Author: Pierre Chevalier
Date: 16:40:47 07/07/03
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.
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