Add a second stone and sacrifice both

    Keywords: Proverb

The proverb add a second stone and sacrifice both summarizes a common technique of sacrifice.

Table of contents Table of diagrams
Crosscut
Add a second stone
Kikashi
Direct atari: not so good
Direct block: also not good
Summary
Nearby stones
Options
Kikashi
Gote
Gote
Tenuki

Main discussion

Consider the following sequence (discussed by Sakata Eio in his book "The Middle Game of Go").

[Diagram]

Crosscut

Black has just played the crosscut at B1. Sakata calls B1 vulgar style in the context of the discussed game, but that is another matter. There are plenty of occasions where this sequence is perfectly OK.

[Diagram]

Add a second stone

It is clear that black+circle is going to be captured. Nevertheless Black adds another stone, in accordance with the proverb. White answers at W2 to maintain the kill of these cutting stones captured.

[Diagram]

Kikashi

The thinking behind Black's line of play becomes clear in this diagram. Black has forcing moves at B1, B3 and B5. Thanks to his larger sacrifice, he has a move on the outside (B1) and two which seal off the corner (B3 and B5, the latter making a a gote follow-up for White).

[Diagram]

Direct atari: not so good

Compare this with an atari at B1 without adding the extra stone: White would capture (a ponnuki), and that would be the end of it. The block at a is no longer sente now.

[Diagram]

Direct block: also not good

If B1 simply blocks, W2 will capture and the atari at a is no longer there.

[Diagram]

Summary

In summary: adding the extra stone increases the (marked) liberties of the black group. As White needs more moves to capture it, Black gets more forcing moves.


The effect of nearby stones

[Diagram]

Nearby stones

For the sake of discussion, if there is a white+circle stone, then White will almost always capture black+circle by W1 (ladder), and almost never play W1 at a. This leaves only the aji at b, but the block at c is not sente.


More on the effect on thecorner

[Diagram]

Options

Let's look at three options. a, b and tenuki.

[Diagram]

Kikashi

If Black at B1 here, B3 can play tenuki. W4 ends in gote. Later there is the alphabetized endgame.

(Of course, if black is komaster, black could respond to white a with black c. But in general, black has to draw back to b because white will have little to lose in the ko.)

[Diagram]

Gote

If Black does not play tenuki, he ends in gote. We can expect White a, Black b, White c in the late endgame.

(When compared with the sente diagram above, B3 here is worth only about 9 points in gote. Before yose, this is relatively small, so tenuki is most likely a better option.)

[Diagram]

Gote

Black gives up the possibility of tenuki and ends up in gote anyway. In the endgame we can expect Black a White b Black c.

[Diagram]

Tenuki

If Black plays tenuki, W1 can be sente.

The third part may be explained elsewhere already


This is a copy of the living page "Add a second stone and sacrifice both" at Sensei's Library.
(OC) 2008 the Authors, published under the OpenContent License V1.0.
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