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MatPlus.Net Forum Retro/Math What's the best white can do?
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(1) Posted by Guus Rol [Sunday, Nov 29, 2020 23:18]

What's the best white can do?

(= 4+7 )

(= 4+7 )

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(2) Posted by Joost de Heer [Sunday, Nov 29, 2020 23:47]

a) Claim a draw. If the claim is rejected, mate in 3.
b) Mate in 2.
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(3) Posted by Rewan Demontay (Real Name: James Malcom) [Monday, Nov 30, 2020 07:19]

What's the joke? An en passant "key" nor board rotation seem to be applicable under Joost's solutions.
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(4) Posted by Guus Rol [Monday, Nov 30, 2020 09:13]

Actually, Joost's answer is a very clever one and shows he sees the issues! The detail is that the rules do not require us to claim a draw in these situations, we merely declare it. Otherwise a lot of claiming would be going on in many of Andrew's problems!
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(5) Posted by Guus Rol [Monday, Nov 30, 2020 09:14]

@RewanDemontay: You're not there yet; it's no joke problem!
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(6) Posted by Siegfried Hornecker [Monday, Nov 30, 2020 09:14]

Diagram 1:
Draw. It can't be proven that Black played g7-g5+, the pawn could come from g6. If the pawn was on g6, Black could have played Qg1-e3 instead.

Dragram 2:
White can take en passant, which is easily proven. If he could not take en passant, the game would have been "dead" before the black g6-g5+ already, as any possible continuation would end in a draw.
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(7) Posted by Guus Rol [Monday, Nov 30, 2020 09:23]

Siegfried gets full marks!
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(8) Posted by Guus Rol [Monday, Nov 30, 2020 09:26]

This was my attempt at the "myth of the en passant key ..." but I couldn't get to a miniature so I decided to make a twin.
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(9) Posted by Hauke Reddmann [Monday, Nov 30, 2020 09:45]

Siegfried, that's no explanation for the retrodumb, also,
White can't "claim", it's automatic ;-)
So, here my more elaborated attempt:
Position Rg1: 1...g6-g5 is not even illegal, it's impossible!
The position is dead already after Qd2+, thus the position
Rg1+no ep rights (remember, a position is incomplete without
giving ep and castling rights) is illegal.
Position Qg1: As Siegfried said, since Qe3 and play can go on,
g6-g5 was possible and White can't prove he can capture ep.
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(10) Posted by Guus Rol [Monday, Nov 30, 2020 09:51]

Actually, Andrew might take issue with declaring the first diagram dead because it isn't CERTAINLY dead - similar to not accepting a checkmate because a possible e.p is still in the picture. Joost might have reacted on the same line of thought. By playing one more move (Qxg5+) we arrive at a certainly dead position which would draw before the stalemate!

I do not subscribe to Andrew's theories but there is a real issue here. Since the draw outcome under all assumptions is the same we can delay the discussion to a more suitable moment.
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(11) Posted by Guus Rol [Monday, Nov 30, 2020 10:02]


"impossible" and "illegal" are often used interchangeably in this context; I make no point of it.

The second diagram is legal because a legal proof game exists. In that proof game black's last move was g7-g5 (not g6-g5 for the reasons you gave). As there are no proof games without the last move g7-g5, white has the absolute right to play e.p.
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(12) Posted by Hauke Reddmann [Monday, Nov 30, 2020 10:08]

@Gus: My theory to the diagram is:
Either it is legal and ep or illegal because of dead.
Since a problemist knowingly giving illegal diagrams
and not warning "joke" will get no presents tomorrow :-),
only #1 remains.
I can make a practical experiment and ask the main
referee of Germany. :-))
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(13) Posted by Guus Rol [Monday, Nov 30, 2020 10:15]

@Hauke: There is nothing I disagree with here. So we end up playing e.p. in diagram 2 just as Siegfried suggested. What's the disagreement or is there just a misunderstanding?
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(14) Posted by Hauke Reddmann [Monday, Nov 30, 2020 10:25]

No disagree or misunderstanding, but I wanted to
proactively choose side when it comes to
Ragnarök^W* WWII over retro conventions -
I know WWI only from history files :-)

* cf. Amon Amarth, "Death in Fire"
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(15) Posted by Guus Rol [Monday, Nov 30, 2020 10:38]

