Wednesday, August 29, 2007

Rook Pawns & Outside Pawn II

Yesterday I covered eight Rook Pawns & Outside Pawn endings. You may wish to familiarize yourself with that blog entry before proceeding.


Speelman-Chandler, Hastings 1988. White to move. Quick! Who wins?

The techniques we discussed in our last lesson don't help. White's rook-pawn hasn't crossed the middle of the board, and counting isn't easy because the paths of the two kings cross.


What can we do? We can use a new technique called Bahr's Rule. Draw a diagonal line from the defender's pawn towards his first rank. Then, at the bishop file, bend the line back towards the attacker's first rank.

If the attacker's passed pawn is on or behind the line, he wins. If the attacker's pawn is in front of the line, he draws. So in this case White draws.


Mecit-Acosta, Dos Hermanas 2004. Black to move. Quick! Who wins?

Again, let's draw the Bahr's Rule lines:



The attacker's pawn is on the line, so he can win with accurate play! In the actual game, Acosta played the inaccurate 56...f4+? and drew. The right plan for Black was to capture White's a-pawn and then promote his own.

Bahr's Rule is very useful, but only use it when the attacking king is beside his passed pawn and the defending king is in front of it.



Sutovsky-Gulko, Montreal 2006. White to move. Quick! Who wins?

I told you Bahr's rule only works if the attacking king is beside his passed pawn and the defending king in front of it. Clearly, that's not the case here.



But Bahr's Rule works with a slight modification. If the attacking king is in front of his pawn, and the pawn is not a rook's pawn, pretend that the pawn is one square further back before applying Bahr's rule. This position is actually a win for White.

4 comments:

Sciurus said...

Fascinating. I played a bit with the examples using the tablebases at Shredderchess.com. In the second example (Mecit-Acosta, Dos Hermanas 2004), the rule you explain is totally against my instincts - if you move the black pawn & the kings one square closer to promotion, it becomes a draw, just like the rule predicts. And I always assumed that being closer to the promotion square is a good thing! Furthermore, in the example every move but the pawn move wins. Even moving the black king to the h-file wins. Fascinating, even though I still don't know if I'll ever remember that.

likesforests said...

Acute observations. It's hard to remember a rule that runs contrary to our instincts, so just for you, I've broken down this endgame in great detail in my next post. I like to move the pieces up, down, and around to see what impact that has on the final result. I think doing that (as you are) is a great way to learn.

pablito15 said...

When you say:

"If the attacker's passed pawn is on or behind the line, he wins. If the attacker's pawn is in front of the line, he draws. So in this case White draws."

What exactly do you mean by "on or behind?

In the example you've given is anything on the 3rd rank (apart from g3 & h3) "behind" the attackers pawn? And when you say "on" the line, does that literally include on the squares d5, e4, f3 etc?

I find that the explanation of this rule in books is always in really ambiguous language- anyway, thanks for your help, I've linked your site on my blog:)
Thanks,
Paul

Anonymous said...

This is the best explanation of Bahr's rule I've seen. Well done !