[Retros] Favour/En Passant

[Guus Rol]

Hi Kevin, Andrew and Jonathan,

Actually I fully agree that pRA is the default assumption and resolves the
issue.

In fact, this is so obvious that I haven't even considered this to be
Jonathans case. The logics are by nature a dimension separate from the
basic conventions in the sense that they can be an independent part of the
stipulation. In the old days I needed to write "pRA" if I didn't like the
idea of my problem being resolved by RS. Today I need to do the reverse,
namely add "RS".if such is what I desire. I have taken Jonathans example as
one to be resolved under the "RS stipulation" and I answered it in this
fashion.

You can take that as a general context for my theory. Most interesting
situations arise in RS and AP logics. In the pRA and retro-vairant logics
all retro-active issues are compressed at the entrance gate. Though they
are not at all obvious - especially in fairy forms - it is clear that all
is plain sailing after the initial conditions have been established.

Andrew and I will continue to diagree on the nature of conventions. I have
written 1 post about that and will write 1 more to address the precise
delineation (as I see it). Everyone can decide for himself which side he is
on.

Note: An essential characteristic of RS-logic is that things are different
in the solver domain than in the player domain. You may be able to prove
that you can mate in 1, but not be able to execute it under RS logic. See
my PB R309. One can prove that white can mate in either 5 moves or 8 moves
(in pRA style), but under RS logics it can only be done in 7 moves. The
reason is that RS-logic fuses variants from different proof games. But I
will write much more about that

Best wishes, Guus Rol.

On Mon, Jun 16, 2014 at 12:58 PM, 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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