg1=Q!; the g2-pawn then disarms 1…h1=Q after 1.Be8!

The black king has four accessible squares initially, and intricate play is required to organise a mate that covers all of these flights. In part (a), White plans for a bishop mate on f5, which necessitates support from the white king and a clearance capture by a black piece: 1.Sf4 Ke7 2.Se3 Kxf6 3.Sxf5 Bxf5. After a self-block on f4, Black uses the c4-knight (rather than the h5-bishop) for capturing on f5, so as to allow the white rook to guard d4. Part (b) has a black queen starting on g6, and the resulting solution shows an orthogonal-diagonal transformation of the strategy seen previously: 1.Se5+ Kxd6 2.Qg1 Kc5 3.Qxd4+ Rxd4. The rook mate on d4 motivates the white king’s different approaching moves. Black’s self-block on e5 is followed by the queen’s clearance capture on d4, which also helps the white bishop to control f5. The two white line-pieces therefore exchange their roles in the two parts, and so do the black pieces on c4 and g6, although curiously the identity of the g6-piece is different in each case.

In this complete block position, white mates are arranged for all possible black moves: 1…Kxc5 2.Qd6, 1…Sb~ 2.Rc4, 1…Sg~ 2.Qf2, and 1…Se3 2.Qe5. But White has no simple waiting move that could maintain all of these set variations. After 1.Qd2! (waiting), the queen loses control of e5 and d6 but attacks c3 and is also ready to support the d-pawn. Now three of the four variations involve changed mates: 1…Kxc5 2.d4, 1…Sb~ 2.Rd5, 1…Sg~ 2.Qf2, and 1…Se3 2.Qc3. This mutate has two good tries that show more changed play: 1.Sd1? 1…Sg~ 2.Qe3, but 1…Kxd3! refutes, and 1.Qc1? 1…Sg~ 2.Qg1, but 1…Sf2! refutes.

Andy Sag: Note the thirteen pieces. Can it be reduced to twelve? Tried removing the g3-pawn but then 1.Qg3 is a cook. However, you can actually remove that pawn if the queen starts from d2; then the key 1.Qf4! is sound and you still get three changed mates.

The key 1.Sc4! shuts off the black queen to threaten 2.e4. A wealth of strategically interesting play follows, with the black knights having a starring role in five of the eight variations. First the pair allow the R + B battery to operate by interfering with the f7-pawn: 1…Sgf6 2.Bxd7 and 1…Sdf6 2.Bxg4. Next they unguard a mating square and cut off the g1-bishop: 1…Sf2 2.Se3 and 1…Sc5 2.Sxb6. Lastly the g4-knight closes the same bishop line with 1…Se3 2.Qxd3. Another interference on e3 occurs in 1…Be3 2.Qh1, when the unpinned rook cannot interpose on the long diagonal. The self-block 1…Re6 enables White to utilise the battery once more: 2.Be4. Only one variation, 1…Qxc4 2.bxc4, lacks any line effects.

Dennis Hale: My favourite variation is 1…Be3 2.Qh1. Nice to see a problem from the great English composer.

There is significant set play consisting of 1…Rxd5 2.Qxd5, 1…Sxf5 2.Rxf5, and 1…a2 Qb2. The white queen takes a backward step with 1.Qe1! to subtly threaten a corner mate (2.Qa1), and also grants a flight on d4. The three set variations are abandoned by the key, but two of these set defences result in unexpected new mates given by the Q + P battery: 1…Rxd5 2.exd5 and 1…Sxf5 2.exf5. A third battery mate delivered by the e-pawn follows if Black takes the flight: 1…Kd4 2.e5. Additional variations are 1…b3 2.Qc3, 1…Rxc4 2.Bf6, and 1…Se6 2.Sxc6.

Composer: Two tries are 1.Qd1? (2.Qa1) b3! and 1.dxc6? (2.Qd6 and 2.Rxa5) Sb7! The latter is aggressive but the point of interest is that by occupying c6 the white pawn prevents 2.Sxc6, leaving the d8-knight free to move to b7 which neatly defends both threats. The d8-knight also prevents 1.Rxc6 from being a cook by defusing 2.Re6, thus leaving the h6-knight free to move to stop 2.Bf6.
Paz Einat: Excellent key with two mate changes and central role for the pawn battery.
Jacob Hoover: Nice one, Andy. It's always a pleasure (at least for me!) to see the battery play in action.

It’s a pity that this fine two-mover is largely anticipated by the problem below, as reported by Geoff Foster. He writes, “This is very similar to Andy's, with the extra nice feature of the thematic black defences being checks, making the set play more noticeable.”

See text above.

Set play: 1…Bxe5+ 2.Qxe5 and 1…Rc5+ 2.Rxc5. Key: 1.Qd1! (2.Qh1). 1…Bxe5+ 2.dxe5, 1…Rc5+ 2.dxc5, 1…Ke4 2.d5, and 1…g3 2.Qf3.

The solutions are 1.Sfxd5+ Qg7 2.Sf6 Qg1, 1.Sbxd5+ Qc5 2.Sb6 Qf5, and 1.Bxd5+ Qb4 2.Bc4 Qe1. White does not have time to move the d-pawn to let the a8-bishop control the flights on f3 and g2, because the white queen will require two moves to set up a mate. So Black aims to open the long diagonal for White by removing the d-pawn. Each possible capture of the d-pawn is also a discovered check, however, and this determines the white queen’s first move which must answer the check by interposition. The queen move is thus a self-pin. And when the black piece on d5 moves to open the long diagonal, it performs a switchback so as to unpin the queen, which is freed to give a different mate each time. Three closely matched solutions showing good strategic effects.

