Does your engine take the poisoned pawn?

[Dr.Ex]

I think the thing that makes it interesting is that a whole bunch of super-strong engines that clearly understand poisoned pawns want to take it anyway (at least for some time period).

I disagree. It takes only a few ply to see that the bishop will be lost.

Maybe you don't have a super strong engine, yet.
My Fritz doesn't spot that at depth 20.

This is exactly what I meant. The point is not whether the bishop is lost. If white wants it, it can get it and that is not some deep line. Therefor having evaluation terms for trapped bishops does not help to avoid the capture on h2 in this position.

The point is to assess what kind of compensation black will have in its pawn structure. Simple programs like CTD do not see much compensation and see that black does not have pieces left with sufficient pawns on the board. And by just counting wood (plus perhaps some bonusses/penalties for last piece captured) it will decline the offered pawn.

Fritz does seem to think that there is compensation in the black pawn structure for the bishop and accepts (as white) a black pawn sac on h4 instead of collecting the bishop.

I think Fritz does initially not see that the bishop will be lost by force.
I think it does not see the line h3 Kg4 Bg1 Kxh3 Bxf2 Bd2 early.
It seems unlikely to me that Fritz (especially Fritz 9, which evaluates the position after h4 Kf3 +1.2 for white) ever thinks there is enough compensation for the bishop.

[Dann Corbit]

I think the thing that makes it interesting is that a whole bunch of super-strong engines that clearly understand poisoned pawns want to take it anyway (at least for some time period).

I disagree. It takes only a few ply to see that the bishop will be lost.

Maybe you don't have a super strong engine, yet.
My Fritz doesn't spot that at depth 20.

This is exactly what I meant. The point is not whether the bishop is lost. If white wants it, it can get it and that is not some deep line. Therefor having evaluation terms for trapped bishops does not help to avoid the capture on h2 in this position.

The point is to assess what kind of compensation black will have in its pawn structure. Simple programs like CTD do not see much compensation and see that black does not have pieces left with sufficient pawns on the board. And by just counting wood (plus perhaps some bonusses/penalties for last piece captured) it will decline the offered pawn.

Fritz does seem to think that there is compensation in the black pawn structure for the bishop and accepts (as white) a black pawn sac on h4 instead of collecting the bishop.

The Baron 2.22 (quite a bit stronger than CTD) does have trapped bishop evaluation and could play Bxh2 in a tournament game as it sticks with it for quite a long time.

So I just disagreed with Dann that it was interesting that super-strong engines would play Bxh2 despite their understanding of poisoned pawns as:
- poisoned pawns evaluation has noting to do with wanting to play Bxh2
- there are good explanations for why they go for it while others seem to refute it pretty quickly.

Richard.

I am not sure if it is a good move or a bad move. It is very obvious that the bishop will be lost. That is what makes it interesting.

[M ANSARI]

I remember checking out this game and I remember that actually taking the pawn was OK because to capture the bishop white will lose some pawns. You end up with a situation where the black better pawn structure creates enough of a dynamic situation where things are drawn. Still ... if a draw was what Fischer was looking for ... this really is not the best move. Maybe Fischer thought he would get good chances to win with his better connected pawn structure, and he probably thought that once these pawns start rolling the bishop will be unable to stop them ... or maybe it was a bluff hoping that Spassky would think Fischer had seen something very deep and might decide not to take the bishop and play a pawn down. As we all know Fischer's move backfired badly.

[Dann Corbit]

I remember checking out this game and I remember that actually taking the pawn was OK because to capture the bishop white will lose some pawns. You end up with a situation where the black better pawn structure creates enough of a dynamic situation where things are drawn. Still ... if a draw was what Fischer was looking for ... this really is not the best move. Maybe Fischer thought he would get good chances to win with his better connected pawn structure, and he probably thought that once these pawns start rolling the bishop will be unable to stop them ... or maybe it was a bluff hoping that Spassky would think Fischer had seen something very deep and might decide not to take the bishop and play a pawn down. As we all know Fischer's move backfired badly.

Wasn't the game drawn in the actual event? I believe that all sensible moves lead to a draw here, and so I think that Fischer lost nothing.

[George Tsavdaris]

Wasn't the game drawn in the actual event? I believe that all sensible moves lead to a draw here, and so I think that Fischer lost nothing.

Actually Fischer lost in this.
It was the first game. He lost the second too without playing for the known reasons. Yet, he won the match anyway finally.....

