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MatPlus.Net Forum General Chess960 problems?
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(21) Posted by Andrew Buchanan [Monday, Apr 23, 2018 20:29]; edited by Andrew Buchanan [18-04-28]

Hi Joost,

For (1), h#4 would mean white starts and black delivers mate on his first move, since the conventional party (black) doesn't have the first move. So it should be h#3.5.

The "official joke", Art. 15 isn't anything to do with half-duplex. The player to mate remains the same. In the adversarial genres (d#, s#), the opponent gets an extra single move. In h#, Black loses his first move so it's really set play with no actual play.

However, I agree it's best here as h#3.5, for reasons given.
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(22) Posted by Siegfried Hornecker [Tuesday, Jun 12, 2018 06:03]

(= 16+16 )

SH, original
Chess960, SPG
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(23) Posted by Petko Petkov [Tuesday, Jun 12, 2018 09:18]

This is not a legal position according to the rules of Chess-960! Pay attention to one important rule in chess-960: The king must be placed on a square between the rooks!
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(24) Posted by Frank Richter [Tuesday, Jun 12, 2018 12:48]

I assume, this isn't a starting position, but an end position of a virtual game ... ("SPG")
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(25) Posted by Petko Petkov [Tuesday, Jun 12, 2018 14:15]

But perhaps there is something unclear!?
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(26) Posted by Petko Petkov [Tuesday, Jun 12, 2018 16:04]

If the starting position is SQRBBKRS possible is 1.Sh1-g3 Sa8-b6 2.0-0 Qb8-a8 3.Kg1-h1 Rc8-b8 4.Rf1-g1 Sb6-c8 5.Sg3-f1 dia therefore SPG 4,5 (if the white castling is not possible on the first move - in this case there is a dual after 1.0-0).
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(27) Posted by Siegfried Hornecker [Wednesday, Jun 13, 2018 06:19]

You solved it correctly. Yes, I didn't see that dual.
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(28) Posted by Andrew Buchanan [Saturday, Jun 16, 2018 18:44]; edited by Andrew Buchanan [18-06-16]

This is sound, but no longer than the previous one.
(= 16+16 )

Original SPG Chess960
C+ Jacobi
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(29) Posted by Geir Sune Tallaksen Østmoe [Friday, Aug 24, 2018 22:00]

Thanks for all your replies to my original question! Since then, I have composed and published a little Chess960 study.

Geir Sune Tallaksen Østmoe
Aftenposten 2018
(= 5+3 )


1.c5 Bxd7 2.0-0-0! Kf8 3.Rxd7! Rxd7 4.c6 Ke7 5.b7 wins.

In standard chess, 2.Rd1 with the same idea would have worked, but here this fails to 2...0-0-0! White has to play 2.0-0-0 so that Black can no longer castle.
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(30) Posted by seetharaman kalyan [Saturday, Aug 25, 2018 20:09]

I thought in Chess 960 the king still moves two squares only to castle... so for 2. ooo won't the king will move to e1 and the rook to f1.
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(31) Posted by Kostas Prentos [Sunday, Aug 26, 2018 01:48]

The castling rules in Chess960 are (have to be) special. Check the following link for details:
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(32) Posted by Andrew Buchanan [Monday, May 11, 2020 13:05]

I thought we must have already found the longest "APS/ASP/PAS/PSA/SAP/SPA" Chess960 SPG. But apparently not!

(= 16+16 )

(16+16) Chess 960 SPG
C+ Jacobi

Paradoxically for a Chess960 position, this is symmetrical. Normally since we don't know the starting position, we would have different line-ups for White and Black to force a common starting array. But not in this one! :-)
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(33) Posted by Siegfried Hornecker [Monday, Jun 1, 2020 16:46]; edited by Siegfried Hornecker [20-06-01]

(= 6+5 )
(version: (= 6+4 )
SH, Original
After Rafael Kofman
White retracts one move, then checkmates in exactly 2 moves.

White retracts 1.0-0 (Kf1, Rg1). Retracting this move, however, does not prove that the castling was actually a legal move, so White plays 1.0-0. Black has no defense against the checkmate next move, as by castling White proved that the king started on f1.

In the version, there is a try that fails only because retracting the castling wouldn't prove it is actually legal. But I think that is not how the Codex works anymore?
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(34) Posted by Andrew Buchanan [Tuesday, Jun 2, 2020 03:46]; edited by Andrew Buchanan [20-06-02]

Hi Siegfried,

Without examining your problem in detail, here's my understanding of the conventions. Let's put Chess960 down for a minute.

(1) The castling & en passant conventions apply only to forward moves, in the context of other possible retro deductions about the history of the game. The castling convention is "optimistic" - by default "yes you can"; while the en passant convention is "pessimistic" - unless you can prove the last move was the double hop "no you can't".

(2) In general retro problems (e.g. "Last move?") you have to prove everything about the history of the game. The conventions don't apply at all. You can't just randomly retract something because it might have been the last move, whether or not it's a conditional move. If you prove that the last move can only have been a certain conditional move, then by that logic, the game state must have been such so that the move could have been played.

(3) Retractors are different again. *Any* legal or possibly legal last move may be retracted, without recourse to the conventions. This may have specific consequences to the game state. So in particular if you retract an e.p. move, then the prior move can only have been a double pawn hop. This is an essential trick in adversarial retractor stipulations. Similarly, if you retract castling, then it is *certain* that from the position arrived at, castling is legal. You don't have to castle again to "prove it".

So how do these apply to Chess960? There is no explicit mention of Chess960 in the Conventions yet. As earlier discussion in this forum explored, there are really *two* aspects of castling game state frequently conflated:
(a) position of K & R in initial game array,
(b) whether these pieces moved earlier in the game.

Let's see how they will be treated in the three cases listed above. Cases (2) & (3) are easy.
Case (2) in a general retro, universal pessimism applies. You must prove everything before being able to conclude what the last move was.
Case (3) in a retractor (as here) universal optimism applies. You can retract anything possible.
Case (1) is the most complicated, but I will state it for completeness. We can clearly apply the usual conventions for part (b). Castling is optimistic, en passant is pessimistic. For simplicity, it seems that people apply the same "optimistic" convention to part (a), although people should be aware that this involves a much greater degree of optimism!

The final point is that the help-retractor stipulation is a hybrid. There is a retraction phase, and then there is a forward phase. What happens? Well we begin with case (3), and then following the retraction, we have some knowledge of the game state, which will constrain forward moves. Any *residual* uncertainty (e.g. is some en passant move ok?) in theory would be addressed by case (1). That refinement isn't needed here, but that's how it works.

As far as I know here is no site where the above explanation of conventions is given. In its absence, every person interested in serious non-Smullyan retro has to struggle through and figure it out for themselves. The Retro Corner might have been such a place, and might still be again if an energetic editor can be given write access to clean it up (and put a new coat of paint on, it's a bit drab!)
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MatPlus.Net Forum General Chess960 problems?