[Retros] Favour/En Passant

Mon Jun 16 07:17:21 EDT 2014

Guus,

OK, that explanation of yours was needlessly confusing (as if to delay your
straightforward answer, knowing that it will not be considered correct)...

There obviously exists a #1, in two parts -- exactly as Andrew described --
if you accept that Partial Retro-Analysis is the default (and the Codex
does explicitly say that Partial Retro-Analysis is the default method to
resolve such a problem).

So, please explain your position, in simple terms (without this talk of
conventions and rules and digital boards, etc)...
Or, give me a reason I should want to disagree with the obvious
interpretation of the Codex.
Or, show me a problem where the Codex interpretation becomes ambiguous.

Why should I want to believe that there is no mating move (by one of two
e.p. captures) in the diagram?
Why should I want to believe that stalemate of white would alter this?

You have completely lost me.

Best,
 Kevin.

On Mon, Jun 16, 2014 at 3:58 AM, Andrew Buchanan <andrew at anselan.com> wrote:

> Guus,
>
>
>
> I disagree again with your main point.
>
>
>
> First, I do agree that Jonathan’s diagram is an excellent case. But I
> think it’s handled adequately by the existing conventions. It is not an
> issue nor a joke.
>
>
>
> Before the recent changes to the conventions driven through by Werner
> Keym, under the en passant convention the diagram would have no *permitted*
> mating move. That’s fine. The sky doesn’t fall apart. Even if there was no
> other legal move for White, this doesn’t put White in stalemate. Stalemate
> is the result of having no legal moves. It is **not** the result of
> having no permitted moves.
>
>
>
> It’s not a crisis: the sky doesn’t fall. We just admit the fact that in a
> few diagrams, it is not possible to determine whether certain en passants
> are allowable, and indeed whether the game is over or not. Those are
> interesting diagrams, and it’s certainly not worth twisting everything in
> order to ensure that some en passant must be allowed. That would be
> horrible.
>
>
>
> Under the PRA convention, which now applies by default, things are even
> more straightforward. The problem splits into two parts, according to
> possible histories. Each history allows one en passant, so the problem is
> solved. I believe that Werner Keym would say that the problem has 1
> solution, in two parts. I don’t particularly like PRA in this context,
> because it excludes any history in which neither e.p. is allowed. That just
> makes things too easy: most of Jonathan’s work is about showing that
> Black’s last move must have been one of the double hops. This is rendered
> irrelevant by PRA. However, PRA is not the main point.
>
>
>
> I think our main disagreement is coming clearer. Once again you are mixing
> together rules and conventions. My position remains that just because the
> conventions don’t **permit** us to play a certain move should have no
> impact at the level of the rules themselves.
>
>
>
> I made the next point in an earlier email, but I don’t think I got it
> across to everyone so I will say it again.
>
>
>
> If rules and conventions operate at the same level as you propose, then *
> *every** help pat is unsound, because the players are constrained by
> convention (i.e.: the definition of mandated player behaviour in a help
> pat) to work with one another to reach stalemate. Alternate lines of play
> which do not end in a stalemate are irrelevant, because the players are not
> permitted to play moves that diverge from the solution. So A1.3 kicks in
> right at the start. Similarly, **every** direct pat is unsound. White is
> bound by convention to eschew any path that can avoid a stalemate, and
> despite Black’s best efforts, the composition must end in a pat. Hence A1.3
> will kill the solution right from the start.
>
>
>
> Now the issue here, I submit, is not A1.3, but the mixing together of
> rules and conventions. Please let’s distinguish the rules from the
> conventions, and say the rules are about legality, while the conventions
> constrain which legal and possibly-legal moves are permitted, then we do
> not get in the horrible confused state that you are proposing.
>
>
>
> And I don’t even believe that your planned path makes it easier to scale
> to fairy compositions. I think the idea of rules (including fairy rules)
> addressing legality, and conventions (including perhaps fairy conventions)
> then determining permissibility, is a bedrock upon which we can build a
> solid artifice.
>
>
>
> Thanks,
> Andrew.
>
>
>
> *From:* Retros [mailto:retros-bounces at janko.at] *On Behalf Of *Guus Rol
> *Sent:* 16 June 2014 17:33
>
> *To:* The Retrograde Analysis Mailing List
> *Subject:* Re: [Retros] Favour/En Passant
>
>
>
> Dear Jonathan,
>
>
>
> Excellent case and a real issue. There are many similar situations,
> particularly in fairy land like with the "fuddled men" in Turnbulls
> infamous article. I had preseved the treatment of these cases for an
> "advanced topics" post but I can outline it here. You could have made
> things a little worse by making sure that white was "stalemated" apart from
> playing the e.p. moves. Deciding that white is stalemated would be illegal
> as there would exist no proof game leading to stalemate. Clearly some e.p.
> move must therefore be permitted.
>
>
>
> The reduction principle on the DGCs is based on the premise that some
> preferred option for play remains but such is not always the case. Besides
> that, there is the possibility of a "group right", a right that cannot be
> proved for each individual member of the group but van be proved to exist
> somewhere in the group. The handling of the cases occurs on a higher level
> than the handling of the DGC-set / Game set.
>
>
> *The natural approach is the temporary promotion of all "secondary rights"
> to "primary rights" (I am not sure about this terminology yet but you know
> what I mean)  in a "rights group" allowing each one the be executed as such
> - i.e. as if it were a right to castle. After this promotion, the reduction
> from DGC to Game resumes with the modified "rights".*
>
>
>
> One issue remains and is reflected by your example. Do you wish to allow
> "promotion" only when no other playing option remains or do you wish to
> allow it whenever a group right exists  - as in your example? There is an
> aspect of personal taste in this choice, but also one of best workability.
> Having contemplated this for a while on the basis of fairy forms, my gut
> feeling is that it is best to stick with the first choice. Which means that
> white cannot play e.p. in the example you presented.but he could if he were
> stalemated (or mated) otherwise. But you are entitled to disagree since the
> choice steps outside the necessities of a a sound and consistent
> decisioning system.
>
>
>
> Note: On top of the retro-decisionig-tree is the 1st command: *There must
> always be a proof game*.
>
>
>
> Best wishes, Guus Rol.
>
>
>
>
> On Mon, Jun 16, 2014 at 10:22 AM, A J Mestel <ajm8 at maths.cam.ac.uk> wrote:
>
> Now that I'm connected again, I'll repost something I wrote a month ago.
> It feels a bit like a poor joke, which had some point at the time, but
> loses everything in the re-telling, but still, here it is/was.
>
>     Jonathan
>
> Date: Fri, 6 Jun 2014 11:04:56 +0100 (BST)
> From: A J Mestel <ajm8 at maths.cam.ac.uk>
> To: The Retrograde Analysis Mailing List <retros at janko.at>
> Subject: Re: En passant
>
> Did this ever get posted in the list? I never saw it, and got no replies.
> It's a bit dated now, but someone said that en passant was only legal if
> you could prove what the previous move had to be etc. Needs to be a bit
> more precise.
>   Jonathan
>
> On Wed, 28 May 2014, A J Mestel wrote:
>
> Someone must have done this before, but consider:
>
> W: Kc5 Rd8 Bc8 Nc6 a5 a6 e5 e6
> B: Kc7 Bb8 b5 d5
>
> Can White mate in one? Not according to the definition I read here a few
> mails ago.
>
>
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