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The following tactics problem is problem #97369 from ChessTempo. It is a position from a game between Yuri Yakovich and Pavel Kotsur. It's black's move.

The idea of the tactics problem is to find black's best move from the shown position.

But my question is slightly different: If both players play perfectly from the position shown in the diagram, can black force a win, or can white force a draw?

[FEN "6k1/5p2/1Pp3pb/2q4p/1rNpPP2/3Q2PP/8/5RK1 b - - 0 1"]

I tried using a couple of chess engines to analyze the position. The lines they suggested gave black a positive score, but didn't seem to give a forced win.

So what do you think: is it a theoretical win for black or can white escape with a draw?

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Which chess engine, and what did it say? –  Tony Ennis May 23 '12 at 0:57
    
@TonyEnnis: I tried a couple. After a few hours Stockfish says "D32 +2.34 1... h4 2. Ne5 Qxb6 3. gxh4 Bg7 4. h5 gxh5 5. Qf3 Rb1 6. Qxh5 Rxf1+ 7. Kxf1 Qb5+ 8. Kf2 Bxe5 9. fxe5 Qb2+ 10. Ke1 Qc1+ 11. Ke2 Qc2+ 12. Ke1 Qxe4+", but I don't fully trust the computer's evaluation for this sort of situation. I'm not even sure that the first move is correct. –  Mark Byers May 23 '12 at 4:51
1  
When I've done this, I let the computer play itself. If the sequence of moves is stable and the points don't change unexpectedly, I feel the moves are reasonable. What first move did you expect? The obvious move 1. ... Qxc4 2. Qxc4 Rxc4 3. Rb1 Bf8 4. e5 looks rough for black. 1. ... Rxc4 may be the better else the N gets to e5. I don't see a good follow up though I've only spent about 30 seconds looking at it. –  Tony Ennis May 23 '12 at 11:23
    
I do not play perfectly nor do I know of anyone or anything that does it. I do not see a forced sequence of moves leading to a theoretical drawn or won/lost position. I think your question is asking too much. –  Ray May 23 '12 at 13:11
    
Understood. If it's not possible to find a forcing line, I'd be happy with just knowing what the best move is and perhaps an explanation of why it is better than the alternatives, or some ideas for how white can play towards a likely win, or black can best defend to get a draw. –  Mark Byers May 23 '12 at 16:08
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2 Answers

up vote 7 down vote accepted

I think it's a forced win for black.

Black can start with 1...Qxc4 after which the next five white moves are forced to avoid a fast loss.

[FEN "6k1/5p2/1Pp3pb/2q4p/1rNpPP2/3Q2PP/8/5RK1 b - - 0 1"]

1...Qxc4 2.Qxc4 Rxc4 3.Rb1! Bf8! 4.b7! (4.e5!? d3 5.b7 d2 6.b8=Q Rc1+ 7.Kf2 d1=Q) Bd6! 5.b8=Q+ Bxb8 6. Rxb8+ Kg7

Black is a pawn up and has connected passed pawns and should try to exchange pawns to simplify to a won end-game. The game might continue for example as follows:

[FEN "1R4k1/5p2/2p3p1/7p/2rpPP2/6PP/8/6K1 b - - 0 6"]

6... Kg7 7.e5 c5 8.Rd8 Rc3 9.Kf2 h4! 10.gxh4 Rxh3 11.Rc8 Rc3

The computer still doesn't find a line that leads to an obvious win but it looks like a hopeless situation for white and the computer playing against itself gives a win for black. Here's an example way to continue the game:

[FEN "2R5/5pk1/6p1/2p1P3/3p1P1P/7r/5K2/8 b - - 0 11"]

1... Rc3 2. Rc7 Kf8 3. Ke2 c4 4. Kd2 Rf3 5. Rxc4 Rxf4 6. Rc8+ Kg7 7. Rc7 Re4 8. Re7 Rxh4 9. e6 Kf6 10. Rxf7+ Kxe6 0-1

The final position is a table base win for Black.

If you think there any errors in this analysis (in particular, weak moves for white that changed the value of the position from drawn to lost) then please let me know.

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At the risk of being no fun whatsoever, what does Rybka or Crafty have to say about it? –  Tony Ennis May 26 '12 at 14:23
1  
I could give my opinion all day long, but in the end I'm a B-player. I basically have no chance of defeating someone who has no chance of defeating a strong program. –  Tony Ennis May 26 '12 at 15:19
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To answer your question directly, I don't think this is a theoretical win or draw. The reason is that the game is still too up-in-the-air. There may be a forced win for one side or the other, but that's not the same thing.

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I want to know if there is a forced win for black and some demonstration of how black should play in order to win. I'd be quite happy just knowing what the first move is. The computer suggests a few alternatives but it's not clear which of them leads to a win, if any. –  Mark Byers May 25 '12 at 18:47
    
Please take a look at my answer to see if you agree with my analysis that it is probably a forced win for black. –  Mark Byers May 26 '12 at 14:09
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It not being a theoretical win or draw (I agree) doesn't prevent it to have a theoretical status, either win/draw/lose, enforced by optimal play (as opposed to the rules). –  Nikana Reklawyks Dec 1 '12 at 1:18
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