[Retros] MDR / promotion / fractional moves

[Rol, Guus]

Hi Roberto,

Your pretty formal approach to MDR hooks in quite nicely to the system I have developed for the formalization of "missing game state information" conventions. Look at these postulates:

(1) A diagram is preferably viewed as a position at the start/end of a full move. I call that the "dominant assumption". The dominant assumption is the one you must assume in play if it is legal in at least one proofgame for the position.

(2) A diagram can be viewed as a position with a move underway only if inevitable. I call that the "recessive assumption". No proof game may exist where the diagram coincides with the completion or start of a full move.

Of course, (1) and (2) are the opposite sides of the same coin and are only separated for clarity. The first one corresponds in form to the castling convention, the second one to the e.p. convention. Evidently, the standard forms for these extended conventions can only be derived from your premise that "the MDR definition ALLOWS a deviation but not forces it" which is not true for some of the Finzer categories. With the 2 new genre postulates, no further stipulations are needed to identify an "MDR-problem" amidst "full-move problems" which is ideal from the design viewpoint.

A further advantage of this postulate form is that it may be seamlessly tied in to aposteriori logic - where a fractional move assumption could overtake a full move assumption if justified a posteriori - or to retro-variant logic - with partial solutions linked to different fractional retro-moves. But this paragraph is probably just my dream!


Guus Rol.



-----Oorspronkelijk bericht-----
Van: retros-bounces at janko.at [mailto:retros-bounces at janko.at] Namens raosorio at fibertel.com.ar
Verzonden: woensdag 27 februari 2008 14:16
Aan: retros at janko.at
Onderwerp: [Retros] MDR / promotion / fractional moves


Hi Mario,

Many thanks for this very valuable mail. This is the type of help we need indeed: 
Antecedents. We knew the BG (Berührt - Geführt = Touched-Moved) one but not  the article you are commenting here.

Any additional help would be very welcome.

Yes,. I got the Finzer's problem from the PDB.

The MDR convention we are working on attempts to establish a general frame for all the retroanalyzable types of deviation from article 3 (Laws of Chess). These deviations are classified as,

- Opportunity: leaving its own king in check; using already lost rights
- Completeness: the move does not complete all it's parts.
- Sequence: the move does not respect the legal order of its partial actions 
   (promotion and castling)

We use "retroanalyzable" because the geometry of the move (complete or not)  respects the article 3. On the other hand, the MDR definition ALLOWS a deviation but not forces it. Then, an MDR problem has to build a proper scenario for a correct solution that makes the situation "retroanalyzable".

We identified 16 deviation cases for the orthodox chess. These include cases resulting from a complete and illegal move (as in the BG problems) and from a fractional move (legal or illegal, as in the Finzer's article). We established a simple hierarchy in the scale completeness- legality that makes possible all these types to coexist under the same convention with a clear criteria to determine the correct solution.

An example,

Jorge Lois & Roberto Osorio
5bBR/p1pppPpp/Pp4p1/1N6/8/P7/kPP1P3/1RK5
Is white forced to deliver mate?   MDR
b) wR from h8 to a8

A retro looking to the position shows that white is in the middle of a capturing process.
(other way,  black side would be retrostalemate). 

a) f7xRe8=... is being done, legal but not complete (1 part done, 2 undone). Then, according to article 4.6 the move has to be completed and it's mate despite of the type of piece it were promoted.

b) f7xRg8=... is being done, illegal and incomplete (2 parts done, 2 undone, illegal sequence). Then, a strange retraction (article 7.4) has to be made: to recover the position with the black rook on g8, but after that white is forced to capture this rook anyway (article 4.3, the rook was "touched").  To capture the rook white has to play f7xRg8=... but it's not committed at all to promote a bishop. So, the answer is no, since white is able to promote a knight.

This example illustrates my original point of "legal order of partial actions". A bishop promotion was clearly insinuated (half done) but there are no penalties. This is the most subtle case: a just formal illegality showing retroanalyzable traces.

Best,
Roberto Osorio