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476. Molham Hassan &
Geoff Foster
Australasian Chess 2010
Mate in 2

A good key 1.Qh4! grants a flight on e5 and sets up a battery on the fourth rank, which threatens to open with 2.Sg6. The black knight has three defences that allow the h8-bishop to cover the e5-flight, and they produce three more battery mates: 1…Sh5 2.Sxh5, 1…Se6 2.Sxe6, and 1…Sxf5 2.Sd5 – the latter a pin-mate where White regains control of e3 and d4. A switchback occurs if Black takes the offered flight: 1…Kxe5 2.Qe7. Lastly, 1…d2 is answered by 2.Re2. The three battery variations show a duel between the two knights.

Andy Sag: A flight-giving key with switchback. I like the two variations that self-pin the black knight.
Jacob Hoover: The black knight has three defenses, and each one forces a different knight discovery.
Ian Shanahan: The two star variations are 1…Kxe5 2.Qe7 (the black king takes the flight proffered by the key, met by a switchback and pin-mate), and 1…Sxf5 2.Sd5 (the Schiffmann theme). A fine problem in traditional style.

477. Alfred Figdor
The Australasian Chess Review 1943
1st Prize
Mate in 3

The white knight on f2 has four moves that threaten mate, but three are defeated by its capture while 1.Sg4? is neutralised by 1…Rxb6! The key 1.Ba4!, threatening 2.Be8 and 3.Bxf7, induces Black to disable the four potential defences against the knight moves. 1…c6/Rxa4 2.Sg4 and 3.Sxf6. 1…Bb1 2.Sh1 and 3.Sxg3. 1…c3 2.Sd3 and 3.Sf4. 1…d4 2.Se4 and 3.Sxf6/Sxg3. Consistent white knight play and in three variations Black deftly handles the threat by activating the a2-bishop.

Jacob Hoover: White unravels this problem with 1.Ba4!, sacrificing the bishop to the a6-rook. In each line a black unit either is decoyed away from guarding a vital square or blocks a guard of a vital square.
Andy Sag: The four set plays by the f2-knight make a nice theme.

478. Efren Petite
Australian Chess Problem Magazine 1997
Mate in 2

A white bishop move along the long diagonal will open the e-file and threaten 2.Qe4, a mate that requires the queen to observe both e6 and c4. Black can defend by placing a knight on e5 or d4, moves that also pin a white rook and thereby prevent it from mating on an unguarded square. In two thematic tries the bishop is placed to interfere with one of these pin-lines: 1.Bg7? Se5 2.Rxd6 (1…Qxe3 2.Sxe3, 1…Sd2 2.Sc3) but 1…Sd4! refutes, and 1.Bb2? Sd4 2.Rxc5 (1…Qxe3 2.Sxe3, 1…Sd2 2.Sc3/Rxc5) but 1…Se5! refutes. The key 1.Ka6! creates a new threat of 2.a8(Q), against which the knight defences also work. But thanks to the anticipatory unpinning effect of the king move, these defences no longer counter the rook mates: 1…Sxe5 2.Rxd6 and 1…Sd4 2.Rxc5. The key-move controls b5 so that if Black takes the flight, the threat is still playable: 1…Kc6 2.a8(Q); hence not 1.Kc8? Kc6! Another good try is 1.Re7? (2.Qe4) Sd4 2.Qxd4 (changed mate), 1…Bxe7 2.Sb6, but 1…Qxe3!

Andy Sag: The key breaks two half-pins. It also gives a flight which is illusory as it fails to defend the threat. The bishop tries involve the same defences which use rook pins to work.
Andrew Buchanan: Found this very hard to solve, because of so many tries. I was particularly enraptured by 1.Bb2? and 1.Bg7?
George Meldrum: The tries 1.Bb2 and 1.Bg7 look tempting yet fail. Next attention is drawn to the innocuous pawn on a7 but immediate promotion fails. The flight-giving key looks an unlikely move. So many good problems have an obvious key – this is not one of them.
Ian Shanahan: The rook-mates thwarted in the tries occur as mates after their black refutations in the post-key play! A classic reversal-pattern. A heavy, but satisfying problem.

