# [Retros] Variables

Eric Angelini Eric.Angelini at kntv.be
Tue Nov 25 05:42:52 EST 2008

NOT :

à priori
à posteriori

BUT

a priori
a posteriori

... as this is latin !
(and not french)

Best,
É.

-----Message d'origine-----
De : retros-bounces at janko.at [mailto:retros-bounces at janko.at] De la part de Rol, Guus
Envoyé : mardi 25 novembre 2008 10:13
À : The Retrograde Analysis Mailing List
Objet : Re: [Retros] Variables

It is always hard to argue with an inventor considering his prerogative to set the rules. Nevertheless it must be noted that there appears to be a basic misunderstanding of the inventor regarding "notation systems". Starting from the real world, the "Variable Piece" is easy to implement. Take a undistinguished piece of white or black wood, write VP on it and put it on a chess board. With the game or solution underway the reduction of its possible roles can be scribbled in the wood, "it is now not a rook", "and not now a bishop either" etc. However, when executing a move with the VP you must show precisely what the chosen action entails. If it deletes another entity, the entity must disappear, en passant or otherwise. The function of a notation system is to identify the precise action that has taken place on the board in the real world. Apparently the inventor is not happy enough with his variable pieces, when he adds to it a mysterious use of the notation system in order to protect to VP mysteries. If we follow the thought line of the inventor we might as well decide to use an even shorter notation like Vb6, only identifying the target square and creating even more mystery on what VP to move to b6. Actually, even in standard chess I can create à posteriori justifications by using underdetermined notations. But frankly, must we take serious a solution which correctness does not depend on what you execute on the board but on the notation system you use?

Yes, it is possible to have different understandings of the à posteriori concept. From a science philosophical viewpoint one might even consider PF-logic as à posteriori. Nevertheless there is a restriction pertaining to the redundancy of terminology. If a proper analysis shows that "the a.p. justification of the e.p. move" is nothing but the combination of a clever notation trick and standard "proof it by doing it", than the assignment of the "à posteriori" qualification amounts to nothing but the suggestion of content that isn't really there. My current intuition is that the à posteriori identification of the two Pawns involved in the e.p. move is no different from the à posteriori "coming out" of a Queen identity 23 moves after its disguised appearance as a VP.

Guus Rol

--------------

In the given diagram, Vb2-b4 Vc4-b3 could be Rb2-b4 Bc4-b3 too (and if the position was totally different, it could also mean Pb2-b4 Kc4-b3, or
Qb2-b4 Qc4-b3).

To quote from the article:

"In fact, Tadashi[ Wakashima, the inventor of Variables, JdH]'s intention is that the moves should be written as 1. Vb2-b4 Vc4-b3. As this is compatible also with 1. Rb2-b4 Bc4-b3, it cannot simply be asserted that capture has taken place; only departure and arrival squares can be claimed. If c4 was a P (or a V that has already been shown to be a P), then c4-b3 is consistent only with ep capture."
[...]
"The same justification must be made for promotions; in C [wVe1 wVh1
wVh7 bKg7] one cannot claim to play h7-h8=S, but instead 1. Vh7-h8 only (note that this shows the wVh7 to be a pawn); the particular promotion must be justified by later play. And Ve1-g1 is not sufficient to justify this move as OO; but if followed by Kg7-g6 the alternatives Re1-g1 and
Qe1-g1 are ruled out leaving only OO, so we know that g1=K and Vh1 is now on f1 and is a rook."

As I said before, don't confuse Variables AP logic with retro AP logic.
For variables, later moves can be used to rule out possibilities, or to (re)move pieces that aren't directly affected by the variable move itself. The AP terminology is used in the latter sense.

Joost
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