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June 1998's Go Answer of the Month

Dia A1, B1 & C1 - Status?

Dia A1   Dia B1   Dia C1

Three seki related status questions. For each diagram what is the status - settled or unsettled; live, dead or seki? Use of Richard Hunter's '6 types of fights' liberty counting may be relevant, see the Liberty Counting Table.

Individually, none of the three should be too hard. I have posed three diagrams to provide variations on a theme.
In diagram B1, White has just played. Black may of course choose to pass.

Existing literature tends to use 'shared' or 'mutual' as adjectives when discussing sekis.
Richard Hunter dislikes these because the liberties are not shared, they are allocated according to the type of fight, and those adjectives can be misleading. He prefers 'inside'.
'Inside' is fine for No eye Versus No eye fights, but itself becomes confusing when either party has a eye. There is then a tendency to consider the eyespace as the inside liberties. I have suggested 'border', but this also has its opponents. I'll stick with inside for the moment.

To start with Dia A1. This was a shape I discussed with Richard Hunter last year. Although he said he might use it in his series of articles, I was surprised to see it appear in BGJ 111 after posting this problem. Anyway - you get my answer here, read BGJ 111 for Richard Hunter's answer.

Dia A1 again.

Dia A1 again

Maybe ... Working down the table of fight types in the Liberty Counting Table it looks like a No Eye v No Eye (2 or more inside liberties) type 2 fight.
So the favourite is the one with more exclusive liberties - Black (6) to White (4).
So Black gets One inside liberty and White gets All inside liberties. So Black = 6+1 = 7 and White = 4+4 = 8.
Therefore it is settled, White winning. So White has no need to play and Black achieves nothing by playing. ... or maybe not.

Dia A2 A potential eye!

Dia A2

More careful study reveals that triangle is not a true inside liberty. It is solely adjacent to Black stones. At this point you have two different approaches to analysing the situation:

  1. No eye v. No eye. Type 2. Black (6+1) is favourite (White 4). Black = 6+1+1 = 8, White = 4+3 = 7. It is settled, Black wins.
  2. If it becomes a Type 3 Eye v. No eye fight, Black will get all the inside liberties. White doesn't want that and so plays to the right of triangle to remove the eye. That leaves it as a type two fight, Black = favourite = 6+1 = 7, White = underdog = 4+3 = 7. Unsettled, but it is Black's turn to play. So Black wins.

The status is: Black wins.

Dia B1 again.

Dia B1

Dia B1 is from a question posed by Matthew Macfadyen. The answer to his question is to show that an agressive Black gets killed by good white play. We investigate the more subdued and sensible Black moves here.

Dia B2 & B3 - Aggressive (and poor) Black play.

Dia B2   Dia B3

In Dia B2 after White 7, Black is in a fix. If he links under with 8', White captures 4 with 9' and then a Black 10' linking 6 to 2 is out of liberties.
Thus White gets two eyes (at 4 and 6).

In Dia B3, White gets two eyes directly.

Either way White lives with territory. Therefore the Black would prefer to play for a seki the corner.

Dia B4 - Seki.

Dia B4

The biggest nakade that Black can build in the corner is the gun shape. When that is done, there will be two 'inside' liberties left. So Black cannot kill White by reducing him to one eye.

Seki analysis: No eye v. No eye, 4 inside liberties, Type 2. White is favourite. White = 1+1 = 2, Black = 0+4 = 4. Black can force a seki.

Back in Dia B1, if it was White's turn to play, he can play as Dia B2 (with Black 2 omitted) and gets life with territory.

The status is: Black can get a seki, White can live with territory.
It is a gote seki for Black, and a gote white play for about 8 points. Thus both players are likely to leave the situation for a while, playing bigger moves elsewhere first.

Dia C1 again.

Dia C1

This is a standard book situation. If you don't know it, you may be wondering where the problem is. It is assumed that the white group is live and that the seki (if any) is between the black stones and white ones yet to be played.

If Black plays first, he can get life with territory.

Dia C2 - White gets a sente seki.

Dia C2

Starting at the 3-2 point is correct. White can also get a seki by playing 1' at 2 here, but that is gote.

For more details, see page 88 of All about Life and Death (Vol 1) - Cho Chikun.

The status is: Black can get gote territory (7 points), White can manage a sente seki.

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