479. H. Cox
The Australian Problemist 1963
Mate in 2

White mating replies are prepared against all possible black moves in the diagram: 1…Sc~ 2.Re6, 1…Se~ 2.Sdc6 (dual 1…Sd5 2.Sdc6/Sbc6), and 1…e3 2.Sf3. But White has no waiting move capable of preserving all of the set play, e.g. 1.Kxg3? Sxf5+!, 1.Qg5? h4! The unexpected key 1.Sb5! (waiting) abandons not only both set knight mates but also the rook mate on e6 (by unguarding f5). Three new mates arise, however, due to a multitude of effects brought about by the key: 1…Sc~ 2.Rxe4, 1…Se~ 2.Rxc5, 1…Sd5 (correction move) 2.Sc6, and 1…e3 2.Qd4. The key-piece has to choose b5 to place an extra guard on d6, otherwise 1…Se6! would be too strong. The composer Cox had a knack for creating mutates that are difficult to solve.

Andy Sag: A waiter with four variations including three changed mates. Can convert to a Meredith by shifting the white king to e1, removing the g-pawn and moving everything else down one square.
Jacob Hoover: A rather nice block-mutate.
George Meldrum: Heaps of changed mates; dual eliminated. Nice.
Ian Shanahan: A lovely all-change mutate with a black correction in the post-key play. Very pretty and elegant!

480. Ian Shanahan
Springaren 2012
Helpmate in 5½

The attractive diagram position exemplifies one-row asymmetry, where a symmetrical set-up nevertheless yields a single solution, by utilising the board edge in some way. 1…Kf5 2.Sf3 g4 3.Se5 g5 4.Sf7 g6 5.Kh6 g7 6.Sh8 gxh8(Q). Good black and white interplay ensures that the knight route to h8 is unique, and there’s an ideal-mate finish.

Andy Sag: A pawn mate is possible using the knight as a self-block but that takes seven white moves, so promotion to a queen on h8 is clearly indicated. The black king must wait for the pawn to arrive at g6 before moving and the knight must go via e5 to keep the g-file clear thus ensuring unique play.
Andrew Buchanan: Crafted with Ian’s usual elegance and attention to detail. A pleasure to see why the black knight could not land on any other square on the h-file.

481. Alex Boudantzev
Friends of Chess 1972
3rd Prize
Mate in 2

The B + R/R half-battery on the long diagonal and the Q + S battery on the first rank are both controlled by the black queen. If either rook moves off the diagonal, White will threaten Rf4 by the other rook, shutting off the queen. Random moves of the two rooks are mostly defeated by 1…Bf5!, which not only stops Rff4 directly but also cuts off the g6-bishop to create a flight on b1. The thematic try 1.Rb6? forestalls 1…Bf5 by guarding b1 and it leads to 1…Qd6+ 2.Rdxd6, 1…Qh3 2.Rd3, and 1…Qxg2 2.Rd2 (plus various Q + S battery variations similar to the post-key play), but 1…Qg1! refutes. The key 1.Rd7! (threat: 2.Rff4) prevents the bishop defence and produces 1…Qd6+ 2.Rfxd6, 1…Qh3 2.Rf3, 1…Qxg2 2.Rf2 (three changed mates compared with the virtual play) and 1…Qg1 2.Rf2. Further, 1…Qg3 2.Sf2, 1…Qe5 2.Se3, 1…Qc7 2.Sdc3, and 1…Qb8 2.Sdb2 show more precise battery shut-offs. Including the virtual play, we see ten distinct battery variations (counting 1…Qxg2/Qg1 2.Rf2 as one), all instigated by the black queen.

Andy Sag: The diagonal half-battery gives a strong clue and the first rook must block the c8-h3 diagonal but the correct rook must be chosen because 1.Re6? fails to 1…Qg1/Qh3! All eight mates are battery mates including the threat.
Andrew Buchanan: Black is threatening 1…Qd6+ [an unprovided check], and that forces the key to be by one rook.
George Meldrum: But which rook move? That that stops Black playing 1…Bf5 and provides a mate after Black playing 1…Qg1. Eight mates in a cornered king problem; what’s not to like!
Jacob Hoover: This is an absolute gem of a problem.
Ian Shanahan: Classic half-battery involving numerous tries, with the black queen losing focal control of each of the two battery lines in turn thence being shut off by one of the batteries’ firing pieces for her troubles (the Mackenzie theme). A ‘trying’ problem, difficult to solve, but flaunting rich play and numerous changes between try and key.