Author: James T. Walker
Date: 05:59:07 03/29/99
Go up one level in this thread
On March 29, 1999 at 03:56:08, blass uri wrote: > >On March 28, 1999 at 23:08:45, blass uri wrote: > >> >>On March 28, 1999 at 22:54:53, blass uri wrote: >> >> <snip,snip> I found that the tablebases assume >>that every promotion not to a queen is a draw in KRP vs KR and I did not succeed >>to compose a problem when the only way to win with KRP vs KR is an >>underpromotion. >> >>Uri > >I found a position when Junior (using tablebases) goes wrong in the winning side >of KRP vs KR > >6R1/7k/5P2/8/8/8/7r/K7 w - - 0 1 > >Fritz's tablebases show the right winning move 1.f7 (8) (I do not understand the >8) but after this move the tablebases show for black Rf2 with draw. > *************** Yes, this is an error in the tablebase because is has the next move as f8=B which is a draw. I believe f8=N is a draw also. In both cases black plays KxR and it ends up with KN vs KR or KB vs KR both draws. Again, the (8) is the number of moves to "Conversion". The (8) 1. f7 is correct and leads to conversion in 8 moves with best play. That means that in (8) moves white will either queen the pawn or black will have to exchange its rook for the other rook or for the pawn or for whatever piece the pawn is promoted to (Another rook). At that point white has a "Won" endgame and abandons the CD ROM because it believes the program can win the game from there. These tablebases are to "Conversion" and not to "Mate" as in Crafty's case. An example of the (8) moves to conversion might be 1....Rh1+ 2. Kb2 Rh2+ 3. Kc3 Rh3+ 4.Kd4 Rh4+ 5. Ke5 Rh5+ 6.Kf6 Rh6+ 7.Ke7 R to anywhere 8.f8=R . Now we have "Conversion" . Two rooks vs one rook is a win and the end of the tablebases. There are other lines leading to "Conversion" in 8 moves. Of course if you do not make the "Best" move you may lead to conversion in 3. Example 1....Rf2 2. f8=R RxR 3. RxR and white has "Converted" to a won endgame and no more CD ROM. ******** >After 1...Rf2 tablebases show 2.f8B as the first move instead of 2.f8R with an >easy win for white. ********* Yes, this is an error in the tablebase. ********* >I am not sure about the result of 2.f8Q, the only question is if black has a >perpetual check and I did not analyze this position and did not check it with >KQR vs KR tablebases. > ********** Yes, I believe the 2. f8=Q is a draw because of moves like Ra2+. Jim Walker *************** >Uri
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