The a6-bishop’s half-pin of two black pieces produces the set variation, 1…R~ 2.Se3. A good withdrawal key 1.Bc8! gives up the half-pin and threatens 2.Bxh3. Now 1…Rf5/Rh5 is answered by the changed mate 2.Qa1. A second corner-to-corner queen mate occurs with 1…Sf5 2.Qh1. After 1…B~, the queen delivers yet another long-range mate, 2.Qg2. There’s one line of by-play: 1…Se3 2.Sxe3.

Composer: Meredith (twelve-piece) setting with threat and four variations, one changed mate, and two tries, 1.Qf3? (2.Qd1) Re5! and 1.Bxb5? (2.Qa1/Se3) Se2! The latter defence unpins the c4-knight so neatly defends against both threats; also this move of the g3-knight still maintains a defence against 2.Qh1 as it can then interpose on g1.
Jacob Hoover: The queen is pretty much the star of the show, delivering almost every mate in the actual play. As far as I'm concerned this counts as a theme, which I have taken to calling “Girl Power.” Another great one, Andy. The half-pin red herring made it memorable.

Set mates are prepared for all possible black moves in the diagram. The waiting key 1.Kd2! largely preserves the set play while adding two more variations. Two black defences open lines for the white queen: 1…R~ 2.Qe5 and 1…Bg8 2.Qh1. The e7-pawn commits three self-blocks: 1…e5 2.Sgf6, 1…e6 2.Bc6, and 1…exd6 2.Sef6 (the set dual 2.Sef6/Sc7 has been removed). The added play consists of the flight-taking 1…Ke4 2.Bc6 and a nice en passant avoidance, 1…d3 2.e4.

Jacob Hoover: A random king move grants a flight on e4 that is answered with 2.Bc6, but 1.Kc2? fails to 1…d3+! Only 1.Kd2! works, answering 1…d3 with the pin-mate 2.e4.

The key 1.Sf7! covers d6 so as to threaten 2.Sd7, which interferes with the white queen’s control of the d-file. The d4-knight and e3-queen are half-pinned by the white bishop, and when either moves off the diagonal to answer the threat, White could exploit the pin of the remaining black piece. Any move by the knight on d4 defends by vacating that square for the king, and leads to two potential mates by the g2-rook; but in every case the knight move has an arrival effect that forces a single mate: 1…Se2/Sb5 2.Rg5 and 1…Sxb3/Sc6/Sxe6/Sf5/Sf3 2.Rxc2. The black queen has two capture defences aimed at creating more flights: 1…Qxe4 2.Qa5 and 1…Qxb3 2.Qc7. Four different pin-mates are hence realised in these thematic variations.

Jacob Hoover: 1…Qxe4 2.Qa5 shows a change from the set play, 1…Qxe4 2.Sxe4. A quite lovely demonstration of the half-pin theme, with no by-play at all.

This miniature is solved by a withdrawal key 1.Ba6!, which grants a flight on g2 and entails two threats: 2.Bb7+ Bg2 3.Rd1 and 2.Rd1+ Bf1/Kg2 3.Bb7. These threats are separated or individually forced by 1…Bf1 2.Bb7+ Bg2 3.Rd1 and 1…Bg2 2.Rd1+ Bf1 3.Bb7. The remaining defences are all answered by the same bishop check, though a variety of mates follows. 1…Kg2 2.Bb7+ Kf1 3.Rd1, 1…Bxd7 2.Bb7+ Bc6 3.Bxc6, 1…Be6 2.Bb7+ Bd5 3.Bxd5, 1…Bf5 2.Bb7+ Be4 3.Bxe4, and 1…Bg4 2.Bb7+ Bf3 3.Bxf3. Not 1.Be2? (2.Bf3+/Rd1+) Bg4! or 1.Bb5? (2.Bc6+/Rd1+) Bxd7!

Jacob Hoover: This problem was way too easy… or I've gotten a lot better at three-movers by now. Either way, this miniature was a nice one.
Nigel Nettheim: Easy to solve, but nice. It seems surprising that this could be done with no short mates or duals (apart from the dual threats).

The thematic try 1.Sg6? threatens 2.Se7 but also cuts off the h7-bishop’s control of e4. 1…Bh4 is answered by 2.Sgf4 (re-opening the bishop-line) and not 2.Sdf4? which would create a flight on e4 by closing the g4-rook’s line. 1…Ra7 permits another knight mate, 2.Sb4. But 1…Qh4! defeats the try because 2.Be4 is disabled. The key 1.Sc6!, with the same threat as the try, interferes with the c8-rook’s control of c5. Now 1…Bh4 provokes a new mate, 2.Sf4. After 1…Ra7, White must choose 2.Scb4 – another changed mate – and not 2.Sdb4? which would allow the king to escape to c5 by closing the a3-bishop’s line. The changes between the try and post-key phases are brought about with sophisticated and closely matching line strategy. The by-play consists of 1…Qh4 2.Be4 and 1…e5 2.Bg8.