The game with analysis with the draw line that draws the game, after playing the Bxh2 capture of the poisoned Pawn, that it is not poisoned after all.
It was for Fischer of course.

[Event "?"]
[Site "?"]
[Date "1972.??.??"]
[Round "1"]
[White "Spassky"]
[Black "Fischer"]
[Result "1-0"]
[ECO "E56"]
[PlyCount "111"]
[EventDate "1972.??.??"]

1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Bb4 5. e3 O-O 6. Bd3 c5 7. O-O Nc6 8. a3
Ba5 9. Ne2 dxc4 10. Bxc4 Bb6 11. dxc5 Qxd1 12. Rxd1 Bxc5 13. b4 Be7 14. Bb2 $14
Bd7 $1 15. Rac1 Rfd8 16. Ned4 Nxd4 17. Nxd4 Ba4 18. Bb3 Bxb3 19. Nxb3 Rxd1+ 20.
Rxd1 Rc8 21. Kf1 Kf8 22. Ke2 Ne4 23. Rc1 Rxc1 24. Bxc1 f6 25. Na5 Nd6 26. Kd3
Bd8 27. Nc4 Bc7 28. Nxd6 Bxd6 29. b5 Bxh2 $6 30. g3 h5 31. Ke2 h4 32. Kf3 Ke7
33. Kg2 hxg3 34. fxg3 Bxg3 35. Kxg3 Kd6 36. a4 Kd5 37. Ba3 Ke4 $4 (37... a6 $1
$10 38. b6 (38. bxa6 bxa6 $10 39. Kf3 g5 40. Be7 g4+ 41. Kxg4 Ke4 42. Bxf6 Kxe3
$11) (38. Bf8 axb5 39. axb5 Ke4 40. Bxg7 (40. Kf2 f5 41. Bxg7 e5 42. Ke2 f4 43.
b6 fxe3 44. Bh6 Kd5 45. Bxe3 $11) (40. Bc5 e5 41. Kg4 f5+ $11) 40... Kxe3 41.
Bxf6 b6 $11) (38. Kf4 axb5 39. axb5 b6 40. Bf8 g6 41. Be7 e5+ 42. Kf3 f5 43.
Bf6 Kc4 44. Bxe5 Kxb5 45. Bc7 Kc5 46. Bd8 b5 47. Bf6 (47. Ke2 Kc4 48. Kd2 b4
49. Bf6 b3 50. Bg5 Kb4 $11) 47... Kd5 $11) 38... Kc6 39. a5 (39. Bf8 Kxb6 40.
Bxg7 Ka5 41. Bxf6 Kxa4 42. Kf4 b5 43. Ke5 b4 44. Kxe6 b3 45. Kd5 Kb4 46. e4 a5
$10) 39... Kb5 40. Bf8 Kxa5 $11) 38. Bc5 $1 a6 39. b6 f5 40. Kh4 f4 $2 41. exf4
Kxf4 42. Kh5 $1 Kf5 43. Be3 Ke4 44. Bf2 Kf5 45. Bh4 e5 46. Bg5 e4 47. Be3 Kf6
48. Kg4 Ke5 49. Kg5 Kd5 50. Kf5 a5 51. Bf2 g5 52. Kxg5 Kc4 53. Kf5 Kb4 54. Kxe4
Kxa4 55. Kd5 Kb5 56. Kd6 1-0

[smirobth]

Wasn't the game drawn in the actual event? I believe that all sensible moves lead to a draw here, and so I think that Fischer lost nothing.

Actually Fischer lost in this.
It was the first game. He lost the second too without playing for the known reasons. Yet, he won the match anyway finally.....

The game with analysis with the draw line that draws the game, after playing the Bxh2 capture of the poisoned Pawn, that it is not poisoned after all.
It was for Fischer of course.

[Event "?"]
[Site "?"]
[Date "1972.??.??"]
[Round "1"]
[White "Spassky"]
[Black "Fischer"]
[Result "1-0"]
[ECO "E56"]
[PlyCount "111"]
[EventDate "1972.??.??"]

