Beginner Exercise 86 / Solution

Sub-page of BeginnerExercise86

B3 is the correct way to attack.


W4 and B5 is the best play for both players, with White taking the ko first.

Refer to Tripod Group with Extra Leg for more details.


A ko to win  

Paul Pogonyshev: this move looks fine. It threatens the white+square stones.

lavalyn: Not really. See below.

Paul Pogonyshev: Yes, it's not as fine as it looked :)

White captures  

If White captures, Black responds with B5.

White must capture again  

If White doesn't capture again, she loses white+square and the second eye. So she has to play at W6. Black threatens with B7. White has no option other than to connect with W8 and then Black captures ko with B9, forcing White to connect with W10. It's over now: Black places a stone at a, killing White.

White 8  

unkx80: W4 in the above dagram is OK; but W8 should simply capture a stone in the corner and make two eyes at W10.

Of course, lavalyn's alternative way of playing W4 (shown below) is correct too.

lavalyn claims the solution above fails:

A ko to win - failure  

Delaying the capture but preventing Black from playing in the corner - no suicide allowed.

A ko to win - success  

The exchange of B3 for W4 is necessary to reduce White's liberties. Now when the ko is played at B5, White must take - unlike the previous diagram.

Paul Pogonyshev: it's night time and I am tired, but as far as I can see, White is alive with three eyes here. What's wrong?

lavalyn: W4 and the white+circle stones are in atari. But if White fills against the atari, Black takes the corner - the resulting three-space big eye is dead.

A ko to win - success?  

Paul Pogonyshev: This is what I believe is on the board after the sixth move. Black can't capture at a (ko). Next move White captures at b, or if Black has played there, at c and lives with three eyes. Or not?

unkx80: Please see Ko fight Example on what goes on during a ko.

Paul Pogonyshev: OK, I knew what ko is ;) I merely misunderstood the task, thinking it was to kill White.

A ko to win - alternate  

This looks like it also works for ko. However, since White captures first in the previous diagram, White will prefer playing W4 next after B3 (try to get first capture in a ko).

For more information, reference the Tripod Group with Extra Leg.

Beginner Exercise 86 / Solution last edited by Unkx80 on November 3, 2005 - 12:23
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