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Square Nine in the Corner
Path: LifeAndDeath   · Prev: GunEight   · Next: SixDieButEightLive
Path: SecondCourseOnKo   · Prev: SolutionToJfc001   · Next: KarlKnechtelSKoStory

    Keywords: Life & Death, Ko

Square nine in the corner is related to the carpenter's square.

1. No outside liberties

[Diagram]
Diag.: Square nine

When there are no outside liberties, White can turn this into sente seki [1]. The vital point (obviously) is a.


[Diagram]
Diag.: Main line

The points 2 and 3 are miai. Black 6 avoids White starting a Ten Thousand Year Ko at a.

KarlKnechtel: Coincidentally, I was studying this eye space earlier today with a friend on LGS...



[Diagram]
Diag.: KK contributes this variation at 6

This way avoids the ten thousand year ko as well. Note that Black cannot resist White's attempt later by filling the ko in response to the approach:


[Diagram]
Diag.: Oops! (Black 6 tenuki)

Now Black's eye space is almost filled with a bulky five, and Black dies.



[Diagram]
Diag.: Variation at 5

This becomes seki too, but if Black omits 6, the ko started at 6 is slightly more advantageous for Black in that he can capture first.


[Diagram]
Diag.: Variation at 4

Black 4 here is not so good, as it invites a two stage ko.



[Diagram]
Diag.: Variation at 3

This variation also becomes seki, but White ends in gote.


[Diagram]
Diag.: Variation at 3 (ii)

Black trying to avoid seki by taking away the eye is not a good idea because it becomes seki anyway and Black takes gote too.



2. One outside liberty

[Diagram]
Diag.: Main line

With one outside liberty the same main line applies, except that White must play gote at 7 to make it seki.



3. Two or more outside liberties

[Diagram]
Diag.: Main line

With two or more outside liberties, the attempt to make seki fails. White 1-7 can better be held in reserve as ko-threats.



[1] Bill: This position is hyperactive, depending on who is komaster. If Black is, or if neither player has any ko threats, White can make seki in gote.

[Diagram]
Diag.: Gote seki

Think about it. What does White threaten?


[Diagram]
Diag.: Seki variation I

White can try 1, but Black 2 takes away the eye. Now what?


[Diagram]
Diag.: Seki variation II

This leads to a 10,000 year ko, which White will be reluctant to start. Or White can play at a to preserve the seki.

[Diagram]
Diag.: White as komaster: the threat

When White is komaster, things are trickier. White threatens W 1 - 5. Now there is a 10,000 year ko that favors White. Unless Black can become komaster, he should often go ahead and bite the bullet with Black 6. Since he will lose the ko, the earlier he does so, the larger are the plays he gets in exchange.

By the same logic, Black should normally reply to White's invasion, setting up a ko to lose while there is still time.

[Diagram]
Diag.: Black makes ko to lose it now.

Black 7, 9, 11 elsewhere.

After White starts with the marked stone, Black gets three plays elsewhere in exchange for the corner. The right time to do this is when the miai value of these plays is around 7 points.

When he cannot get so much in return for the ko, Black should usually make seki in gote, as shown in the Main Line diagram.



Path: LifeAndDeath   · Prev: GunEight   · Next: SixDieButEightLive
Path: SecondCourseOnKo   · Prev: SolutionToJfc001   · Next: KarlKnechtelSKoStory

This is a copy of the living page "Square Nine in the Corner" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.