1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Bb4 5. e3 O-O 6. Bd3 c5 7. O-O Nc6 8. a3
Ba5 9. Ne2 dxc4 10. Bxc4 Bb6 11. dxc5 Qxd1 12. Rxd1 Bxc5 13. b4 Be7 14. Bb2 $14
Bd7 $1 15. Rac1 Rfd8 16. Ned4 Nxd4 17. Nxd4 Ba4 18. Bb3 Bxb3 19. Nxb3 Rxd1+ 20.
Rxd1 Rc8 21. Kf1 Kf8 22. Ke2 Ne4 23. Rc1 Rxc1 24. Bxc1 f6 25. Na5 Nd6 26. Kd3
Bd8 27. Nc4 Bc7 28. Nxd6 Bxd6 29. b5 Bxh2 $6 30. g3 h5 31. Ke2 h4 32. Kf3 Ke7
33. Kg2 hxg3 34. fxg3 Bxg3 35. Kxg3 Kd6 36. a4 Kd5 37. Ba3 Ke4 $4 (37... a6 $1
$10 38. b6 (38. bxa6 bxa6 $10 39. Kf3 g5 40. Be7 g4+ 41. Kxg4 Ke4 42. Bxf6 Kxe3
$11) (38. Bf8 axb5 39. axb5 Ke4 40. Bxg7 (40. Kf2 f5 41. Bxg7 e5 42. Ke2 f4 43.
b6 fxe3 44. Bh6 Kd5 45. Bxe3 $11) (40. Bc5 e5 41. Kg4 f5+ $11) 40... Kxe3 41.
Bxf6 b6 $11) (38. Kf4 axb5 39. axb5 b6 40. Bf8 g6 41. Be7 e5+ 42. Kf3 f5 43.
Bf6 Kc4 44. Bxe5 Kxb5 45. Bc7 Kc5 46. Bd8 b5 47. Bf6 (47. Ke2 Kc4 48. Kd2 b4
49. Bf6 b3 50. Bg5 Kb4 $11) 47... Kd5 $11) 38... Kc6 39. a5 (39. Bf8 Kxb6 40.
Bxg7 Ka5 41. Bxf6 Kxa4 42. Kf4 b5 43. Ke5 b4 44. Kxe6 b3 45. Kd5 Kb4 46. e4 a5
$10) 39... Kb5 40. Bf8 Kxa5 $11) 38. Bc5 $1 a6 39. b6 f5 40. Kh4 f4 $2 41. exf4
Kxf4 42. Kh5 $1 Kf5 43. Be3 Ke4 44. Bf2 Kf5 45. Bh4 e5 46. Bg5 e4 47. Be3 Kf6
48. Kg4 Ke5 49. Kg5 Kd5 50. Kf5 a5 51. Bf2 g5 52. Kxg5 Kc4 53. Kf5 Kb4 54. Kxe4
Kxa4 55. Kd5 Kb5 56. Kd6 1-0

The analysis in the side line you presented after 37...a6 is flawed. 38.b6 Kc6 39.Bf8 Kxb6?? loses after 40.Bxg7 Ka5 41.Bxf6 Kxa4; White has a 6-man tablebase win.

[George Tsavdaris]

Wasn't the game drawn in the actual event? I believe that all sensible moves lead to a draw here, and so I think that Fischer lost nothing.

Actually Fischer lost in this.
It was the first game. He lost the second too without playing for the known reasons. Yet, he won the match anyway finally.....

The game with analysis with the draw line that draws the game, after playing the Bxh2 capture of the poisoned Pawn, that it is not poisoned after all.
It was for Fischer of course.

[Event "?"]
[Site "?"]
[Date "1972.??.??"]
[Round "1"]
[White "Spassky"]
[Black "Fischer"]
[Result "1-0"]
[ECO "E56"]
[PlyCount "111"]
[EventDate "1972.??.??"]

