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Clay Polk vs Mariano Sana
TN Open (2016), Nashville, TN USA, rd 5, Sep-04
Queen's Gambit Declined: Exchange. Positional Variation (D35)  ·  0-1



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Kibitzer's Corner
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Jun-12-19  Cibator: White feasts on pawn salad but ends up as Polk salad.
Jun-11-20  Cheapo by the Dozen: I was even sloppier in my analysis than the game's actual player. :) E.g., I thought that 28 ... Rxd4 would be effective because it overloaded White's queen, quite overlooking that the aforementioned queen can just capture the rook WITH CHECK.

And my line after 29 Nxc6 wasn't accurate either ...

Premium Chessgames Member
  al wazir: I think white gets a decent game after 22. bxa7:

22...dxe3 23. Qxe3 Qxe3+ 24. Nxe3 Nxf4 25. Ne2 Nxe2+ 26. Rxe2 Ba8 27. c2 Rxa7 28. Rc8+ Kg7 29. a3.

And 27. Rxb7 certainly looks better than 27. Na5, the move played.

Jun-11-20  jith1207: That's wonderful, <Fusilli>.
Jun-11-20  Muttley101: 27. R:b7 seems to the point.
Jun-11-20  Brenin: Thanks, <Fusilli>: it's great to have such well-informed kibitzing! I spotted that 27 ... Rxd4 28 Qxd4 was check, and nearly gave up before realising that 27 ... Nh3+ had unexpected merits, e.g. 28 Kh1 Rf6, or 28 Kf1 Qa6+ (Qe4 is much better, but I didn't see that). White could have avoided the swindle with 27 Rxb7 Qxb7 28 Qxf4, or 27 Nc5.
Premium Chessgames Member
  agb2002: Black has a bishop for a knight and three pawns.

White threatens Nxc6, Nxb7, Qxf4 and Rxb7.

Black can attack the white king with four pieces, starting with 27... Nh3+:

A) 28.gxh3 Qh1+ 29.Kf2 Rf6+

A.1) 30.Ke3 Qe4(f3)#.

A.2) 30.Ke2 Qf1+ (or 30... Qf3+ 31.Ke1 Qf1#) 31.Ke3 Q(R)f3#.

A.3) 30.Kg3 Qf3+ 31.Kh4 Rf4+ and mate next.

A.4) 30.Qf4 Rxf4+ and mate soon.

B) 28.Kh1 Rf6

B.1) 29.Ne3 Qe4 (threatens Qb1+ and Qxe3)

B.1.a) 30.Qc(e)1 Qxe3 31.Qxe3 (due to Qxc1+ and Bxg2+; 31.Qd1 Qd2 wins) 31... Rf1+ 32.Qg1 Rxg1#.

B.1.b) 30.Nac4 Qb1+ and mate in two.

B.2) 29.Qe2 Qxg2+ 30.Qxg2 Rf1#.

C) 28.Kf1 Qe4 (neither Rf6+ nor Ba6+ seem to work)

C.1) 29.Rxb7 Rf6+

C.1.a) 30.Nf2 Qb1+ 31.Ke2 (31.Qe1 Rxf2+ 32.Kg1 Qxe1#) 31... Rxf2+ 32.Ke3 Rxd2 33.Kxd2 Nf4 looks winning (34.a8=Q Qd3+ and mate next; 34.Rb3 Qe4; 34.Kc3 Qe1+ and 35... Qxa5; 34.Ke3 g5 threatening Qe1+ and creating a mating net).

C.1.b) 30.Qf2 Qd3+ 31.Ke1 Nxf2 32.Nxf2 Qe3+ and mate soon.

C.2) 29.gxh3 Rf6+

C.2.a) 30.Nf2 Qg2+ 31.Ke1 Qg1+ 32.Ke2 Rxf2+ 33.Ke3 Rxd2 34.Kxd2 Qxd4+ and 35... Qxa7 wins decisive material.

C.2.b) 30.Qf2 Qd3+ 31.Ke1 Re6+ 32.Ne3 Rxe3+ 33.Qxe3 Qxe3+ 34.Kd1 (34.Kf1 Bf3 and mate soon) 34... Qxd4+ as above.

C.2.c) 30.Kg1 Qh1#.

Premium Chessgames Member
  Predrag3141: 27 … Nh3+ looked like the only move that doesn't lose. I expected 28 Kf1, but if 28 Kh1 Rf6 29 Ne3 Qb5, hoping it would draw (it does). 29 … Qe4 is a cute win, attacking a hidden weakness on b1.

