Ko Fight Example From A Pro Game 4

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[Diagram]

Position at move 177

This is the first game in the 2011 final of the Olleh KT cup, between Lee Sedol (White) and Lee Changho. The older master has shown signs of a come back in 2011 so when he eventually won this first game, his fans were all enthusiastic. In the end, Lee Sedol swept it clean with a 3-1 victory.

We're at move 176: White has just played white+circle to make his group alive, be it that the group's status is decided by a ko at a. The ko is actually very big, because the black stones in the centre can be captured if White lives and also White has some threats on the right side. It seems like an all deciding ko.

However, White needs this ko more than Black does. In fact, the situation is a result of White overplaying a little at the right side, since he needed to catch up with Black's gigantic territory on the left side. In my opinion, White got into trouble because he overplayed at the left in the beginning.

Now to the ko fight

[Diagram]

Moves 177 to 186 (7 at 1) (10 at 4)

B1 takes the ko. We can see that White uses the aji of the captured stones on the left with ko threats W2 and W8. Black's ko threat B5 is smaller in size, but since he has less to lose from the ko, it's surely big enough. If he captures those stones, the central stones are less vulnerable and also the top left becomes very small.

[Diagram]

Moves 187 to 189

After Black's second ko threat B1, something interesting happens: W2 resolves the ko? but Black does not immediately capitalize on the ko threat. Instead, he launches a second ko with B3, trying to fix the result by capturing at a or b. Apparently this would be enough for Black.

[Diagram]

Moves 190 to 193

W4 takes the ko, B5 continues where he left his previous threat, W6 resolves this second ko and B7 completes the ko exchange.

In effect, White has captured 13 black stones in the centre, converting some neutral points into territory too, and his own group of 15 stones is alive, with some extra points by being able to play strongly in that area. The value of the successive kos is an estimated 70 points.

As a compensation, Black converted a White territory of about 30 points in one of his own, an estimated value of 60 points.

Lee Changho being a master of endgame he probably calculated this ko exchange would be sufficient for victory. Black won the game by a 2,5 point margin.



Discussion

Tapir: These series do a great job in emphasizing certain aspects of ko fights one by one.

I believe B189 wants more than to fix the result at a or b. It is all about a a Black move there is huge, not only saving the center stones but directly threatening to cut off the White stones in the upper right. (A sente ko?) If White gives in by connecting at a it would leave behind a smaller ko to save the center, which he would not finish now - otherwise Black would have lost the ko in gote without getting anything in return - but follow up on the ko threat instead, which is bigger than the Black center.

However, it isn't at all clear to me then what B189 gains, as opposed to follow up on the threat instantly.

[Diagram]

Executing the threat immediately (W4 @ black+circle)

Dieter: Let's see what happens if Black plays there immediately.

[Diagram]

Black wins the capturing race.

Black wins this capturing race, but it seems the corner is considerably smaller now. However, there are other options too.

[Diagram]

Var

White can also play this way, but in this case, loads of aji remain and Black can still start the ko at a.

So it seems like Black started the ko immediately, to give White no opportunity to reduce the upper left.

Would that be correct?


This is a copy of the living page "Ko Fight Example From A Pro Game 4" at Sensei's Library.
(OC) 2012 the Authors, published under the OpenContent License V1.0.
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