Double Sente is Relative

    Keywords: EndGame, Strategy

Bill Spight:

Double sente is relative. It depends on what else is on the board. Every Go position can be categorized as sente, gote, or ambiguous. Any play, whether a sente or gote in the abstract, can be a double sente if the reply when either player makes the first play is larger than anything else on the board. Usually, double sente are played as soon as they arise.[1]


Example 1

Example (outer stones alive):

[Diagram]
"Double" sente  

This appears in Kano's Yose Dictionary. He says that it is a double sente, but that Black's play has more "necessity". (It threatens White's group.)



Actually, this is a seven-point sente for Black. If Black plays first, we get

[Diagram]
Black sente  

which has a local score of 5.



If White plays first, we get

[Diagram]
White reverse sente  

which has a local count of -2 (2 points for White).



Later this is White's sente.

[Diagram]
White sente  

B2 is tesuji.

And even later, this is Black's sente.

[Diagram]
Black sente (2)  

The local score is -2.



After White's hane, Black's reverse sente is worth three points.

[Diagram]
Black reverse sente  

The local score is 1.



The original position is a seven-point sente for Black. However, when the ambient temperature drops below 3 points, it is double sente (as a rule). However, Black is unlikely to allow that to happen.


Example 2

Beware of so-called double sente. For instance, Kano's "Yose Dictionary" gives the following as a two-point double sente (p.30).

[Diagram]
Double sente???  
[Diagram]
Black sente???  



After the exchange of B1 - W2, White has a one-point sente sequence with W4 - B7. The score is +5 (for Black).

[Diagram]
White sente???  



After the exchange of W1 - B2, Black has a one-point sente sequence with B4 - W7. The score is +3.

If this is a double sente, then whoever plays it picks up two points (by comparison) for free.

But do not be misled. This is actually a gote play, worth about 3 2/3 points (miai value).

[Diagram]
Black's follower  



After B1, B3 is a gote play worth about 2 1/4 points. If there are bigger plays on the board, White is unlikely to respond to B1.

[Diagram]
White's follower  



After W1, W3 is worth slightly more than 3 points.

So if there are plays worth between about 3 2/3 and 3 points elsewhere, Black is unlikely to respond to W1.

This is a middling gote play. Do not think of it as a double sente.

Also see How Big is the 6 point Double Sente


[1]

Tas: Which is why they actually ought to be considered part of a larger sente or gote sequence, although it might be outside anyone's reading ability.

Bill: Well, the examples on this page have theoretically shorter sequences than the double sente sequences. :)


Double Sente is Relative last edited by 68.122.14.149 on December 7, 2014 - 06:24
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