As for 28 Kf1, it's not a clear win for Black. Stockfish evaluates it as -1.32: 28 … Qe4 29 Qe3 Qxg2+ 30 Ke1 Nf4 31 Nc3 Re6 32 Qxe6 Qg1+ 33.Kd2 Nxe6 34.Rxb7

Jun-11-20  Brenin: <Predrag3141>: In your line after 28 Kf1, isn't 30 ... Ng5, with threats of Nf3+ in addition to Re6, stronger than 30 ... Nf4? Black seems to be winning, or am I missing something?
Jun-11-20  mel gibson: The first move screamed to be played
as White was in so much trouble.

Stockfish 11 says:

27... Nh3+

(27. .. Nh3+ (♘f4-h3+ ♔g1-f1 ♕c6-e4 ♕d2-e3
♕e4xg2+ ♔f1-e1 ♘h3-g5 ♖b8xb7 ♖d6-e6 ♖b7xf7+ ♔g7xf7 a7-a8♕ ♕g2xa8 ♘a5-c4 ♖e6xe3+ ♘d1xe3 ♕a8xa2 d4-d5 ♕a2-b1+ ♔e1-e2 ♔f7-g7 ♘e3-f1 ♕b1-e4+ ♘f1-e3 ♕e4-h4 ♔e2-d3 ♕h4xh2 ♘e3-d1 ♕h2-g3+ ♘d1-e3 ♕g3-f4 ♘c4-d2 ♕f4-e5 ♘d2-c4 ♕e5-e4+ ♔d3-c3 ♘g5-h3 ♔c3-b3 ♕e4-d4 ♔b3-b4 ♘h3-f2 d5-d6 ♘f2-e4 d6-d7 ♕d4xd7 ♘e3-c2 ♕d7-d5 ♘c2-e3 ♕d5-d4 ♔b4-a3 ♕d4-c5+ ♔a3-a4 ♕c5-a7+ ♔a4-b3 ♕a7-b8+ ♔b3-c2 ♕b8-b5 ♔c2-d3) +13.71/42 204)

score for Black +13.71 depth 42.

Jun-11-20  NBZ: <Brenin>: You are absolutely right. I think he issue is that the 6-second SF analysis provided by CG can mess up sometimes because it does not analyze the position deeply enough. Here, if you ask SF to evaluate the position after Nh3+ Kf1, it rates it at only -1.32, but as soon as you play the next move (Qe4), SF realizes that the position is totally winning for Black (-5.59).

In general, I make sure to double-check any of the SF analysis we get here, because 6 seconds is just not enough for complex positions like this, even for a calculating machine as monstrous as SF.

Premium Chessgames Member
  Predrag3141: <isn't 30 ... Ng5, with threats of Nf3+ in addition to Re6, stronger than 30 ... Nf4?>

I needed to spoon-feed Stockfish with its own suggestion. After its first 4 ply, 28 Kf1 Qe4 29 Qe3 Qxg2+ 30 Ke1,

click for larger view

Stockfish gives

30 … Nf4 (now evaluated as winning at -2.83, a pawn better than after 28 Kf1)

30 … Ng5 (much stronger as you said, at -7.85)

Jun-11-20  TheaN: Long story short, I saw <27....Nh3+ 28.Kh1 Rf6 29.Ne3> where every other defense loses quickly (don't really need to analyze this, <agb> did it). Here I thought I solved the problem completely by playing 29....Nf2+?:

30.Kg1? leads to the brilliant Qxg2+! 31.Nxg2 Nh3+ 32.Kh1 Rf1# as Black solved both the queen defending g2 and the defender of f1 by successfully playing Nf2+ and Qxg2+. However, after 30.Qxf2! I thought 30....Qc1+ won as Black controls the back rank sufficiently. Any interposing on f1 is just Qxf1+ with Rxf1#. But 31.Qg1! +- works as the knight's no longer on h3 (this oversight I missed). Shame, as that ending would have been flashy enough :>

Typically, as I was looking for 'quiet' moves that made the attack on the queenside irrelevant yet missed this rather hidden move. Once you see it, 29....Qe4! is not too difficult yet brilliant and I'm glad <Fusilli> was not as blind as I am :>.

