Author: Robert Hyatt
Date: 20:34:58 05/18/01
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On May 18, 2001 at 18:03:59, J. Wesley Cleveland wrote: > >however, these positions are legal. >[D]rnbqkbRr/p1p1pp1p/1p1p2p1/8/1PPP1PP1/P3P3/8/RNB1KBN1 w Qkq - 0 1 >[D]8/8/8/8/3k4/2p1p3/2P1P3/3bK3 w - - 0 1 Promotions simply add another dimension of difficulty... As I said a couple of times, this is a hard problem. > >Right. I should have said "First, eliminate all obviously illegal positions". I >think you could catch nearly all of them with six cases: >1. illegal combination of material, e.g. 5 queens and 5 pawns. >2. illegal pawn structure, e.g. 6 white pawns on the a file, and black has more >than a king. >3. bishop blocked by 2 pawns on 2nd or 3 pawns on 7th rank, either original or >current position. >4. rook on other side of pawn wall, pawns on all files, none advanced more than >one square and side with rook has all its pawns. >5. king behind opposing pawn wall, with no possible path without being in check >(this seems the most difficult). >6. both kings in check. > >A first try would be to check for 1,2,3 and 6 and put all positions with pawns >on all files, none advanced more than one square, and all positions where there >are no paths from the kings' current positions to their inital positions that >are not attacked by enemy pawns into "not sure". > >Another test might to be to "unmove" each piece to its initial position, >"unmoving" opposing pieces only as necessary.
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