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Old July 21st 17, 04:14 PM posted to rec.games.chess.computer,rec.games.chess.analysis
Martin Brown[_2_]
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Posts: 2
Default Engine puzzle position

I have stumbled upon a position where quite a few engines - I thought at
first it was just x64 types but Fritz 10 also sees the same phantom
"Good move" which evaluates as a draw where none exists. The position is
hopelessly lost but that isn't the point. Something is wrong.

I found it analysing a lost game where there was a clear and bizarre
discontinuity in the evaluation function that made no sense to me.

Crafty x64 23.05 also sees the wrong right move but x32 20.14 is OK.

r2r4/1p2p1kp/p5p1/3BNbPn/8/2N4P/PPP2P2/R3K2R b KQ - 0 21

It is a close run thing between 22. ... Rac8, or 22 ... Nf4
but the phantom move which evaluates as a draw is 22. ... Bc8

If you actually play this move Bc8 then the evaluation becomes correct
again with white to move. There is something odd about this position
that breaks some engines. Any ideas what it might be?

My guess is that it is some sort of draw by repetition bug common to
several of the engines since the offending thread displays as just a
single move with no continuation line :

354: Deep Fritz 14 - M, Blitz 5m+5s-4m+2s
r2r4/1p2p1kp/p5p1/3BNbPn/8/2N4P/PPP2P2/R3K2R b KQ - 0 1

Analysis by Deep Fritz 14 x64:

1. = (0.00): 21...Bc8
2. +- (4.91): 21...Nf4 22.0-0-0 Nxh3 23.Rdf1 Rac8 24.Bxb7 Rc5 25.f4 Rd4
26.Re1 e6 27.Nd3 Rxd3 28.cxd3 Nxf4 29.Bxa6 Bxd3 30.Rh4 Ng2 31.Rxe6 Bxa6
32.Re7+ Kg8 33.Rhxh7 Rxg5 34.Reg7+ Kf8 35.Rf7+ Kg8 36.Rhg7+ Kh8 37.Ne4
3. +- (4.92): 21...Bxc2 22.Bxb7 Rab8 23.Nc6 Rxb7 24.Nxd8 Rxb2 25.Ne6+
Kf7 26.Nc5 Nf4 27.a4 Bf5 28.Ra2
4. +- (4.92): 21...Rac8 22.0-0-0 Nf4 23.Bf3 Rxd1+ 24.Rxd1 Rc5 25.Re1
Nxh3 26.Bxb7 Nxg5 27.Bxa6 h5 28.Bd3 Nf7 29.Nxf7 Kxf7 30.Kd2 Bxd3 31.Kxd3
Rf5 32.a4 h4 33.Ne4 Rd5+ 34.Ke3 Ra5 35.Rh1 Rxa4 36.Rxh4
5. +- (5.18): 21...Rab8 22.0-0-0 Nf4 23.h4 Rbc8 24.Bf3 b5 25.Rxd8 Rxd8
26.Nc6 Re8 27.Rd1 Nh3 28.Rd2
6. +- (5.34): 21...Ra7 22.0-0-0 Nf4 23.h4 Rc8
7. +- (5.37): 21...e6 22.Bxb7 Rab8 23.Nc6 Rxb7 24.Nxd8 Rxb2
8. +- (5.60): 21...Rf8 22.0-0-0 Ra7 23.Rd4 Bc8 24.Re1 b5 25.Nd3 Bxh3
26.Rde4 e6 27.Bxe6 Bg2 28.Rd4 Re7 29.Rd7 Rxd7 30.Bxd7 Ba8 31.Re6 Bb7
32.Rb6 Rb8 33.Nd5

(, 21.07.2017)

And after playing the supposedly drawing move it is obviously junk:

354: Deep Fritz 14 - M, Blitz 5m+5s-4m+2s
r1br4/1p2p1kp/p5p1/3BN1Pn/8/2N4P/PPP2P2/R3K2R w KQ - 0 1

Analysis by Deep Fritz 14 x64:

1. +- (5.69): 22.0-0-0 Ra7 23.h4 Nf4 24.Bb3 Re8 25.Rd4 Nh3 26.f4 Nf2
27.Rg1 Bf5 28.Rg2 Nh3 29.Rgd2 b5 30.Nd5 Rf8 31.Nc6 Rd7 32.Ndxe7
2. +- (5.59): 22.h4 Re8 23.0-0-0 Nf4 24.Rhe1 Rb8 25.Be4 Rf8 26.Nd7
3. +- (5.34): 22.a4 Ra7 23.0-0-0 Rf8 24.Rhe1 Bxh3 25.Nd7 Re8 26.Nf6
Nxf6 27.gxf6+ Kxf6
4. +- (5.20): 22.Nc4 Nf4 23.0-0-0 Rb8 24.Rhe1 e6 25.Bf3 Rxd1+ 26.Rxd1
Nxh3 27.Ne4 b5 28.Ne5 b4 29.Rd8 Rb5 30.Ng4 Bb7 31.Rd7+ Kh8 32.Ngf6 Bxe4
33.Rxh7#
5. +- (5.17): 22.Nd3 Rf8 23.0-0-0 Ra7 24.Rhe1 b5 25.Be6 Bxe6 26.Rxe6
Nf4 27.Nxf4 Rxf4 28.Rde1 Kf8 29.Ne4 a5 30.Rb6 Rf5 31.Rc6 Rd7 32.Nc5 Rdd5
33.Rc8+ Kf7
6. +- (5.09): 22.a3 Ra7 23.0-0-0 Rf8 24.Rhe1 b5 25.h4 Rc7 26.Bf3 Nf4
27.Kb1 Bf5 28.Be4 Bxe4 29.Rxe4 e6 30.Red4 Nd5 31.Ne4
7. +- (5.03): 22.b3 Rf8 23.0-0-0 Ra7 24.Nd3 Nf4 25.Nxf4 Rxf4 26.f3 Rh4
27.Rde1 b5 28.Be6 Bb7 29.Ne4 Ra8 30.Kb2 Rd8 31.Rhg1 b4
8. +- (4.96): 22.Rh2 Nf4 23.0-0-0 a5 24.Rd4 Nxh3 25.Rh4 Nxg5 26.f4 Nh3
27.Bg2 g5 28.R4xh3 Bxh3 29.Rxh3 gxf4 30.Bxb7 Rab8 31.Be4 h6 32.Nc6

(, 21.07.2017)

Some engines can see as far as 0-0-0 from the ply before but the ones
that fail still seem convinced it is a draw with no analysis given.

I'm running under Deep fritz 14 user interface but most of the engines I
have tried so far fail on this position. Crafty x32 a notable exception.

Can anyone shed any light on what is going on?

Is there anyone still reading these groups? - it's awfully quiet...

--
Regards,
Martin Brown