Premium Chessgames Member
  chrisowen: Never look a gift horse in the mouth?
Premium Chessgames Member
  Fusilli: <TheaN> Thank you! As it happens, even though the game was played some years ago, I remember very well seeing everything you posted before I saw the crushing 29...Qe4. I think the puzzle is worthy of a Thursday not because of 27...Nh3+, which is clearly the only shot black has, but because of 29...Qe4.

Incidentally, in the line you gave, in the position resulting from 29.Qg1:

click for larger view has still one more shot in 29...Bxg2+. There, 30.Nxg2 loses to 30...Rf1 (white can still move the h-pawn and hope not to get mated so as to queen the a-pawn, but without calculating I am sure black can either mate or manage to capture the d4 pawn with check and subsequently the a7 pawn), but 30.Kxg2 and it's time to resign for black.

Premium Chessgames Member
  AylerKupp: <<NBZ> In general, I make sure to double-check any of the SF analysis we get here>

You should double check <ALL>classic engine analysis regardless of the time spent in evaluating the next move, whether it's 6 secs or 60 hours. Engines evaluate a move based on the leaf nodes of its search tree, and in each and every instance the evaluation of the moves at the end of the line is based on a shallower search than the moves at the beginning of a line. In the most extreme example a classic chess engine might evaluate the position after White's last move in a search as winning, even though Black might have a mate in one on it's next move. The classic chess engine is simply blind at the end, one type of horizon effect. Check my forum's header for the definition of what I egotistically call AKC2ML (AylerKupp's Corollary to Murphy's Law).

Stockfish in particular is prone to gross mis-evaluations in a shallow search such as the example you gave. This is also commonly evident in it's analysis during on-line chess games; you see it evaluate a certain move in a position as being the best, the player makes it, and on it's next move it evaluates the position much differently than it did a ply before, even though the player made the move it suggested as best. You simply need to let Stockfish calculate longer so that it reaches a deeper search ply than other engines before you can have adequate confidence in its evaluations.

I'm less certain about engines using MCTS if they make their move evaluations conducting simulated game playouts that might continue until either decisive results are found or until positions are reached where tablebase evaluations are possible. But I don't think that any of them do because it takes too much time to do the simulated playouts to the end of each game and I don't think that any of the NN-based engines make use of tablebases.

Premium Chessgames Member
  NM JRousselle: This is lucky escape by Black. White held a crushing advantage for several moves before the blunder 27 Na5. The simple Rb7 (perhaps not the best move) would have simplified White's life by removing counterplay and winning 2 pieces for the rook.
Jun-11-20  Pballa: White was doing quite well until 27. Na5. Had he played Nc5 or Ne3, he would maintain a winning edge. The move that was played allowed for black to find a very nice attack to swing the game.

Also, as Mariano mentioned in a previous comment, white missed a clear edge in the opening on move 8 (8. Bxf6 Bxf6 9. Qh5 g6 10. Qxd5).

Jun-11-20  Nullifidian: 27... ♘h3+ is the key move. Black, naturally, would like to play ♕xg2#, but the queen controls the second rank and so you have to find checks on the squares the queen doesn't control.

If the sac is accepted, then it's a quick death for white with 28... ♕h1+ 29. ♔f2 ♖f6+ 30. ♔g3 ♕f3+ 31. ♔h4 ♖f4+ and mate next move.

If white plays 28. ♔h1, then 28... ♖f6 Δ ♖f1#. The h2 pawn is physically blocked and the g2 pawn is pinned, so there's no way of giving the king some luft. 29. ♘e3 covering the f1 square looks like a good try, but it fails to 29... ♕e4 Δ ♕b1+, and white can't cope with the number of threats to its weak back rank.

So the only tricky part was to find what happens if white tries to brazen it out with 28. ♔f1, bringing his king into the open. The immediate 28... ♖f6+? and ♗a6+? fail to 29. ♔e1, so that gave me 28... ♕e4, preventing the king from coming to the e-file. (It's an oddity of this position that the more exposed the king, the greater is his safety.) Now ♖f6+ and ♗a6+ are deadly threats. White might try to play 29. ♕e3 offering a queen trade to relieve the pressure as well as giving the king a piece to shelter under (29... ♖f6+ in this position would still only draw to 30. ♔e1), but now 29... ♕xg2+ 30. ♔e1 ♘g5! Δ ♘f3+ with the loss of the queen wins. White might respond with 31. ♘f2 to clear the d1 square for the king, but now 31... ♖e6 pins the queen. White has nothing better than 32. ♕xe6 and now 32... ♕g1+ 33. ♔e2 ♗f3+ 34. ♔d3 and only now 34... ♘xe6 preserves black's pieces.