1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Bb4 5. e3 O-O 6. Bd3 c5 7. O-O Nc6 8. a3
Ba5 9. Ne2 dxc4 10. Bxc4 Bb6 11. dxc5 Qxd1 12. Rxd1 Bxc5 13. b4 Be7 14. Bb2 $14
Bd7 $1 15. Rac1 Rfd8 16. Ned4 Nxd4 17. Nxd4 Ba4 18. Bb3 Bxb3 19. Nxb3 Rxd1+ 20.
Rxd1 Rc8 21. Kf1 Kf8 22. Ke2 Ne4 23. Rc1 Rxc1 24. Bxc1 f6 25. Na5 Nd6 26. Kd3
Bd8 27. Nc4 Bc7 28. Nxd6 Bxd6 29. b5 Bxh2 $6 30. g3 h5 31. Ke2 h4 32. Kf3 Ke7
33. Kg2 hxg3 34. fxg3 Bxg3 35. Kxg3 Kd6 36. a4 Kd5 37. Ba3 Ke4 $4 (37... a6 $1
$10 38. b6 (38. bxa6 bxa6 $10 39. Kf3 g5 40. Be7 g4+ 41. Kxg4 Ke4 42. Bxf6 Kxe3
$11) (38. Bf8 axb5 39. axb5 Ke4 40. Bxg7 (40. Kf2 f5 41. Bxg7 e5 42. Ke2 f4 43.
b6 fxe3 44. Bh6 Kd5 45. Bxe3 $11) (40. Bc5 e5 41. Kg4 f5+ $11) 40... Kxe3 41.
Bxf6 b6 $11) (38. Kf4 axb5 39. axb5 b6 40. Bf8 g6 41. Be7 e5+ 42. Kf3 f5 43.
Bf6 Kc4 44. Bxe5 Kxb5 45. Bc7 Kc5 46. Bd8 b5 47. Bf6 (47. Ke2 Kc4 48. Kd2 b4
49. Bf6 b3 50. Bg5 Kb4 $11) 47... Kd5 $11) 38... Kc6 39. a5 (39. Bf8 Kxb6 40.
Bxg7 Ka5 41. Bxf6 Kxa4 42. Kf4 b5 43. Ke5 b4 44. Kxe6 b3 45. Kd5 Kb4 46. e4 a5
$10) 39... Kb5 40. Bf8 Kxa5 $11) 38. Bc5 $1 a6 39. b6 f5 40. Kh4 f4 $2 41. exf4
Kxf4 42. Kh5 $1 Kf5 43. Be3 Ke4 44. Bf2 Kf5 45. Bh4 e5 46. Bg5 e4 47. Be3 Kf6
48. Kg4 Ke5 49. Kg5 Kd5 50. Kf5 a5 51. Bf2 g5 52. Kxg5 Kc4 53. Kf5 Kb4 54. Kxe4
Kxa4 55. Kd5 Kb5 56. Kd6 1-0

The analysis in the side line you presented after 37...a6 is flawed. 38.b6 Kc6 39.Bf8 Kxb6?? loses after 40.Bxg7 Ka5 41.Bxf6 Kxa4; White has a 6-man tablebase win.

Really? I see 7 pieces.
And a draw.....
Do you have a refutation in the line i give?

[d]8/1p6/p3pB2/8/k7/4P1K1/8/8 w - - 0 42

[smirobth]

Wasn't the game drawn in the actual event? I believe that all sensible moves lead to a draw here, and so I think that Fischer lost nothing.

Actually Fischer lost in this.
It was the first game. He lost the second too without playing for the known reasons. Yet, he won the match anyway finally.....

The game with analysis with the draw line that draws the game, after playing the Bxh2 capture of the poisoned Pawn, that it is not poisoned after all.
It was for Fischer of course.

[Event "?"]
[Site "?"]
[Date "1972.??.??"]
[Round "1"]
[White "Spassky"]
[Black "Fischer"]
[Result "1-0"]
[ECO "E56"]
[PlyCount "111"]
[EventDate "1972.??.??"]

