[Retros] Cooking a famous AP-problem?
liskov at im.bas-net.by
liskov at im.bas-net.by
Fri Jun 29 19:33:18 EDT 2007
I see no reason to revise the conventional treatment of AP
after Petrovic and to reinterpret the AP-study by Rinder.
In my opinion, extra arguments by Guus (and the application of
the PF-logic in the way that Guus proposes) are not convincing.
It is entirely B's responsibility to justify the (attempted)
forced e.p. key, W may well counteract him, and B fails unless
he manages to castle in all the lines (not manages by ANY reason:
destroyed castling, perpetuum checks, a premature mate, etc.).
Since the move R8a7+(??) destroys castling, it cannot help B to
justify e.p. and, thus, any further game after it is senseless
wrt to the key justification (regardless of a triple repetition,
a draw or not, etc.). [Here "??" marks illegal moves, including
ones that definitely make the whole line illegal.] Executing e.p.
restricts only B, not W; it's only a (forced) attempt to move.
Now two remarks apropos, on 50 moves.
I too don't know any AP-problem (type Petrovic) based on
the 50-moves rule. In the following problem
(V.Liskovets and A.Kornilov, 1981, "Schwalbe", h.69)
B-> (AP) Can Black win?
we succeeded only partially: a blockade of B's castling is
sufficient to disqualify the e.p. key; however, unfortunately,
W can further destroy castling.
As to automatic draw, let me quote once more (we discussed this
in January) Art.5 of Piran's Codex 1958:
"If the solution necessarily asks for more than 50 moves without
any capture, pawn-move or castling, the position is not a draw.
If provable by retroanalysis that one or more of such moves
directly preceded the solution and the total amounts to or
surmounts 50 moves, the position is automatically a draw."
Rol, Guus <G.A.Rol at umcutrecht.nl> wrote:
> Yesterday my brain must have been short-circuited for a while trying to
> sell you standard "AP type Petrovic" for the move turnover type "AP
> after Keym". Fortunately this doesn't affect the crux of the story but
> I'll correct it here for the sake of clarity.
> Guus Rol.
> (correction of yesterdays entry)
> Dear retro-friends,
> Another chapter in my discussion of retro-strategic principles
> is this famous problem by Gert Rinder. Now, I haven't voiced my concerns
> on the foundations of AP-logic here (yet) and I won't be doing so at
> this point. I'd rather focus on 2 aspects of this composition:
> (1) the post factum principle in the move choice for AP problems
> (2) how can the automatic repetition rule cook this problem - to
> create an even better one!
> Author: Gert Rinder
> Position: r2bk3/p1Rpp3/P1p2p2/KpP2P2/1P2p3/1P6/p7/8
> Author stipulation: Draw (AP type Petrovic)
> My stipulation: Black wins!
> Starting from the second aspect I suggest this solution: 1.cxb6
> e.p. (requiring justification) axb6+ 2.Kxb6 Pa1R 3.Kb7 R1xa6 4.Rc8
> (first time) R8a7+!! 5.Kb8 Ra8+ 6.Kb7 (second time) R8a7+ 7.Kb8 Ra8+
> 8.Kb7 (third time!); if you know PB-R309, you know what comes next. The
> position can't be considered a draw since there is no proof that the
> "same" position occurred thrice! Continuing play however - by whatever
> move, e.g. R6a7 mate - proves prior black castling right absolutely, and
> thereby proves the e.p. right a posteriori.
> Now there are several ways to argue against this approach - we
> don't want this automatic draw convention, it didn't exist at the time,
> this is a strange mix of AP and PF (not a good objection), etc - but all
> objections overlook the angle of having just created a beautiful new
> solution to a famous AP-problem. Not only does it contain all of the
> content of the previous one - the original solution becoming the try -
> but it adds a new element as well which is not readily available in most
> AP-compositions. I couldn't find another existing AP-problem cooked
> through this procedure, but I could find some that will be easily cooked
> by the 50-moves rule if it ever became rationalized and automatic. It is
> a characteristic trait of AP-problems that short AP-solutions can be
> affirmed or refuted by long "virtual" variants.
> Now back to point (1). In one of my previous posts I introduced
> the (rather arbitrary) concept of "game enforcers". This is a good case
> for demontrating what I mean by that. The principle behind game
> enforcement is that "a PF-solution continues under most conditions
> unless can be shown that it stops". One of the reasons is that PF
> implies that all choices from all "acceptable pasts" are available
> simultaneously. White may castle long if he can, he may castle short if
> he can - his choice is arbitrary even if the castlings are mutually
> exclusive. In Gert Rinders problem the question is the choice between 2
> pasts: (I) a past in which white is stalemated in the diagram (II) a
> past in which e.p. is legal and can be justified a posteriori. PF logic
> says he can chose either one of them and therefore must chose the one
> that will leave him a move. Stalemate is the absence of even a single
> option to move. PF-logic shows that the stalemate option need not be
> accounted for by retro-variants. So indeed, white starts and black wins
> in this composition.
> Note: I use the common descriptor PF here, but I'd rather use PA
> (Post Actum) for its major component. Left for another post.
> Guus Rol.
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