From a position in this puzzle:
https://lichess.org/training/65234
Stockfish evaluates the position after 29. Kh1 as 0, or dead even. But 29... Qh4+ gives Black a forced mate in 2. And when played, Stockfish changes its evaluation to reflect this (#-2).
Stockfish even has 29... Qh4+ next move as its second choice, so it definitely sees it. But for some reason it prefers 29... Qh3+, which only leads to an even exchange of material.
Edited to add after laatikko's comment, 29... Qh3+ would be a draw by repetition of positions from Black's moves on move 25 and move 27. This still doesn't explain the 0 evaluation from 29. Kh1, as this is only the second time that position has been reached as well, matching the position from 27. Kh1. And the position after 29... Qh4+ had not been reached at all, so that's not a reason it would evaluate 29. Kh1 as 0, either.
One last thing. When I refreshed the puzzle, 29... Qh4+ was now the preferred move over 29... Qh3+. But the evaluation is still 0, when there is an obvious mate in sight. Pretty odd to me.
There's a threefold repetition. If you backup before that, it'll give you mate -3#.
It sure is @laatikko but you should notice that aside 29...Qh3+ only 29...Qh4+ is evaluated as 0.00. I can't see any reason for that.
@rizka10 I see, that's pretty weird indeed. Maybe the 3-fold upsets sf. I wonder what that evaluation means, surely sf would find a mate had it to continue from this position (after 3-fold) instead of just claiming a draw (?)
29... Qh4+ would not have been a 3-fold repetition, so I'm not sure what you're saying here laatikko. There haven't been any 3-fold repetitions I can see. I only see instances of 2-fold repetition with:
25... Qh3+ and 27... Qh3+
26. Kg1 and 28. Kg1
26... Qg3+ and 28... Qg3+
Maybe I'm missing something, can you list the 3 moves any position was repeated 3 times?
After 25 Qxd4 the black queen is on g3.
After 26...Qg3+ it is on g3 again
After 28...Qg3+ it is on g3 again.
So the same position was on the board 3 times with the same player to move, so white could have claimed a draw. Thus evaluation 0 = draw.
After White's moves 25., 27. and 29. the same position occurs.
tpr,
on 25. Qxd4, the White King is on h1 and it is Black's move.
on 26... Qg3+ and 28... Qg3+, the White King is on g1 and it is White's move.
This is not what threefold repetition means, that because the Black Queen is on g3 3 times, it's a repeated position. It has to be exactly the same position, and it's not in your examples.
Edited to add again after laatikko's comment, I see now after you list those moves rather than the ones tpr listed. You are quite correct, I understand now. Thanks guys. This was like a puzzle within a puzzle.
The rules are different. In this case white would have to write down his move 29, then notify the arbiter and claim the draw. If white executes his 29th move on the board, his chance of claiming the draw is gone.
Well this is rather confusing. I tested this by playing the position against myself and lichess allows White to claim the 3-fold repetition only after 29. ...Qh3+ 30. Kg1.
Why is it not threefold after 29. Kh1 ?
The same position has occurred three times.
And if it is not draw by threefold, then why does stockfish evaluate it as 0.0?
All in all, the question why both 29. ...Qh3+ and ...Qh4+ are being evaluated as 0.0 but eg. ...Rg8 gets +4.1 remains unsolved.
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