Author: Robert Hyatt
Date: 06:32:22 02/27/00
Go up one level in this thread
On February 27, 2000 at 00:15:14, Richard A. Fowell (fowell@netcom.com) wrote: >I noticed today that six of the seven chess programs that I tried >(three freeware, four commercial) failed to pass the two tests below. > >(my congratulations to Will Bryant, who programmed Screamer right!) > >The others don't understand how castling rights and en passant capture >rights effect the ability to claim draw by three-fold repetition of position. > >The FIDE Laws of Chess (1997, but unchanged from when I learned chess 26 years >ago) say: > >================================================================= >9.2. The game is drawn, upon a correct claim by the player having the move, when >the same position, for at least the third time (not necessarily by repetition of >moves) > > (a) is about to appear, if he first writes his move on his scoresheet and >declares to the arbiter his intention to make this move, or > > (b) has just appeared. > > Positions as in (a) and (b) are considered the same, if the same player >has the move, pieces of the same kind and colour occupy the same squares, and > the possible moves of all the pieces of both players are the same. >Positions are not the same if a pawn could have been captured en passant or if >theright to castle immediately or in the future has been changed. >================================================================== > >The part programmers seem to have difficulty with is that last sentence. > >This citation is from the Malta Chess Federation site: >http://www.kemmunet.net.mt/chessmalta/fidelaws/ > >Try these two games out on your program. >A draw cannot be claimed in either sequence, due to that last >sentence (and, again - it isn't new). > >#1 Check for knowledge of castling rights on triple repetition draw = > >1. Nf3 Nf6 >2. Rg1 Rg8 >3. Rh1 Rh8 (second occurrence of this visible piece pattern, but first >occurrence w/o castling rights) >4. Rg1 Rg8 >5. Rh1 Rh8 ( No draw, yet - this is the original piece pattern, but there > both sides had castling rights. To put it another way, the EPD > strings for the starting position and this one are different.) >6. Rg1 Rg8 - draw by triple repetition of position. > >#2 Check for knowledge of en passant opportunity of triple repetition draw = > >1. a4 a6 >2. a5 b4 >3. Nf3 Nf6 >4. Ng1 Ng8 (second occurrence of this visible piece pattern, but first >occurrence w/o en passant capture option) >5. Nf3 Nf6 >6. Ng1 Ng8 (again, no draw yet - there is no en passant capture possible here, > as there was after Black's second move). >7. Nf3 - draw by triple repetition of position. > >------------- >This can be done properly, by keeping track of the >castling rights and en passant situation. > >Which chess programs (other than Screamer) get these right? > >Richard A. Fowell (fowell@netcom.com) >http://dmoz.org/Games/Board_Games/Chess/Software/Macintosh/ > >P.S.: Of course, programs (or humans) don't HAVE to claim the draw. > But, for programs that do, they can't claim it > >P.P.S: Screamer is a freeware Macintosh program at: > http://pweb.netcom.com/~wbryant/screamer.html Crafty has always done this correctly... castling status/EP status is encoded into the hash signature, which is used for repetition detection...
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