[Retros] Example 4 (better version of E.P.) Yefim 08/23/2004

andrew buchanan andrew at anselan.com
Mon Aug 23 02:38:29 EDT 2004

> i think emerging position after the e.p. must be legal. andrew (from anselan) thinks so as well.

Uh? I didn't say that. The position after the capture would not be legal, because White would be in check.

Art 9.2: "Positions are not the same if a pawn that could have been captured en passant can no longer be captured."

I think that is pretty unambiguous. And if an e.p. is illegal because it would leave/put the player in check, then the pawn can't be captured by e.p. So the positions are the same.

FEN is a bit of a red herring, suggesting a third interpretation. Under this one, the position after 1.e4 is different from the same arrangement of pieces after 2.Na3 Na6 3.Nb1 Nb8. Obviously FEN is an efficient way to encode positions, but has little to do with the argument here.

So I think the e.p. situation is unambiguous. But as I tried to show in my earlier mail, the castling situation is much cloudier.


TregerYefim at aol.com wrote:
From Yefim T about Example 3 or (better version 4, below).
Did everybody agree with Andrey Jakobchich's opinion that in my E.P. example (3-example) positions are different (especially concerning repetition topic)?
I looked at chess rules FIDE. Really, there is rule 3.7d
"A pawn attacking a square crossed by an opponent's pawn which has advanced two squares in one move from its original square may capture this opponent's pawn as though the latter had been moved only one square. This capture may only be made on the move following this advance and is called an 'en passant' capture." confirming that opinion but there is rule 3.9:
"No piece can be moved that will expose its own king to check or leave its own king in check."
So, there is some vulnerability about this, I think emerging position after E.P. must be legal (Andrew "from anselan" thinks as well…)
I am giving even better version, example 4 (picture if any)
White: Ka5 Rb1 p.d5 Black: Kf8, Qg5, Bd8, p.c5 Black's move.
Game follows: 1…c5+! 2. Rb6 Be7 3. Rb1 Bd8+ 4.Rb6 Be7 5.Rb1 Bd8+
Draw? (No need Black Queen g5!)
My point is: as a mathematician I am looking for right and good definition of Position. I think math definition is different from "chess rules definition (if any)".

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