Jun-11-20  Mendrys: <Cheapo by the Dozen: I was even sloppier in my analysis than the game's actual player. :) E.g., I thought that 28 ... Rxd4 would be effective because it overloaded White's queen, quite overlooking that the aforementioned queen can just capture the rook WITH CHECK.>

I did the same thing and now don't feel quite so embarrassed. I think it's easier to overlook this sort of thing when there is so much activity on opposite corners of the board as in this game.

Premium Chessgames Member
  Predrag3141: < In general, I make sure to double-check any of the SF analysis we get here>

The only question is who double checks. I feel free to label lines I give as from Stockfish and leave it at that without double checking. Though I wasn't expecting it to be this wrong!

Premium Chessgames Member
  AylerKupp: <Pedrag3141> Well, I always start out by suspecting that an engine's analysis is wrong until proved otherwise. So when I conduct and engine analysis I'll try to verify it (if I have the time) before I show it to anyone, and the only one available to double-check the engine analysis is me. So I play back the analysis move-by-move and make a note about those times when I think that another move might be better. Then I go back and restart the analysis from those points, perhaps using a different engine to ensure that Stockfish didn't make a mistake by prematurely pruning that branch from its search tree. But, because multi-core engines are non-deterministic, it's like having a different pair of eyes whether you use Stockfish again or another engine. And most of the time I'm wrong and indeed Stockfish played the best move, but sometimes I'm right.

Forward sliding is an effective, although highly time-consuming way, to make sure that an engine's evaluations are not adversely affected by the horizon effect. Then it's a question of deciding at which move to restart the analysis. The most extreme example was used by user <kutztown46> where he restarted the analysis multiple times and each time one ply later. I called this a "creeping barrage" alluding to the bombarding of enemy lines during WW I as the infantry advanced.

Sometimes I do what I call "forward leaping", a play on the words "forward sliding". It's meant to be a quick confidence check and involves starting the analysis at the position reached after the last move in the initial analysis. It's not so much about finding better moves or determining where the engine might have gone wrong but to try to verify the soundness of the initial analysis. If the engine's evaluation after forward leaping is consistent with the initial evaluation, then I have reasonable confidence that the initial evaluation was reasonable. But if it is very different then I conclude that the engine made a mistake somewhere along the way and there were better moves to be made.

In that case my preferred approach in finding where the engine went wrong is to do a binary-like search. Say the engine generates a 40-ply analysis and its principal variation (representing best play by both sides) evaluates the resulting position at [+1.23]. I do a forward leap and let the engine do another 40-ply analysis and it comes up with an evaluation of [+0.12]. Clearly the initial evaluation might have been faulty (it's also possible that it was the subsequent evaluation that was faulty). So I restart the analysis at the position 20 plies from the initial position. If that evaluation is, say, [+1.20], then the analysis after the first 20 plies was reasonable and no obvious mistakes were made by the engine during its evaluation of the first 20 plies. If that evaluation is, say, [+0.10] then the engine seemingly made a mistake during its evaluation of its first 20 plies. In the first case I restart the analysis from the position after the 30th ply since if the engine made a mistake it made in its analysis of plies 20 – 40, and in the second case I restart the analysis on the position after the 10th ply since if the engine made a mistake, it made it in plies 1 – 20.

I then repeat the process each time halving the interval between plies in the initial analysis until I converge to a ply in the initial analysis where I get a significant difference between the initial and subsequent evaluations. That would be the ply where the engine made a mistake in the initial analysis, most likely due either to the horizon effect or a too-aggressive pruning of its search tree.

Someday I hope to be able to automate this process so I can just turn it on overnight and get the desired answer as to what the correct principal variation was when I wake up.

Premium Chessgames Member
  Fusilli: <AylerKupp> That's a very systematic approach. Can I ask what your purpose is, though? Are you trying to find the ultimate truth?

At my level of play (national master, although beyond the 2200 rating now), I run my games by the engine for the very pragmatic reason that I want to either confirm or spot what I did wrong, and confirm or spot what better choices I had. I don't try to answer the question "what was the best move?" unless it's pure tactics, at which any engine is much, much better than me, of course.

