Throw In or Not

  Difficulty: Advanced   Keywords: Tactics

The question arose on the oiotoshi/discussion page about whether Black should make a throw in before an atari in a certain position. A difference game can help us answer that question.

Difference Game  

Black merely plays the atari at B1, while White starts with the throw in at W2. Which player stands better after W4, if either does?

In the difference game we compare results when each player plays first.

Black plays first  

B7 takes the ko. Even if White wins the ko, Black wins by 1 point because of White's captured stone. (W2 could also be at W4, with the same result.)

White plays first  

White's best play is W1, winning the 4 black+circle stones. Then Black throws in at B2 and catches up to White with B4. Now Black can stay even by copying White's plays.

Black to play wins the difference game, while White to play does not. So Black stands at least as well as White. Playing the atari without playing the throw in first is correct. The only possible exceptions require a ko somewhere else on the board.

--Bill Spight

Throw In or Not last edited by BillSpight on November 22, 2004 - 18:34
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