Anton Baumann: Mattdual in b): 3.Tb8 axb8=D,T# (2022-12-16)
A.Buchanan: So Borodatow got it all working! In a) Black might have captured hxgxf and axPb. So castling rights might still be maintained with the ep. In b) on the other hand, it must be axb, bxa, exf and wPgxh6, so there was the cage. Promotion to TD is tolerated in the final move, although it may not be puristic, without the convention, too many mates would be excluded (2022-12-16)
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Anton Baumann: Neufassung vergl. P0006288 (2023-01-06)
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See P0000674
Henrik Juel: The stipulation should probably read h#2.5: 1.exf6ep 0-0-0 2.Bxf4 Rd7 3.a8Q# (2003-08-18)
Anton Baumann: Letzter Zug war f7-f5, sonst retropatt. Die weissen Bauern haben 6x geschlagen. Der s a-Bauer wurde so ebenfalls als Schlagopfer benötigt und musste 2x schlagen, um sich umwandeln zu können. Weiss hat also auf h6 den s Bauern geschlagen. Unabhängig davon ob der sTe6 ein Umwandlungsturm ist oder nicht, muss der sTh8 über e8 aus der Ecke gekommen sein. Also ist die Rochade illegal!
Autorabsicht: 1. ... exf6 e.p. 2.0-0-0 Lxf4 3.Td7 a8=D# ist die Verführung!
Lösung: 1. ... Kxf4 2.Tf6 e6 3.Tf8 Sg7#
leider geht auch: 1. ... Kxf4 2.Te7 e6 3.Tb8 axb8=D,T# (2022-12-13)
A.Buchanan: I agree Anton. I suggest as a fix -bBa6 +bDc2. I think retro, solution and try all work correctly now. Do you folks agree? (2022-12-13)
Anton Baumann: Der Vorschlag von Andrew ergibt eine korrekte Lösung, aber nicht im Sinne des Autors: ohne einen s Stein auf a6 ist f6-f5+ als letzter Zug möglich, d.h. kein Retropatt weil Weiss a6-a7 zurücknehmen kann! 1. ... exf6 e.p. ist deshalb nicht zulässig. LB wollte aber dass f7-f5 der letzte Zug war, damit aber die Rochade illegal ist! (2022-12-14)
Anton Baumann: Mögliche Korrektur: a6=sL, g2=sD (2022-12-15)
A.Buchanan: Yes I agree. I had overlooked the unmove of wPa7 (2022-12-15)
A.Buchanan: The new form is now quite nice, and should be posted here in PDB. Alas I can't take much of the credit, all I spotted was that bPa doesn't have to be on the board: the number of black PCs is the same. (2022-12-15, hidden) more ...
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Moldenhauer: Ergänzung Stelvio 1.2 C+: Keine Lösung: BP 8.5, 9.0.
10. dxc6ep++ Doppelschach. (2023-05-24, hidden) more ...
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Branko Koludrovic: P.S.
The black pawn a4(on the diagramm)came from c7 after capturing the white bishop on b6, then moving to b5 and capturing a white officer on a4. (2010-09-28)
A.Buchanan: I think sBf must have captured on g2 & then promoted on f1 to S, otherwise it’s impossible to unlock the southeast cage (2023-07-11)
A.Buchanan: So that means it’s sound. However I don’t see that it needs to have been sL shielding on f1 (2023-07-11)
A.Buchanan: Can sBf capture to e-file to be captured directly by wBf rather than capture to g2 to promote? If so, then sBf could capture L on a dark square, meaning that last move could have been c6xb5 (2023-07-11, hidden) more ...
