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401. Ottavio Stocchi
The Brisbane Courier 1933
11th Hon. Mention
Mate in 2

Four set variations account for all possible black moves in the diagram: 1…Kc6 2.Qb7, 1…Se~ 2.Qe4, 1…c6 2.Qd4, and 1…Sg~ 2.Bf3, so this is a complete block. White has no way of preserving all of these lines though, e.g. 1.Bd1? Se2!, 1.Be3? c5! The key 1.Qb5! (waiting) removes the flight on c6 but creates a new one on e4: 1…Ke4 2.Qc4. The e7-knight now exhibits correction play, 1…Se~ 2.Re5 and 1…Sc6 2.Bb4, bringing about two changed mates. A third change occurs with 1…c6 2.Qd3, while 1…Sg~ 2.Bf3 is as set. An especially difficult mutate with some surprising changes.

Andy Sag: The give-and-take key changes three mates as well as the flight. Noted the white pawn on a5 prevents the 1.Sa5 (2.Qc4) cook.
Jacob Hoover: The c5-bishop has numerous tries (1.Bf2/Be3/Bxa7?), all of which produce the changed mates 1…Se~ 2.Qc5 and 1…Kc6 2 Qc5, but they're all defeated by 1…c5!
Nigel Nettheim: The refutation of the try 1.Bd1? is neat. After 1.Qb5! Ke4 the pin of the e7-knight is irrelevant, perhaps a slight weakness.
Ian Shanahan: A beautiful mutate with a key that gives and takes a flight. Lovely (though the position is rather crowded, as is so often the case with Stocchi).

402. Brian Tomson
feenschach 1983
Series-helpmate in 29

If the two f-pawns were removed in the diagram position, the f8-rook could mate, and indeed it’s not possible to arrange any other mating configurations, given the fixed positions of the white units. Black must capture the f6-pawn with the king, since to do so with the rook would give check (forbidden during the sequence). This plan requires the black king to be shielded from all three white line-pieces: 1.Rg2 2.Kg1 3.Kf1 4.Re2 5.Re3 6.Ke2 7.Kd3 8.Kd4 9.Re7 10.Rf7 11.Kd5 12.Ke6 13.Kxf6. Now if Black captures the f4-pawn too soon, the opened f-file would mean the king cannot return to h1, as the black rook is unable to shield the king from both white rooks simultaneously. So the king goes back first: 14.Ke6 15.Kd5 16.Kd4 17.Re7 18.Re3 19.Kd3 20.Ke2 21.Kf1 22.Re2 23.Rg2 24.Kg1 25.Kh1. Finally the f4-pawn can be captured, followed by the rook’s return to h2: 26.Rf2 27.Rxf4 28.Rf2 29.Rh2 for 29…Rf1. An impressive black minimal problem that features numerous shields and rundlaufs by both black pieces.

Andy Sag: The mate is not hard to see, but how to get rid of the f-pawns in as few moves as possible avoiding checks leads to a unique series.
George Meldrum: A tortuous path but one without compromise on move order or move direction.
Ian Shanahan: A beautiful and perfectly constructed example of well-known ideas: king-shields, encirclement, a long trek with subtle manoeuvring and precise switchbacks.

403. David Shire
Australian Chess 2003
Mate in 2

After the key 1.d6!, Black can stop the threat of 2.Qxe5 by capturing the knight on d3. Such a capture would self-block and apparently enable the white rook to give various battery mates by moving along the f-file. But each capture by a black piece involves an additional effect that obliges the rook to play to one specific square: 1…Bxd3 2.Rf1, 1…Sxd3 2.Rf2, 1…cxd3+ 2.Rf7, and 1…Rxd3 2.Rf4. The multiple self-blocks on the same square lead to differentiated white mates or dual avoidance – a combination known as the Stocchi theme. There is by-play with 1…Rd5 2.Qe3.

Andy Sag: The key allows a check. This and three other set self-blocks after capture of the d3-knight require four different positions of the white rook when firing the battery. Note the rook capture requires a double check. Finally, the rook blocks the threat but again opens the line to e3 as well as creating a self-block on d5.
Jacob Hoover: If we were to replace the d3-knight with a dummy black piece, White would have five different mates: 2.Rf8, Rf7[A], Rf6, Rf2[B], Rf1[C]. Three of the four captures of the knight force a particular one of these rook discoveries: [A], [B] and [C]; thus, we have an incomplete Stocchi block since there is no capture that forces 2.Rf8 or 2.Rf6. The fourth capture, however, forces a new rook discovery: 1…Rxd3 2.Rf4.
Nigel Nettheim: Not hard to solve, because the a2-g8 diagonal was likely to come into play. But the four captures on d3 are very nicely handled.
George Meldrum: A quiet unassuming key move. Four defensive captures on d3, all with unique mating responses. Very nice.
Ian Shanahan: Four-fold Stocchi blocks – self-block plus dual avoidance – on d3. From memory, the record is five. An excellent problem!