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Old July 21st 17, 10:23 PM posted to rec.games.chess.computer,rec.games.chess.analysis
Rainer[_2_]
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Posts: 30
Default Engine puzzle position

On 21/07/2017 17:14, Martin Brown wrote:

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 : [...]


You didn't post the game, so I have to ask: is there a position
repetition after 21...Bc8? If so, a zero score would be acceptable.

Cheers,
Rainer