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 CHESS SOLVINGTournamentsRating lists1-Apr-2021

MatPlus.Net Forum General Proof games ended by the laws of chess

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### Proof games ended by the laws of chess

Proof games almost always end in an ambiguous state, with pieces scattered about. However, whether with a special stipulation or not, the final positions can be determined as the final one. Checkmate, stalemate, repetition, dead position, insufficient, 50-move rule are the main categories.

The longest unique PG ending in checkmate that I know of is https://pdb.dieschwalbe.de/P0002187.

Michel Caillaud, Die Schwalbe 10/1983, 1st Prize, PG in 38.5
(= 16+16 )

Apart from checkmate, this seems to be a faintly explored subsection of proof games.

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There are proof game problems where, given the move-count and the fact that the game is drawn, the proof game can be uniquely determined, the diagram position having just arisen for the third time. Andrew Buchanan has composed some such, for exacmple the PG 9 https://pdb.dieschwalbe.de/P1298076 and the PG13 https://pdb.dieschwalbe.de/P1338392. Guus Rol composed the PG41.5 https://pdb.dieschwalbe.de/P1011937 -- an extraordinary PG ending with 2 occurrences of a sequence of 12 full moves.

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Several years ago someone posted a challenge on the retros list to find the shortest proofgame for positions ending with a specific mating move. A lot of possible final moves were covered, as far as I remember.

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MATE
There are about 250 orthodox checkmate PGs in PDB. Joost has just reminded us that there was a shortie checkmate craze a few years ago - they must surely be in WinChloe if not RML, but not PDB. Some were quite slick if I recall.

PAT
Stalemate is challenging for PGs because it requires global domination, not just a lethal assault on the king. I can find 6 in PDB: https://pdb.dieschwalbe.de/search.jsp?expression=PROBID%20IN%20%27P0001605;%20P1003999;%20P1004002;%20P1004131;%20P1004135;%20P1066775%27

3REP
https://pdb.dieschwalbe.de/search.jsp?expression=k%3D%27unique+p%27+and+k%3D%27draw+by+rep%27+and+not+cooked gives 12 PGs ending in 3Rep by Olin, Frolkin/Tkachenko, Buchanan, Rol, Le Gleuher. These all have a constraint of some kind, which is probably essential to this kind of game end.

INSUFFICIENT MATERIAL
There are a number of massacre PGs which end with insufficient material for checkmate. This immediately triggers game end of game by DP rule, but there's no surprise: because no solution exists in which the last move was not a voluntary capture of the last mating unit. The most famous of these is Francois Labelle's stupendous bare king https://pdb.dieschwalbe.de/P1235533 PG 19.5. There are six other sound ones in PDB with 3 pieces, by Wilts/Geissler, Labelle & Bachmann: https://pdb.dieschwalbe.de/search.jsp?expression=PROBID%20IN%20%27P0000284;%20P0005395;%20P0005400;%20P0005401;%20P1013074;%20P1017484%27 Another 1998 problem, https://pdb.dieschwalbe.de/P0005399 would potentially be rendered unsound by the 1997 Dead Position rule, but the Codex only included the rule in 1999!

DP
Some other Labelle massacres are only sound *because* of DP rule: https://pdb.dieschwalbe.de/search.jsp?expression=PROBID%20IN%20%27P1281143;%20P1281145%27
I want to point out a fairy PG that takes advantage of obligatory draw by repetition: https://pdb.dieschwalbe.de/P1281158. I've never seen any other Circe problem which uses this mandatory looping, which is easy to achieve with Circe at any point in the game.

50M
Finally, right now there are *zero* PGs in PDB which take advantage of 50 move rule. Not even a fairy one.

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Just to mention, I do not agree that P0005399 is rendered 'no solution' by the DR rule. This is help play, with the diagram position as the target, the concept of checkmate is meaningless - unless you try to reach the diagram via a game that enters and leaves checkmate.

Logically, in PGs DR means any move that makes it impossible to reach the target position. So if you target the basic position of the Ruy Lopez, then 1.d4 is DR. Every solver uses this even without knowing about DR...

But DR can be used in SPGs as an additional rule, at least theoretically. You can think of a SPG which has two solutions without DR, but with it, only one, because the other is DR too early.

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(6) Posted by Joose Norri [Saturday, Jun 5, 2021 13:12]

Ah, I overlooked the last Labelle. Well, I do not agree. I consider it correct only with the addition 'DR in effect' or something similar.

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MatPlus.Net Forum General Proof games ended by the laws of chess