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MatPlus.Net Forum Internet and Computing Nalimov and castling/ep
 
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(1) Posted by Hauke Reddmann [Thursday, Jan 25, 2018 15:00]

Nalimov and castling/ep


Evidently it's not implemented - Ke1 Ra1, Kd8 Rb2 is the standard example. (See e.g. http://horizonchess.com/FAQ/Winboard/weaktablebase.html)
What is the lightest position where an e.p. move makes a difference? Of course I mean a retrolegal one, otherwise Kh3 Bc1 Pg4 - Kh5 Ph4 Pg6
or suchlike would count.
 
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(2) Posted by Jan Hein Verduin [Thursday, Jan 25, 2018 19:12]

Not sure if this is what you mean, but as an opening bid this one seems unbeatable:

(= 2+2 )

white to move

With e.p. this is a draw, but without it 1.e4 wins.

(I don't have access to the Nalimov dbase and only to Shredder, and that one seems to know about e.p.)
 
 
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(3) Posted by Geir Sune Tallaksen Østmoe [Thursday, Jan 25, 2018 19:20]

Nalimov does support ep. Do you have an example where it doesn’t?
 
   
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(4) Posted by Hauke Reddmann [Friday, Jan 26, 2018 01:20]

But in this example, the double step *happens* and of course
the TB then has the e.p. answer memorized. It was more with
the pawn already on e4. (It would be a nightmare to program
retrolegal e.p.'s...But since those appear only at n>>7,
it's hardly relevant. I just wanted to know min(n).)
 
   
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(5) Posted by Branislav Djurašević [Friday, Jan 26, 2018 09:26]

Lomonosov EGTB does support en passant!!
http://tb7.chessok.com/
 
 
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(6) Posted by Torsten Linß [Friday, Jan 26, 2018 16:29]

@Hauke:retrograde analysis is irrelevant for table bases. Retracting moves you can and will run into illegal positions even without ep captures. Positions in tables bases have a future only, but no past.

For example in the Lomonossow TB you find the following position which is clearly illegal
b7/1p6/8/8/8/K7/8/1k6 w - -
And the TB tells you that it is a mate in 19.
 
   
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(7) Posted by Joost de Heer [Friday, Jan 26, 2018 23:06]

 QUOTE 

Positions in tables bases have a future only, but no past.

But if the past shows that the last move must've been a double step, the future must include the ep capture. And in some cases this will influence the result.
 
   
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(8) Posted by Hauke Reddmann [Friday, Jan 26, 2018 23:49]

Yes, that was exactly what I meant (but I don't think there
is a retrolegal, gamechanging ep with onle 7 men).
 
   
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(9) Posted by Marjan Kovačević [Saturday, Jan 27, 2018 00:59]

To check Nalimov ep you can see if it reports #4 in: 3N4/N7/k1B5/PpK5/8/8/8/8
 
   
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(10) Posted by Torsten Linß [Saturday, Jan 27, 2018 11:56]

@Hauke & Jost: No. With say a white pawn on the fourth rank and black to play there are two positions stored in the TB. One is flagged "ep possible" the other one "ep impossible".
 
   
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(11) Posted by Joost de Heer [Saturday, Jan 27, 2018 12:05]

Castling possible/not possible is not the same as castling legal/not legal.
 
   
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(12) Posted by Geir Sune Tallaksen Østmoe [Saturday, Jan 27, 2018 14:17]

I can’t see a 6- or 7- piece position where it makes a difference in a game/study. This is the best I can do:

(= 5+3 )

 
   
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(13) Posted by seetharaman kalyan [Saturday, Jan 27, 2018 18:39]

This is a smart idea !
 
   
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(14) Posted by Siegfried Hornecker [Friday, Feb 2, 2018 08:48]; edited by Siegfried Hornecker [18-02-02]

EDIT: Oops, this is more about en passant. Still leaving this here as original source for Hauke's position.

(= 3+2 )

A. S. Selezniev, Tidskrift för Schack 1921
White to move and win
 
 
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MatPlus.Net Forum Internet and Computing Nalimov and castling/ep