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Henrik Juel: 0... fxe3ep 1.d8S Kxd5 2.0-0-0#. Not -1.f2? and Lg1 is caught. (2004-09-16)
Vaclav Kotesovec: Similar problems should not be labeled as "C+". Such a designation is only acceptable if the entire analysis was performed by a computer program. (2023-08-03)
Henrik Juel: In principle I agree, Vaclav
But PDB does not (yet) allow HC+, so I find it acceptable to use the C+ label, when you also tell the whole story after 'Computer test:' below (2023-08-03)
A.Buchanan: Hopefully Gerd will have more time at some point, and can expand the functionality in this and other areas. In the meantime, engine solving of conventional retros including AP, is in its infancy. Retractor 2 has some effectiveness, but is still basic. And there is nothing that yet grasps the intricacies of castling/ep etc. However AP problems do often contain considerable forward chess, and the C+ tag is very useful to filter out those that have already been solved forwardly, without pretending that these are in any sense fully solved (2023-08-04)
Ladislav Packa: I know the definition of AP, but I don't understand the logic behind it. The move 1.fxe3 e.p. proves that White CAN castling. But the solution (2. ...Rd1#?) claims that castling is MANDATORY. From my point of view, AP is correct when only castling is necessary for the solution and the Rook move would be a dual. (2023-08-04)
A.Buchanan: @Ladislav: I am not sure how to help you. Maybe you can read this page from Retro Corner: https://www.janko.at/Retros/Glossary/APosteriori.htm (2023-08-05)
Ladislav Packa: Andrew, what should the article help me with? I quote the final sentence:
Some people still oppose this rule and argue that it should certainly not be the default convention. (2023-08-05)
Henrik Juel: You could view it this way, Ladislav
h#2 means that it is Black to move, so White made last move
What was last move? A little analysis shows just three possibilities: f2-f4, move by Ta1, or move by Ke1
So normally we cannot assume that last move was f2-f4
But if White can castle, then the last move was f2-f4
So if we could start with 0... 0-0-0, then 1.fxe3ep would be legitimate
AP says that you are allowed to reverse the sequence of events; first do the ep capture, then later legitimize it by castling
Was this helpful? (2023-08-05)
Ladislav Packa: Henrik, you don't have to explain that to me. I've done a few AP issues myself, like P1348357. But that doesn't mean I agree with AP's logic. I already wrote it - the term "you can castle" is applied as "you must castle". But these are only problems where, in addition to castling, the Rook move can also be used, I consider that a dual.
From that point of view, the P1000662 issue is perfectly fine for me. (2023-08-05)
Joost de Heer: AP: By castling, you prove a posteriori that the ep-capture was not just a try but the actual solution. Without castling, the ep-solution just is that: a try.
So: Try 1. fe3 ep e8=S 2. Kd5 Rd1 - but ep capture not allowed, as there is no proof that f2-f4 must've been the last move.
Solution 1. fe3 ep e8=S 2. Kd5 OOO - Now the ep capture was justified because white castled, thereby proving that the last move before the diagram position indeed was f2-f4. (2023-08-06)
Joost de Heer: See e.g. P1052919 : The try is an ep capture which is unjustified. (2023-08-06)
A.Buchanan: OK Ladislav: I think I get your point. If one solution with castling justifies the e.p., then based on that certainty, why shouldn't an alternative solution with no castling *then* be allowed as well? There are problems in which one twin shows 0-0-0 and the other shows 0-0. Each is based on the other in a similar way, so the idea of dependency is not new. Why are we not allowed to add other "parasitic" solutions as well? Why can we only have the "paying" solutions? We can't say that we are restricted to one solution: that's not the way chess problems operate! And this is just in the help world - in the adversarial world it might get even more complicated. Is this your issue, Ladislav? (2023-08-07)
Ladislav Packa: I don't want to unnecessarily prolong this discussion. However, I will add one more note: in this position, white castling is also possible without e.p. in Black's 1st move. If B1 were an indifferent move, then white can 1...0-0-0! The Codex of Chess Composition writes about it in Article 16 (1):
Castling convention. Casting is permitted unless it can be proven that it is not permissible.
