Author: John Lowe
Date: 09:28:18 12/29/02
Go up one level in this thread
On December 29, 2002 at 11:29:49, Uri Blass wrote: >On December 29, 2002 at 10:16:33, Dan Andersson wrote: > >>There are a number of way to check if a pawn position is pseudo-legal. >>Backtracking is fairly cheap. And if you want to bound it by the number of >>captures made it is easy. Add a cost array and you are done. A quicker test is >>using this property: >> The 'backwards capture triangle' area of any pawn must not have more pawns in >>it than the number of squares at its base. This can also be bounded by the >>available number of captures. >> P >> xxx >> xxxxx >> bbbbbbb >> >>MvH Dan Andersson > >I did not think a lot about the problem but >you need first a clear definition to decide if a pawn structure is legal > >It is easy to detect part of the illegal structures but proving that all the >other structures are possible is not a trivial task. > >Here is an example that is not trivial > > >Is the following pawn structure legal? > >[D]4k3/8/P7/PPPPPPP1/1ppppppp/7p/8/4K3 w - - 0 1 > >After one minute of looking at the position I coould not convince myself that it >has to be legal but also could not find a proof that it is illegal. > >It is clear that if you add a piece it is illegal. > >Uri Go on Uri! If you can achieve that position in a legal game it will go down in hisory as Uri's zipper ;)
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