Mutual Damage

  Difficulty: Intermediate   Keywords: EndGame

Chinese: 互破 (hu4 po4)
Japanese: -
Korean: -

Table of contents Table of diagrams
Question starts here
No mutual damage
Mutual damage
Bill's idea
B defends - loss by 1 point
Mutual damage
Road to White's win I
Road to White's win II
Mutual damage -- better for b?

Introduction

The general principle of mutual damage is to accept loss of territory, rather than defend territory, provided one can inflict equivalent damage on the opponent. Hence, mutual damage is a kind of exchange.

Defending is a way to accept gote. If you pursue a mutual damage plan, not answering the opponent's destructive plays directly, the possession of sente is actually in the balance for a while. You only find out who has it when the dust settles.

A mutual damage contest can be set off by miai: one player doesn't accept the idea that the other will get both of a pair of closely equivalent plays that are ordinarily sente. It can end in a game of 'chicken' (less colloquially, who blinks first).

Mutual damage in the opening is unusual.


An endgame which mutual damage is needed

[Diagram]
Question starts here  

B1 is a typical endgame hane, which threatens heavy damage to White's territory if unanswered.

BillSpight: It is also what is normally called a double sente. It is worth around 9 points (miai), I believe, a huge play.


No mutual damage - loss

[Diagram]
No mutual damage  

Locally, the sequence comes to a pause after W4 and Black has sente. He then uses his sente to execute another endgame hane.



Experienced players will agree the game is finished after White W8, and it is easy to see that Black wins by 3 points. It feels not entirely fair that Black has been able to play both hanes. Indeed, White has failed to apply the principle of mutual damage.


Mutual damage - may win

[Diagram]
Mutual damage  

Mutual damage is in fact an application of the miai concept to the endgame. The moment Black plays B1 to damage White's territory, White must play the equivalent play at W2, if only out of self respect.



BillSpight: W2 and answering B1 are worth about the same. However, as Dieter says, White cannot afford to let Black get both hanes. It looks like White should play White a - Black b before W2. If Black has to play both points later, White a is aji keshi, but both sides will be invading, and this may be White's chance to inject some aji into Black's position. A difficult question.

See also Costly atari.

[Diagram]
Bill's idea  

Willemien just giving Bills idea (as written above) a diagram how will this end?

If B defends - loss

[Diagram]
B defends - loss by 1 point  

If Black answers White's hane, White keeps sente to defend against Black's hane at W6. The game ends after W8; and White wins by 1 point.


If B damages W too

[Diagram]
Mutual damage  

One reason many players fail to apply mutual damage, is that the situation can become very confused if either player refuses to give in as in this diagram.



Another reason is that the situation rarely is as symmetric as in this simple example. Even here it isn't quite symmetric: White a is atari whereas Black b is not.

BillSpight: And White c threatens a snapback at d.

aLegendWai: A difficult question. But who will win finally?

celebrir: I guess White is winning

Andy: Because of this extra snapback aji in the black position on the bottom, I wonder if B1 would be more correctly played at W2? [100]

[Diagram]
Road to White's win I  

A interesting thing is, that defending with B5 at a results in a bigger lose for Black. At least in my variations.

[Diagram]
Road to White's win II  

Now White leads with two points on the board + komi. So there is at least enough chaos to take the advantage.


Still, if one player passively answers all "sente" endgame moves by the other, he or she follows a sure path to defeat.


TakeNGive (10k): Wow -- somehow I had never noticed this. Suddenly, BillSpight's endgame analyses take on new value.


Links:


[100]

[Diagram]
Mutual damage -- better for b?  

Is this a better line for black? The black+square stones aren't threatened by W2.


Authors:


Mutual Damage last edited by AndyPierce on May 5, 2011 - 15:55
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