Capture two, recapture one

  Difficulty: Beginner   Keywords: Tactics, Go term

Chinese: 打二还一 (da3 er4 huan2 yi1)
Japanese:
Korean:

The phrase capture two, recapture one describes the sequence below. Note that this is not a ko.

[Diagram]
Dia. 1: Capture two, recapture one.  
[Diagram]
Dia. 2: Capture two, recapture one.  

B1 captures two White stones...

[Diagram]
Dia. 3: Capture two, recapture one.  

... and W2 recaptures the B1 stone.

W2 is a legal move even if played immediately after B1.

Also, this sequence gives no eye to Black.


Endgame Value

The position (Dia. 1) is a 2 point ambiguous endgame. The value and timing is similar to that of ordinary 2 point gote endgames.

There are three possible lines of play:

  1. White connects - score: 0 points.
  2. Black captures two (Dia. 2), White recaptures one (Dia. 3) - score: 1 point.
  3. Black captures two (Dia. 2), Black connects - score: 3 points.

If the score of the third outcome was greater than 3, it would be sente. If it was less than 3, it would be gote with gote follow-up. However, the actual value is exactly on the limit, which makes it ambiguous.

After black captures (Dia. 2), the position has a count of 2 (the average score of the two possible continuations). This means, the initial move and the follow-up (in case black moves first) both have a value of 2 points.

Since the value of the follow-up is exactly the same as the value of the initial move, white will usually respond to the black capture as shown in Dia. 3.

Depending on who plays first, the total number of 2 point endgames on the board changes. This can be used to get Tedomari, as demonstrated in this [ext] problem.

Equivalent positions

In terms of endgame, the following position is equivalent to "Capture two, recapture one" (Dia. 1).

[Diagram]
Dia. 4: Equivalent endgame  


"Capture two, recapture one" in live and death situations

There are a lot of situations where this sequence is a possible variation, the consequences of which are easily overlooked. An example:

[Diagram]
Black to live  

Black to live. The combination of the marked shape with the 1-2 point is very common in life and death problems. Yet our desire to atari may overcome us:

[Diagram]
Mistake by both  

This is a line easily visualized and often played by both players if they fail to see the meaning of this shape.

[Diagram]
Black punished  

White plays W2 and recaptures a stone with W4 at white+circle after B3 takes two stones. Black is dead.

[Diagram]
Correct  

Black's correct move is the 1-2 point. White can't play W2 at a due to shortage of liberties. If White next b, Black a gives life.


See also:


Capture two, recapture one last edited by tamingo on September 9, 2016 - 10:56
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