Interesting finish to a game

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Christopher Kreuzer
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Re: Interesting finish to a game

Post by Christopher Kreuzer » Wed Apr 07, 2021 4:57 pm

Roger de Coverly wrote:
Wed Apr 07, 2021 10:24 am
Christopher Kreuzer wrote:
Wed Apr 07, 2021 10:05 am
Win for Black:
There's an obvious winning plan of K-c4-b5-a6(or c6) and then Qxb7 mate.

That works if the Black King just shuffles between b8 and a8. If however it tries to escape with .. Ka7 and .. Kb6, White has Qb5 putting the King back in the zugswang box and enabling the White King to advance.

In normal circumstances King and b pawn loses to King and Queen. The extra material seemingly can make a difference by controlling a7,b6 and c5.
There must be more to it than that. Why is the position with the Black king on f8 a draw? There is some form of triangulation going on maybe? With the king on f7, the win involves going to e6 (rather than e8), and that doesn't work from f8 (I think - I need to set that position up again). I think it involves the queen needing to be able to access certain squares. But then the question is why can't the king from f8 get to one of the other squares to get the win? It must be because White is close to setting up a drawing plan (involving the a-file in some way), and Black still needs to disrupt that, and only has limited time in which to do so. What White often can't do is return to c8. The tricky thing for White is knowing precisely when to move king or bishop, if for example Black dances the king around on the g-file or h-file or 1st and 2nd rank (all those squares are draws) and only approaches a 'winning' square when White might be short of time and might forget the right sequence of moves. Or is it simpler than that?

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Christopher Kreuzer
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Joined: Fri Aug 06, 2010 2:34 am
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Re: Interesting finish to a game

Post by Christopher Kreuzer » Wed Apr 07, 2021 5:20 pm

There are some other similar 'pairs' of positions where the Black king position matters a great deal, but am still not quite sure why. Maybe there is a key position where the White bishop needs to move, thus making it impossible for the Black king to approach any closer, and also making it impossible for the Black queen to force zugzwang.

Interestingly, the White bishop does NOT need a pawn somewhere to support it. The 'pure' position with just b-pawn and bishop is probably well-known to endgame specialists. A simple example is below.

Black to move. Drawn.



(After 1...Qb8 White has only one move to draw.)

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