In our case, 0-0-0 is possible because White's last move exists - e2-e4! It does not matter if it is this move or some a2-a3, both moves are equivalent. EP does not prove the possibility of casting, it would be legal even without it. (2023-08-07)
A.Buchanan: Ladislav was what I wrote your issue pls? Y/N :-) (2023-08-07)
Ladislav Packa: I have no problem, I'm just expressing my own opinion about the AP convention. (2023-08-07)
A.Buchanan: OK cos I think the point I raised is a real one that should be addressed by theory some day. Clearly from the nice problem that you composed Ladislav you understand the mechanics very well. From a justification perspective it's all a bit iffy, but that's why it's controversial. Under RS it's really the only way one can end up actually eping, and it's proved compositionally fertile. So that's enough to justify (2023-08-08)
Ladislav Packa: No need to apologize. This is a normal discussion with different views on the issue. Maybe it will come to some conclusion.
I just want to point out the fact that it is not the e.p. that authorizes castling, because according to the Codex castling is possible regardless of the e.p. It's the exact opposite: castling authorizes the possibility of e.p. (2023-08-08)
Joost de Heer: "I just want to point out the fact that it is not the e.p. that authorizes castling, because according to the Codex castling is possible regardless of the e.p. It's the exact opposite: castling authorizes the possibility of e.p."
You misinterpret AP. The e.p. capture does not authorize castling, castling provides a justification later on (hence the 'a posteriori') for the legality of ep.
Usually, for ep justification you need to examine all game trees that lead to the diagram, and only if all game trees end with the double-step, then ep is allowed.
With AP, you examine all the game trees including the actual play. If all those game trees have as last move before the diagram position the double step, then ep is possible.
In this case, if white doesn't castle, then there are game trees which don't have as last move the double step, and therefore AP logic dictates that the ep capture was illegal. However, all game trees which lead to the diagram and which have castling in the actual play have as last move before the diagram position the double step, hence AP dictates that the ep capture is legal. (2023-08-09)
Ladislav Packa: Joost: A simple question - is white allowed to castle after any 1st move by black (except e.p.)? (2023-08-09)
Joost de Heer: Of course he is. AP only is used to combine the ep justification with castling, not the castling right per se. (2023-08-09)
A.Buchanan: I agree with both. Also "cooked" is closer to "unsound". And we choose not to have "C+ cooked", which might legitimately mean "C-" (2023-08-04, hidden) more ...
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Kommentare:
Als einziger letzter schwarzer Zug, der die weiße Rochade
erhält, kommt nur Bh7-h5 infrage, was dem Weißen den e.p.-Schlag
ermöglicht, um nicht die Rochade oder das Mattnetz zerstören zu
müssen (H.P.Suwe)
Gianni Donati: This intends to show the Valladao theme in the minimum number of moves. (2004-03-19)
VL: The waiting ep capture. Cf. also P1000260
(by T.Petrovic, 2000) somewhat enriched
thematically with the illegal try 2... Rd1#??. (2004-06-03)
A.Buchanan: The “illegal try” 2. Rd1+ is not actually mate because c2 is unprotected. This is kind of “logic dual” spoils the A.P. motivation for the castling (2020-05-20)
Henrik Juel: White captured h6xg7 and once more, e.g. axPb-b8=Y
Black captured cxdxe, dxexf, fxg, and once more, e.g. a2xb1=Y
Possible retroplay 1... h7-h5 2.h6xSg7 Df8-f4 3.h5-h6 Sf4-h3 4.Sh3-g1 etc., preserving the castling right
Any other black last move would force White to retract Ta1, as d2xc3, d2xe3, and h6xh7 would be illegal retractions
I agree with Andrew that the double motivation of 2... 000# is a weakness:
a. legitimizing h7-h5
b. mating (2020-05-21)
Vaclav Kotesovec: Similar problems should not be labeled as "C+". Such a designation is only acceptable if the entire analysis was performed by a computer program. (2023-08-03)
A.Buchanan: See discussion at P0009121 (2023-08-04)
A.Buchanan: Maybe can replace wPf2 with wR, wRf1 with wB & shift bPg3 to g2? (2020-05-20, hidden) more ...