I acknowledge the retro conventions in general but there are white spots (e.g. see my note about what Andrew might say) and there are complicated interactions. Won't try to fool you on "the rules" (without warning :-))
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(16) Posted by Joost de Heer [Monday, Nov 30, 2020 11:56]

The first diagram is a Schrödinger diagram: it's both dead and alive at the same time, until you open the box which hides the last move.
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(17) Posted by Guus Rol [Monday, Nov 30, 2020 12:01]

Right, it's the cat! The retro-logics (except PRA) are a posteriori. Reality depends on the state you observe when you open the box.
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(18) Posted by Andrew Buchanan [Monday, Nov 30, 2020 13:18]

I agree with Guus & Siegfried - and mostly with Joost.

R: 0. ... g7-g5+ or 0. ... g6-g5+.

(b) (first because it's simpler) If 0. ... g6-g5+ then it was the only option. e.p. is off, and the follow-up would be mandatory 1. Qxg5+ Rxg5=. So the game already died before Black's last move. Therefore Black played 0. ... g7-g5+, which was again mandatory. E.p. is on, and White has the alternative 1. fxg6ep+ forcing Kxg6 with option 2. Qxg5# So the position is #2.

(a) If 0. ... g6-g5, then there was the living option 1. Qg1-e3 instead, so it was perfectly plausible. In this case, the position is dead, as 1. Qxg5+ Rxg5= would be mandatory next stage. If Black just played 0. ... g7-g5+, then there is #3 1. fxg6ep+ 1. ... Qe3 2. Qxe3+ Kxg6 3. Qg5#. Either is possible. Having squeezed all the possibilities from the rules, we *then* go to the conventions to adjudicate. The regular ep convention resolves the doubt by saying that we can assume it wasn't played, so the position is dead.

The position is no more and no less "Schrodinger's cat" than any position where we can't determine whether e.p. is on. That's what the basic conventions are for.

Right from the start with DP, I was interested in exploring the implications of the rule directly, without needing recourse to the conventions. Interactions with the conventions might be an additionally complicated area to explore later perhaps, but it turned out that I have not yet exhausted the possibilities of the simple DP rule itself. It also seemed that there were unsettlable and therefore extraordinarily boring questions about whether the DP rule could have visibility of the conventions. I decided arbitrarily right from the beginning that in the problems I create, it doesn't have such visibility. I suspected that there would be some boring discussions that some people would nonetheless insist on having about the relationship between DP rule and the conventions: that some people would be certain it had to be one way. If the chess in a problem justifies one position on the matter or the other, then that seems great for the scope of that problem. I certainly have seen some beautiful such problems, going one way or another. Since the conventions are so vaguely drafted, one can have it either way, so why shouldn't we have it both ways?

I am just an idiot, but let me quote a smart person's words. Richard Feynman on "Rules of Chess". This is all good, but the actual quote I want is from the public comments:

"I will tell you about quantum electrodynamics without math, so my explanation will be necessarily incomplete. But I promise that my simplified explanation will not tell you anything that I would need to retract in a more detailed explanation."
~ Richard Feynman, opening a Cornell University on QED for a general audience.

That's what I would like for a retro theory, including DP. Something basic which does not need to be retracted when we have a complete theory that applies to very complicated fairy conditions and all the other stuff. That basic set of ideas should be expressed through Smullyan-style concrete examples, without confusing allusions to three different kinds of logic etc, etc.

Thanks so much: I love you all
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(19) Posted by Guus Rol [Monday, Nov 30, 2020 14:04]

That's a great quote! And I guarantee you I intend it to apply to everything I write - either in simplified form or in the full monty. My motto is Einsteins similar quote: “Everything should be made as simple as possible, but no simpler” (because then you would have to retract it later as per Feynman).

What you write about Joost and Schrödinger's cat is relatively true. It applies indeed to every uncertainty in retro-states, not just limited to this diagram or e.p. in general. Nevertheless, it is valuable to recognize the distinction between two fundamentally different approaches to resolving retro-uncertainty: one analytical by conditional histories (PRA) and the other one a posteriori by observing retro-state manifestation (opening the box) during a solution (RS and AP). I think that thought just occurred to Joost but he may correct me.
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MatPlus.Net Forum Retro/Math What's the best white can do?