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Mutual Damage
   

[Diagram]
Diag.: Mutual damage

Black 1 is a typical endgame hane, which threatens to heavily damage the opponent'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.


[Diagram]
Diag.: No mutual damage

Locally, the sequence comes to an pause after 4 and Black has sente. He then uses his sente to execute another endgame hane.



Experienced players will agree the game is finished after White 8, 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.

[Diagram]
Diag.: Mutual damage

Mutual damage is in fact an application of the miai concept to the endgame. The moment Black plays 1 to damage White's territory, White MUST play the equivalent play at 2, if only out of self respect.

BillSpight: W 2 and answering B 1 are worth about the same. However, as Dieter says, White cannot afford to let Black get both hanes. It looks like White should play W a - B b before W 2. If Black has to play both points later, W 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 Costly Atari.


[Diagram]
Diag.: Even

If Black answers White's hane, White keeps sente to defend against Black's hane at 6. The game ends after White 8 and White wins by 1 point.



[Diagram]
Diag.: 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 never the situation 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 W c threatens a snapback at d.



Still, if one player docilely 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.


Authors: DieterVerhofstadt



This is a copy of the living page "Mutual Damage" at Sensei's Library.
(C) the Authors, published under the OpenContent License V1.0.