IMHO, the ultimate limitation of engines is that they cannot factor in human psychology. From a practical point of view, a suboptimal move may be the psychologically advisable move. What is the point evaluation of tricking your opponent into playing a line that he usually avoids, for example?

In this game, sure, I would have probably lost if my opponent had played anything reasonable but the tempting 27.Na5. But given what I had at move 24 (that self-inflicted disaster), I did pretty much the best available with 24...Qc6 and subsequent moves to maximize my likelihood of swindling the game.

The computer may not agree, because the computer calculates everything and has no psychological factor. So, if one line risks losing the game immediately but creates a trap (what I played) and another line goes into a completely hopeless, lost endgame, the computer will choose the slow death because it assumes the trap will be spotted and foiled.

Another way of putting this is: if line A gives +4 and line B gives +3, black is not necessarily significantly less likely to lose in line B than in line A. Both positions are technically lost. Black is less likely to lose if he plays the line that creates more traps and problems for white. If that line is A, then go for A even if the computer rejects it.

27...Nh3+ didn't come out of a vacuum. I worked on it from 24...Qc6, where each move maximizes piece activity and threats. 24...Qc6 takes control of the diagonal (which means Nxf4 is still available) and frees up d6 for the rook, which needs to be on the sixth rank. Then 25...Rd6 gets to the sixth rank with win of a tempo (the queen threatens the rook). And 26...Nxf4 finally gets the knight where it should be. But the computer prefers 25...Nf6 or 25...Rc7 to 25...Rd6. From a human point of view, neither makes sense to me.

Premium Chessgames Member
  AylerKupp: <<Fusilli> Can I ask what your purpose is, though? Are you trying to find the ultimate truth?>

Yes, that's one purpose. But I should say "goal" since I realize that the ultimate truth is unattainable. My second purpose is to learn and figure out why the computer suggested a particular best move but that's not an easy thing to do. I've felt for some time that, since all the information is available that the computer uses to determine what the best move is, you should be able to request it and have it presented in a simpler, human-understandable way. In older rule-based system you had an expert or set of experts define appropriate rules and let the computer decide which, often conflicting, rules to use. You could then query the computer for it to tell you why it evaluated a particular answer to be the best.

But that's not likely to happen with commercial chess engines because the details of their evaluation function are considered proprietary, and a wonderful learning opportunity is lost.

<IMHO, the ultimate limitation of engines is that they cannot factor in human psychology. From a practical point of view, a suboptimal move may be the psychologically advisable move.>

User <Sally Simpson> and I have had many discussions along the same lines. While it may be true that a classic chess engine will not play anything other than what it evaluates to be the best move (although it will suggest as many second, third, etc. best moves as you ask it to, within reason), I don't think that it has much practical significance. Currently engines only play against other engines and humans only play against other humans. And if in a reasonably lost position an engine tries to fool the other engine and tries to swindle it by playing other than the best move, it will not likely fool the other engine at all. The winning engine will select the best move to play in response and, the losing engine will simply lose more quickly.

Only in games between humans and engines, when the engine finds itself in a losing position, would an attempted swindle by playing objectively worse moves would make sense. But how a engine capable of superior play find itself in a losing position in the first place?

And I'm sure there are exceptions but I doubt that there are many. Now, developers of chess engines that use MCTS instead of minimax to determine which move to make claim that the engines play more "human like", as though this is something to strive for. Well, for some it is, but not to me. The fact is that for sometime when a human plays against a chess engine the human will likely lose, unless the engine is operating under a material or time handicap or both. So, if the objective is to win, I don't see much virtue of having the engine play "human like" moves which may not be necessarily the best and increase its losing chances.

<Black is less likely to lose if he plays the line that creates more traps and problems for white.>

True if Black is an engine and White is a human. But if White is also an engine the only near certainty is that Black will lose more quickly since the White engine will see through the trap. And the same thing if it's a human(s)+engine(s) vs. a human(s)+engines(s) as some of the <>'s Team Challenge games have been conducted. If the Black human(s)+engine(s) team is in a losing position, the engine(s) will suggest that the move that delays the loss as much as possible is the "best" move to play, even though it loses material (one version of the horizon effect). But the White human(s)+engine(s) team will not be fooled if they are relying on their engine(s) to identify the best move to play in response.

Premium Chessgames Member
  Fusilli: <AK> I agree on everything. My comments were from the point of view of someone who uses engines to check on the quality of his play. Not from the point of view of the engine as a chess player. You are absolutely right in all the distinctions you make re: who is playing against who.
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