Author: Ricardo Gibert
Date: 19:00:55 07/07/03
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On July 07, 2003 at 19:40:47, Pierre Chevalier wrote: >There are only 480 positions in Shuffle Chess also known as FischerRandom. >The other half of the supposed 960 positions are mirror image errors. >It is standardly accepted that the king moves two squares to castle. >All shuffle chess positions can be represented with the king on c1, e1 or g1. >All other arrangements are left-right reversals. >When the king begins on c1 it castles to g1 or stays put. >When the king begins on e1 as normal it castles to c1 or g1. >When the king begins on g1 it castles to c1 or stays put. >In all these cases the rook will wrap around the king as standard. >The number 960 is the wrong number. To say there are 960 positions is to >count mirror images as if they represented new positions. Mirror image >arrangements do not represent a new format; they represent a mistake in >counting. In this case mirror image means reversing the order along the back >rank. >Consider the position RNBKQBNR. Is this a new position? No. >This is not a new position. >The variant shuffle chess creates 479 new positions in addition to the >standard chess position. I don't think shuffle chess and Fischer Random are the same. In Fischer Random, the "mirror image" positions are significantly different, because in castling K-side the K always goes to g-file and R goes to the f-file, while in castling Q-side the K always goes to c-file and R goes to d-file. The intent of Fischer Random is to have multiple starting positions, but to otherwise keep the game as normal as possible. This explains the reason for the castling rules being what they are and also why one sides Bs must be on opposite color squares and why the K must start somewhere between the Rs.
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