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No. 11661 HN
A.Buchanan: “Obvious promotion” is intended to refer to something visible in the initial diagram position, not what is reached during series play (2022-09-14)
A.Buchanan: Similarly “non-standard material (2022-09-14)
paul: La solution commence avec 1.d4xc3 e.p.! La source est diagrammes 148/2004. (2011-07-03, hidden)
A.Buchanan: Similarly “non-standard material”, though this is not present in the problem at any point. (2022-09-14, hidden) more ...
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Michel Caillaud: cooked by Dmitry Baibikov :
3.Sb7xLa5(+wBa3) Kb4xPb5(+sLa5)+ -4.Ta5xLa4(+wSd3)+ e5xSd4 (2022-07-19)
Kevin Begley: correction: P1404688 (2022-09-27)
KB: -1.O-O [+wPc4]+ ...bPd4x(wQc3,wPc4) e.p.!!
-2.c2-c4 [+wQc3]+ ...bPb2xwQc1=S [+bBb4]+
-3.wSb7xbBa5 [+wPc2] ...bPe5xwPd4 [+bBa5]+
-4.wPa5xbBb6

Valladao hidden in complex retro-play. (2007-10-02, hidden) more ...
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Henrik Juel: Stelvio 1.31 found the solution immediately and tested it unique in 9 minutes (for the first 25.0 moves) (2023-06-13)
Henrik Juel: C+ by Natch 3.1 (38 m, utilizing the final ep)
No solution in 24 or 25 (2018-12-23, hidden) more ...
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Henrik Juel: C+ Popeye 4.61 and analysis (2022-09-11)
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A.Buchanan: The retro content here is fun, but I don't see why it's suggested that this is AP. (a) is a cant castler, and (b) is a standard PRA matrix. Removing AP as a keyword for this one. (2023-07-21)
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En passant als Tempozug. Die Grundidee (Einfachschritt des wB ist im Gitterbrett automatisch ausgeschlossen) kann man schon in Fairy Chess Review finden. Hier ist sie mit Rochade garniert in offener Stellung. die jedoch keinen anderen letzten Zug erlaubt. (Autor).
Ganz toll gemacht! (HB).
Raffinierter Zugzwang (KF).
Das ist schon gemein, was der Autor mit den Lösern vorhat (HM).
Viel Gitterschach (Doppelschritt, Retropatt des Tg7 und Rochade trotz Le2) läßt den bekannten e.p.-Trick in neuem Licht erscheinen (MR).
Henrik Juel: Where is the promotion needed for Valladao? (2024-02-04)
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Henrik Juel: Popeye 4.61 with 'opt enp b3' found no solution (2022-05-27)
Gerald Ettl: Schaut so aus, als ob die sDa5 nach e5 muss. 1.axb3 ep Sa5+ 2.Kxd5 0-0-0# (2022-05-27)
Gerald Ettl: aber auch 2.-Td1# ? (2022-05-27)
Henrik Juel: Andrew, can you throw any light on this problem? (2022-05-28)
Henrik Juel: Gerald, in AP problems like this one White must castle to legitimize the ep capture key (2022-05-28)
A.Buchanan: Hi Henrik, Gerald. I found this one in WinChloe with the current diagram. It gave the "solution" 1. axb3ep+ Sxa5+ 2. Kd5?? 0-0-0#. However when I tried running the WinChloe solver just now, it said there's no solution. Quite right: Rf5 controls d5. I don't think we can shift Qa5 to e5 though.
My first thought is that wPd5 should be on e5. Check my suggested solution in the solution text. However, as you will see, I think we need a second thought as well! Hope the finest retro minds can figure this out. Failing that, we could ask Igor. (2022-05-28)
Mario Richter: The diagram in the reprint in 'Uralsky Problemist' is exactly as given here. The solution given there without further explanation is: 1. ab+ (e.p.) Sxa5+ 2. Kd5 0-0-0#!
Notice that the second black move doesn't contain a capture sign!

Some typos in Andrew's analysis:
The black potential promotion squares should be c1 and g1.
