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MatPlus.Net  Forum General Yarosh's famous Babson (1.a7!) is illegal position |
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| | | (1) Posted by Geoffrey Caveney [Sunday, Sep 30, 2012 19:05] | Yarosh's famous Babson (1.a7!) is illegal position
Has it been noted before that Yarosh's famous Babson Task #4 with the elegant key 1.a7! is an illegal position?
FEN Bq1B1K2/3PpN2/P3Pp2/P1p2P2/2Pk1b1R/1p6/pN1P1P2/QR6
White has all 16 pieces, so Black cannot have made any captures. That means his Pa2 must have been his original a-pawn and stayed on the a-file. That means White's original a-pawn must have captured away from the a-file to clear the Black a-pawn's path, and the diagram's wPa5 and wPa6 must have captured onto the a-file from other files after the Black a-pawn advanced. So the original White a-pawn had to have made at least 2 captures to reach c4 in the diagram. The two current White a-pawns must have made at least 3 captures to move from the b- and c-files. That's 5 captures by those three White pawns.
The White d-pawn is on its original square. So the diagram's wPd7 must have made at least 1 capture. But if it came from the e-file, then the diagram's wPe6 must have made at least *2* captures, because the original White f-pawn is still on its original square. That accounts for all of White's pawns except his original h-pawn, which is on f5 in the diagram, which required 2 more captures.
Add up all the captures required by White pawns to reach the diagram positon: 10 captures. One can re-arrange which original pawns captured to which squares in the diagram (for example, the wPd7 could have made 3 captures and the wPe6 made none), but the minimum number of captures by White pawns cannot have been less than 10.
But Black still has 8 pieces and pawns on the board, so White cannot have made 10 captures in the game. Thus the diagram position is illegal.
Geoffrey Caveney
| | | (2) Posted by Geoffrey Caveney [Sunday, Sep 30, 2012 19:22] |
Correction: It is possible for the White pawns to have made only 8 captures, because the original White a-pawn could have captured to the b-file, then captured back to the a-file. The original White b-pawn also captured to the a-file, and the c-pawn did not capture. This reduces the number of captures from 10 to 8.
BUT there's still a problem: One of the 8 captured Black pieces and pawns was the original Black h-pawn. But none of the White pawns' 8 captures can have been *onto* the h-file. So the only way for this position to be legal, is if the original Black h-pawn *promoted earlier in the game* and then moved to another square to be captured by a White pawn. Thus the diagram requires a previously promoted piece, akin to a diagram with two Black queens.
Geoffrey Caveney
| | | (3) Posted by Joost de Heer [Sunday, Sep 30, 2012 21:11]; edited by Joost de Heer [12-09-30] |
White captured hxg, black promoted the h-pawn, and it later got captured by one of the white pawns, e.g. h3xg4 (...) h2-h1=R (...) Rh1-h5 (...) Rh5-f5 g4xf5
| | | (4) Posted by Geoffrey Caveney [Sunday, Sep 30, 2012 21:32] |
Yes, but that means the position requires a previously promoted piece. In your example, Black needed 3 rooks to reach this position. The 3 rooks might not have all been on the board at the same time, but they were there at some point in the game. To me, this seems to be in principle just as great a flaw as having 3 Black rooks on the board in the diagram position.
| | | (5) Posted by Ian Shanahan [Monday, Oct 1, 2012 06:34]; edited by Ian Shanahan [12-10-01] |
Previously promoted force ("obtrusive force") in a chess problem's proof-game, particularly if no longer present in the diagram position, by convention is never regarded as a flaw (unless retroanalysis is a feature of the problem, and maybe not even then!). If such force *is* present - e.g. bPb7 &d7, bBa4 - then this Bishop is labelled obtrusive, and in some circles it is still regarded as a flaw (though that convention seems to be slowly disappearing). Obviously-promoted force - e.g. bBa4 & a2 - is even more likely to be regarded as a flaw, except, perhaps, in the accomplishment of a task otherwise unachievable. The reason behind such thinking is that orthodox problems' proofgames normally have nothing whatsoever to do with a regular, combative games of chess.
Still, it's an interesting fact you demonstrate regarding Yarosh's Babson-task masterpiece.
| | | (6) Posted by Geoffrey Caveney [Monday, Oct 1, 2012 16:07] |
Thank you for the explanation Ian. I knew an obviously promoted piece was considered a flaw, but I didn't know a less obviously obtrusive piece (bBa4 bPd7 bPb7) might be considered acceptable. And I didn't know a previously promoted piece that was captured is considered fully acceptable. This expands the number of ugly positions I can use to achieve difficult tasks. :-)
| | | (7) Posted by Jan Hein Verduin [Monday, Oct 1, 2012 21:01] |
Actually, that there must have been a black promotion has been pointed out before; by (who else but?) Tim Krabbé and at least as early as in the Dutch magazine Schaakbulletin 192 (nov. 1983). Though afaik Krabbé didn't bother to mention this small blemish in his further publications about Yarosh's masterpiece, such as Chess Curiosities (1985) or the booklet De man die de Babson task wilde maken.
| | | (8) Posted by Jacques Rotenberg [Tuesday, Oct 2, 2012 01:02] |
Perhaps it means that Krabbe doesn't look at this as a blemish at all.
| | | (9) Posted by Ian Shanahan [Tuesday, Oct 2, 2012 07:15] |
Surely it is NOT a blemish?
| | | (10) Posted by Hauke Reddmann [Tuesday, Oct 2, 2012 14:45] |
The opinions on the matter are surely divided (a well know example is
in the Brunner book where Kraemer and Zepler spot an obtrusive piece;
Kraemer doesn't care at all, Zepler does care and constructs it away -
or was it the other way round?), but to my best knowledge the vast
majority of editors reacts about this...
Illegal position: "Oh joy, the reciprocal dingbat cycle can be shown
at all. Well, not in MY journal. Make a short communication on the
theme, but keep it out of my informal! And send it to Hauke, he might
do magic!"
Promoted force: "Oh joy, the reciprocal dingbat cycle can be shown
at all. Since it's so hard a theme, I show it in my informal, maybe
some judge awards you a Special Prize. And send it to Hauke, he has
cracked tougher nuts than this!"
Obtrusive force: "Oh joy, the reciprocal dingbat cycle can be shown
at all. The obtrusive bishop is a shame, but I guess we still know a
prize bearer of this years Informal. If you want to be on the safe side,
though, send it to Hauke who constructs it away in a hour."
Invisible retro force: "Oh joy, the reciprocal thingamajig cycle can be
shown at all. I take it in for the next issue. 1st Prize is practically
guaranteed. Bit clumsy, though, you even need a promotion in the proof
game. Would have suggested that you send it to Hauke who surely will
spot the crucial pawn that can be hacked off in a minute, but he is too
busy fighting with the reciprocal dingbat cycle."
Hauke (firmly tongue-in-cheek :-)
| | | (11) Posted by Ian Shanahan [Wednesday, Oct 3, 2012 09:00]; edited by Ian Shanahan [12-10-03] |
Having read many books and magazines over the past three decades devoted to chess composition, I'm yet to see ANY discussion of promotion in an orthodox problem's proof-game where the promotee has been captured prior to the diagram position - let alone a criticism of it. It seems to be a non-issue. Indeed, I can see no logical reason why it should matter (unless retroanalysis is somehow important or thematic - in which case, such promotion could well be an advantage!)
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