Author: Bob Durrett
Date: 20:30:21 11/16/02
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On November 16, 2002 at 22:08:55, Christophe Theron wrote: <snip> >Don't you need to prove first that two different chess positions will always >have a different legal moves list? And that there exist no move list that could >be associated with two different chess positions? > > > > Christophe I feel like I am talking to myself in this thread, except for the above. Well, I now see that it is possible to have more than one position with the same legal move list. This would occur if a piece were to be on the board but with no legal moves available for it. Another position, with that piece absent, would have the same legal move list. Whether or not both positions might be legal is something still unclear. If there were a queen on the board with no legal moves, then it might be replaced by another piece. A "smothered queen" might be an example. In fact, any "smothered" piece might be replaced by another piece or by no piece at all, as long as the new piece was also "smothered." _ _ _ _ _ _ _ _ _ The consequence of this is that positions cannot be represented uniquely by a legal move listing by itself. Each position could, however, be represented by the combination of a legal move list PLUS an identification of all pieces, and their locations, for which there is no legal move. _ _ _ _ _ _ _ _ _ Notice that this is all irrelevant, in the scenario I described, since there would still be only one of the possible positions for each "move listing" produced by the process described. Bob D.
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