Add a second stone and sacrifice both

Paths: <= Aspects of Sacrifice => · <= Forcing and initiative => · <= Go Proverbs =>

Keywords: Proverb

The proverb add a second stone and sacrifice both summarizes a common technique of sacrifice. Adding a stone has many possible effects:

increase liberties and require the opponent more moves to capture.
make opponent's eyespace less efficient.
induce opponent's capturing moves touching to the edge, thereby reducing liberties.
make later atari not a ko.
make a meaningful recapture.

Table of contents
Increasing liberties

Making eyespace less efficient

Reducing opponent's liberties

Making later atari not a ko

Making a meaningful recapture
Table of diagrams
Crosscut
Add a second stone
Kikashi
Direct atari: not so good
Direct block: also not good
Summary
Simple example
sacrifice
one point in gote

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Increasing liberties

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

Black has just played the crosscut at . (Sakata calls 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.)

It is clear that black+circle is going to be captured. Nevertheless Black adds another stone, in accordance with the proverb.

The thinking behind Black's line of play becomes clear in this diagram. Black has forcing moves at , and . Thanks to his larger sacrifice, he has a move on the outside () and two which seal off the corner. (Note that makes a a gote follow-up for White. See /continuation for further explanation.)

Compare this with an atari at 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.

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

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.

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Making eyespace less efficient

The simplest example is this corner shape. If Black is allowed to play at 1, he secures two eyes very efficiently. White simply adds a stone to be captured. Two stone capture consumes more eyespace for making an eye.

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Reducing opponent's liberties

See Two-stone edge squeeze and Two-stone corner squeeze.

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Making later atari not a ko

See Gokyo Shumyo, Section 1, Problem 74 / Solution. White avoids a ko by adding a sacrifice stone (see the first Variation diagram).

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Making a meaningful recapture

For example, Long L group with an outside liberty can only live by adding a sacrifice stone. See Diagram titled Variation 2.

Another example is from late endgame:

If Black plays at 1, he has two points of territory. White lures Black stone at 2 and recapture.

Black has got two prisoners and White one; is worth one point in gote.

Paths: <= Aspects of Sacrifice => · <= Forcing and initiative => · <= Go Proverbs =>

Add a second stone and sacrifice both last edited by hnishy on April 27, 2020 - 13:34

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