Ko Fight Example From A Pro Game - 2

Move 158  

This is the final game in the 2011 Myeongin title match, between Park Younghun and Baek Hongseok. Park has White in this game. He played 158 at , turning his captured group in an unbalanced kind of ko: it's a one-move approach ko advantageous for Black, but at the same time a hanami ko for White.

The whole issue is whether White is thick enough on the board to ignore multiple ko threats, so that the profit of winning the ko outweighs those threats. First, we have to understand the local situation and why it is ko at all.

The ko  

If Black plays conservatively, covering his weaknesses at and , turns the life and death status of this group into ko. Given the whole board position, this is unbearable for Black. He must fight.

The ko  

If Black occupies the vital point of White's group, White cuts at and threatens to capture at a or b, making the ko very heavy for Black. (Black can also avoid the ko at a considerable cost: see ^[1])

Moves 159 to 168 ( @ ) ( at ) ( at )  

So, takes the ko first in order to finish the capture as soon as possible. A typical ko cycle? develops, with White alternating between threatening to make big profit () and even killing a group (), while Black is almost obliged to generate big threats, like which turns the white corner into an L+1-group.

Moves 169 to 178 ( at )  

is another big threat, while is aiming at free endgame again. is a different kind of ko threat: those stones where dead anyhow and although the follow-up of a is not small, the main purpose of is to remove ko threats. This invites White to enlarge the ko at , instead of merely trying to live at b. of course retakes the ko. is again a big threat, ...

Moves 179 to 188 ( at )  

... against which defends. When takes the ko, Black has a local response available: cannot just connect at , since Black would have the time to kill at a. - continues where White was threatening before. Black has run out of really big threats, although I'm interested in evaluating b. Anyway, Black uses the thickness he created a few moves ago on the right to cut White on a large scale. White is however unimpressed and makes a turnaround at the bottom imminent.

Uberdude: The reason white can ignore is he made the preparatory marked kikashi before starting the ko (about 40 moves ago, pros read deeply!). See my analysis at http://www.lifein19x19.com/forum/viewtopic.php?p=85718#p85718

Moves 189 to 198  

So Black seems to have no choice but resolving the ko with and . White has reserved a major threat and kills the upper left corner. So, the net result is that Black has finished off an already dead group at the bottom while White has killed a big group, with a profit of about 35 points. Black now has to prove that his successive moves on the right side can launch an effective attack on White's position, but White skillfully sacrifices some stones.

Moves 199 to 208  

Indeed, after the exchange on the right side has been done, White restoring his connection in exchange for a relatively small side, Black must come back at to clean up the last aji from White's skirmishes down there. White takes the big point of and the game is over. A few moves later Black will resign.

Conclusion

This ko fight is an example of lose a ko to win the game: although the ko was an approach ko for White, in which he had to ignore multiple threats, in the end the size of it was so big that Black had to come back and win it, so that White could play two moves elsewhere. Thanks to White's overall thickness, Black's two ko threats, which were ignored, were not big enough in comparison.

[1] This variation avoids the ko completely, but perhaps deemed too submissive for black. -- Vesa 5 dan