1. d4 Nf6 2. c4 e6 3. Nf3 d5 4. Nc3 Bb4 5. e3 O-O 6. Bd3 c5 7. O-O Nc6 8. a3
Ba5 9. Ne2 dxc4 10. Bxc4 Bb6 11. dxc5 Qxd1 12. Rxd1 Bxc5 13. b4 Be7 14. Bb2 $14
Bd7 $1 15. Rac1 Rfd8 16. Ned4 Nxd4 17. Nxd4 Ba4 18. Bb3 Bxb3 19. Nxb3 Rxd1+ 20.
Rxd1 Rc8 21. Kf1 Kf8 22. Ke2 Ne4 23. Rc1 Rxc1 24. Bxc1 f6 25. Na5 Nd6 26. Kd3
Bd8 27. Nc4 Bc7 28. Nxd6 Bxd6 29. b5 Bxh2 $6 30. g3 h5 31. Ke2 h4 32. Kf3 Ke7
33. Kg2 hxg3 34. fxg3 Bxg3 35. Kxg3 Kd6 36. a4 Kd5 37. Ba3 Ke4 $4 (37... a6 $1
$10 38. b6 (38. bxa6 bxa6 $10 39. Kf3 g5 40. Be7 g4+ 41. Kxg4 Ke4 42. Bxf6 Kxe3
$11) (38. Bf8 axb5 39. axb5 Ke4 40. Bxg7 (40. Kf2 f5 41. Bxg7 e5 42. Ke2 f4 43.
b6 fxe3 44. Bh6 Kd5 45. Bxe3 $11) (40. Bc5 e5 41. Kg4 f5+ $11) 40... Kxe3 41.
Bxf6 b6 $11) (38. Kf4 axb5 39. axb5 b6 40. Bf8 g6 41. Be7 e5+ 42. Kf3 f5 43.
Bf6 Kc4 44. Bxe5 Kxb5 45. Bc7 Kc5 46. Bd8 b5 47. Bf6 (47. Ke2 Kc4 48. Kd2 b4
49. Bf6 b3 50. Bg5 Kb4 $11) 47... Kd5 $11) 38... Kc6 39. a5 (39. Bf8 Kxb6 40.
Bxg7 Ka5 41. Bxf6 Kxa4 42. Kf4 b5 43. Ke5 b4 44. Kxe6 b3 45. Kd5 Kb4 46. e4 a5
$10) 39... Kb5 40. Bf8 Kxa5 $11) 38. Bc5 $1 a6 39. b6 f5 40. Kh4 f4 $2 41. exf4
Kxf4 42. Kh5 $1 Kf5 43. Be3 Ke4 44. Bf2 Kf5 45. Bh4 e5 46. Bg5 e4 47. Be3 Kf6
48. Kg4 Ke5 49. Kg5 Kd5 50. Kf5 a5 51. Bf2 g5 52. Kxg5 Kc4 53. Kf5 Kb4 54. Kxe4
Kxa4 55. Kd5 Kb5 56. Kd6 1-0

The analysis in the side line you presented after 37...a6 is flawed. 38.b6 Kc6 39.Bf8 Kxb6?? loses after 40.Bxg7 Ka5 41.Bxf6 Kxa4; White has a 6-man tablebase win.

Really? I see 7 pieces.
And a draw.....
Do you have a refutation in the line i give?

[d]8/1p6/p3pB2/8/k7/4P1K1/8/8 w - - 0 42

I misspoke. Yes, it is 7 pieces ... but it will soon be 6 since the Black e-pawn cannot be defended. The line you gave (42.Kf4 b5 43.Ke5 b4 44.Kxe6) reaches this position:

[d]8/8/p3KB2/8/kp6/4P3/8/8 b - - 0 44

which a tablebase win for White. After the further moves:
44...b3 45.Kd5 Kb4 46.e4?? is a draw, but 46.Bb2! wins. Play might continue 46...a5 47.Kd4! a4 48.Kd3! a3 49.Bg7

[George Tsavdaris]

I misspoke. Yes, it is 7 pieces ... but it will soon be 6 since the Black e-pawn cannot be defended. The line you gave (42.Kf4 b5 43.Ke5 b4 44.Kxe6) reaches this position:

[d]8/8/p3KB2/8/kp6/4P3/8/8 b - - 0 44

which a tablebase win for White. After the further moves:
44...b3 45.Kd5 Kb4 46.e4?? is a draw, but 46.Bb2! wins. Play might continue 46...a5 47.Kd4! a4 48.Kd3! a3 49.Bg7

Yes you are right, it's one of the rare times where Shredder 10 with Shredderbases fail to see the move. I should have used for the analysis the 6 piece tablebases but i wanted to avoid the loading time.
So now we have to find a better defense for black....

[smirobth]

Yes you are right, it's one of the rare times where Shredder 10 with Shredderbases fail to see the move. I should have used for the analysis the 6 piece tablebases but i wanted to avoid the loading time.
So now we have to find a better defense for black....

I don't think there is a defense for Black after 37...a6 38.b6
The line you gave, including the error, was also given by Kasparov in My Great Predecessors Part IV (Kasparov attributes the line to Purdy, Chessbase's Megabase also has this line, plus I believe Timman also repeats Purdy's line in his "Fischer World Champion!" book, although I don't have that book to be certain) .... so you are in good company.

Most analysis I have seen seems to indicate that 39...f5? was a losing move and that 39...e5! could have held the draw. For this reason it has been suggested that Spassky's 36.a4 was a mistake and that he should have first played 36.Kg4 to force 36...g6 and only then play 37.a4.

I may go over the analysis in My Great Predecessors in more detail when I get some time. This is a very hard ending to analyze and there have been many mistakes in published analysis over the years, but with the advent of the KBP vs KPP tablebase it may now be humanly possible to find the truth.