6

I found myself in this position as Black. I played Kb6, but the engine on chess.com suggested that the move Kb7 is a missed win, and the continuation below would have been winning for me. It gave no lines beyond what is below, and I can't see how this is a win for Black. Is this a fault with the engine, or is there some line that I've completely missed?

[Title "Unexplained"]
[FEN "2b2r2/2p5/p1kb2qp/1p1p4/3P4/7P/PP1BQPP1/RNR3K1 b - - 0 1"]

1...Kb7 2.Qe3 Rg8

In response to comments questioning if I have the position wrong or missed a root, I confirm I was a full rook down and felt this was a completely lost position. I have now included a screenshot demonstrating the strange opinion of the engine at chess.com

I guess it's a bug with the engine then?

enter image description here

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  • 3
    Double check the position, and make sure that you did not leave out a black rook. If not, as Phonon said, you are just lost. – PhishMaster Oct 11 '19 at 12:04
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    And this is why you should not rely on engines for game analysis – David Oct 11 '19 at 12:55
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    @David I certainly wouldn't in the first instance, but after doing my own analysis on certain games I found interesting, it's usually worth using computer analysis to see if there were any big moves that were missed – Darren H Oct 11 '19 at 13:17
  • Hi, this post seems to have received decent answers, if you have found one to be particularly satisfactory please consider accepting it, as it's important to give closure to well addressed posts. Thanks for considering it. – user929304 Oct 12 '19 at 11:38
8

This is not a missed win for black, both Kb6 and Kb7 are equally losing for black as you are simply a full rook down without any real compensation. Qe3 move simply stops black's only way to breakthrough as it stops Bxh3. That is not white's only move either, Kh1 and Rc3 (though walks in the way of the knight) are sufficiently good for white too.

So either:

  • The cloud engine didn't get to run sufficiently long and gave a wrong evaluation, or

  • you simply mis-read or mis-interpreted the evaluation of the engine, or

  • you're showing us the wrong position here.

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  • Thanks for your answer. I have updated my question which points to your first suggestion. I've since changed the settings from '10 seconds' to 'Unlimited' and increased lines to the maximum (5) from 3, and it still gives the same suggestion. Is there a way I can report this to chess.com as a bug then? – Darren H Oct 11 '19 at 12:43
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    @DarrenH Yeah both the textual and numerical evals are wrong, because probably the algorithm uses a very short ponder time for the engine to evaluate when parsing the whole game and in the Kb7 line as you see its evaluation stems from a depth 1 calculation, hence it's completely unreliable. You can report these things of course, try bottom left of your screen there's a help icon, once you click a "report bug" option should appear. For analysing your games with an engine, it's much simpler to just copy your game or its FEN to lichess (among others) and analyse there, all features are free. – Ellie Oct 11 '19 at 12:53
  • Black may have a slim chance for counterplay if White does not play precisely – David Oct 11 '19 at 12:56
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    So the takeaway here then is to use Lichess rather than Chess.com. Do they use different software? Why is Lichess better? – Darren H Oct 11 '19 at 13:18
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    @DarrenH no! the takeaway here should be that both Kb6 and Kb7 are losing since that's what your question was. Now whether you wanna use lichess.org or chess.com is entirely up to you, I just gave you a practical recommendation. – Ellie Oct 11 '19 at 14:30
3

Yes, it is a bug. I just plugged that updated position into Stockfish 10 running on a quad-core 2.9 GHz laptop, and it is still over +5.

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    Still have not had time, but I will. We have had company coming this week for 10 days, and I am in the middle of a major email migration for a customer. – PhishMaster Oct 11 '19 at 12:45

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