White's last move couldn't have been b3-b4?? simply because that would give an illegal check. (2022-05-28)
A.Buchanan: Thanks Mario for the careful reading. I’ve fixed the errors. Pd5 may be a typo in the reprint then. It also creates a bogus retraction d4-d5, so I don’t think it can be right. Now for Igor. (2022-05-29)
A.Buchanan: Joaquim Crusats spotted R: 1. b2-b4 Kb4-c4+ 2. Sd6-b7, which I'm sure is the intended retraction. So we diagnose a single typo that occurred in the Uralsky reprint diagram: wPe5 appeared on d5. I suggest correcting it here. (2022-05-30)
A.Buchanan: Author confirmed this was a typo (2022-11-23)
A.Buchanan: It was reprinted as 18 p5, Uralsky Problemist 13 (Feb 1998), if anyone here has access to that. (2022-05-28, hidden)
A.Buchanan: R: 1. b2-b4 Kb2-c4+ 2. Sd6-b7 (2022-05-29, hidden)
A.Buchanan: R: 1. b2-b4 Kb4-c4+ 2. Sd6-b7 (2022-05-29, hidden) more ...
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Posthum innerhalb eines Nachrufes auf Marco Bonavoglia veröffentlicht.

Antonio Garofalo: "Marco, mentre era in ospedale, mi ha inviato questi due problemi, uno augurale, l'altro per la competizione fairies. Sfortunatamente egli non può vedere i suoi lavori pubblicati, essendo deceduto nelle prime ore del 5 dicembre 2022..." [Marco schickte mir, während er im Krankenhaus war, diese beiden Probleme [dieses und P1406940], eines für seine [Neujahrs-]Wünsche (P1406940), das andere für den Wettbewerb, Abteilung Märchenschach. Leider kann er seine veröffentlichten Werke nicht mehr sehen, denn er verstarb in den frühen Morgenstunden des 5. Dezember 2022.]
Joost de Heer: C+ Popeye with 'opt enp e2e3e4'.
Too bad there isn't a try without castling. (2023-04-04)
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Objective: co-record shortest achievement of task, followed by artistic continuation.
Also version rnbqBbnr/pp2p1Bp/3P1pp1/4N2k/4P3/1Q5P/PP3P1P/RN1R2K1 PG in 14.0 mentioned in article. This offers different artistic continuation (with Pronkin instead of Ceriani-Frolkin).
Henrik Juel: C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: 1.Pe2-e4 Pc7-c5 2.Bf1-b5 Pc5-c4 3.Sg1-f3 Pc4-c3 4.O-O Pc3xd2
5.Pc2-c4 Pf7-f6 6.Qd1-b3 Pd2-d1=B 7.Bc1-h6 Ke8-f7 8.Pc4-c5+ Pd7-d5
9.Pc5xd6ep+ Kf7-g6 10.Sf3-e5+ Kg6-h5 11.Bb5-e8+ Pg7-g6 12.Bh6-g7 Bc8-h3
13.Pg2xh3 Bd1-g4 14.Pf2-f3 Kh5-h4 15.Pf3xg4 (2023-03-19, hidden) more ...
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Objective: co-record shortest achievement of task, followed by artistic continuation.
Henrik Juel: C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: 1.Pe2-e4 Pb7-b5 2.Pe4-e5 Pb5-b4 3.Bf1-b5 Pb4-b3 4.Sg1-e2 Pb3xc2
5.O-O Pc2xb1=S 6.Qd1-c2 Pf7-f5 7.Qc2xc7 Ke8-f7 8.Qc7-c4+ Pd7-d5
9.Pe5xd6ep+ Kf7-f6 10.Qc4xg8 Bc8-e6 11.Pd6-d7 Qd8-c8 12.Pd7-d8=S Sb8-d7 (2023-03-19, hidden) more ...
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Objective: co-record shortest achievement of task, followed by artistic continuation.
Henrik Juel: C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: 1.Pd2-d3 Pe7-e5 2.Sb1-d2 Pe5-e4 3.Sd2-f3 Pe4xf3 4.Pb2-b4 Pf3xe2
5.Bc1-a3 Pe2xf1=S 6.Qd1-g4 Ke8-e7 7.O-O-O Ke7-d6 8.Pb4-b5+ Pc7-c5
9.Pb5xc6ep+ Kd6-c7 10.Qg4xd7+ Kc7-b6 11.Pg2-g4 Sf1-g3 12.Ph2xg3 (2023-03-19, hidden) more ...
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Objective: record achievement of task. Promotion can be to either minor officer, but prefer to keep the "stem cell" to avoid arbitrary choice of non-standard material.
Henrik Juel: with wSd8 C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: with wSd8
1.Pe2-e4 Sg8-f6 2.Ke1-e2 Sf6-d5 3.Pe4xd5 Pg7-g5 4.Pd5-d6 Bf8-h6 5.Pd6xc7 O-O 6.Pc7xb8=S Qd8-a5 7.Ke2-e3 Pg5-g4+ 8.Pf2-f4 Pg4xf3ep+ (2023-03-19, hidden) more ...
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Objective: record achievement of task. Promotion can be to any officer, but prefer to keep the "stem cell" to avoid arbitrary choice of non-standard material.
Henrik Juel: with wSb8 C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: with wSb8
1.Pe2-e4 Sg8-f6 2.Ke1-e2 Sf6-d5 3.Pe4xd5 Pg7-g5 4.Pd5-d6 Bf8-h6
5.Pd6xc7 O-O 6.Pc7xb8=S Qd8-a5 7.Ke2-e3 Pg5-g4+ 8.Pf2-f4 Pg4xf3ep+ (2023-03-19, hidden) more ...
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Objective: record achievement of task. Promotion can be to any officer, but prefer to keep the "stem cell" to avoid arbitrary choice of non-standard material.
Henrik Juel: with wSc8 C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: with wSc8
1.Pd2-d4 Sg8-f6 2.Ke1-d2 Sf6-e4+ 3.Kd2-e3 Se4-c5 4.Pd4xc5 Pg7-g5 5.Pc5-c6 Bf8-h6 6.Pc6xb7 O-O 7.Pb7xc8=S Pg5-g4+ 8.Pf2-f4 Pg4xf3ep+ (2023-03-19, hidden) more ...
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Objective: record achievement of task. Promotion can be to either minor officer, but prefer to keep the "stem cell" to avoid arbitrary choice of non-standard material.
Henrik Juel: with wSd8 C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: with wSd8
1.Pd2-d4 Sb8-c6 2.Ke1-d2 Sc6-e5 3.Pd4xe5 Sg8-f6 4.Pe5xf6 Pg7-g5 5.Pf6xe7 Bf8-h6 6.Pe7xd8=S O-O 7.Kd2-e3 Pg5-g4+ 8.Pf2-f4 Pg4xf3ep+ (2023-03-19, hidden) more ...
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Objective: record achievement of task. Promotion can be to either minor officer, but prefer to keep the "stem cell" to avoid arbitrary choice of non-standard material.
Henrik Juel: with wSd8 C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: with wSd8
1.Pf2-f4 Pe7-e6 2.Pf4-f5 Bf8-c5 3.Pf5-f6 Sg8-e7 4.Pf6xe7 Bc5-b6 5.Pe7xd8=S Pc7-c5 6.Ke1-f2 O-O 7.Kf2-e3 Pc5-c4+ 8.Pd2-d4 Pc4xd3ep+ (2023-03-19, hidden) more ...
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Objective: record achievement of task. Promotion can be to either minor officer, but prefer to keep the "stem cell" to avoid arbitrary choice of non-standard material.
Henrik Juel: With wSf8, C+ Stelvio 1.0 (2023-03-19, hidden)
Henrik Juel: With wSf8
1.Pf2-f4 Pd7-d5 2.Pf4-f5 Bc8-d7 3.Pf5-f6 Bd7-c6 4.Pf6xe7 Sb8-d7 5.Pe7xf8=S Qd8-g5 6.Ke1-f2 O-O-O 7.Kf2-f3 Pd5-d4+ 8.Pe2-e4 Pd4xe3ep+ (2023-03-19, hidden) more ...
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