Square nine in the corner
Path: SecondCourseOnKo · Prev: Jfc001/Solution · Next: PointsOrKoThreats1AtB
Square nine in the corner is related to the carpenter's square.
JennyRadcliffe: This came up in a tournament game I was playing last week, and since I'd never seen the shape before I was bewildered. I was white, and my opponent had sente and played a, so I decided to ignore it, assume it was alive and get on with the rest of the game. Afterwards, I asked a 1kyu about it ... his answer was basically a summary of this page, but I'm fairly certain he also described it as Someone's Square. Only I can't remember the name.
IanDavis hint Think 70's cheesy music, or indeed look at the first sentence in this page.
JennyRadcliffe: Last time I looked, "related to" wasn't the same as "is" ... not that Will was necessarily right, he might have said it was the Carpenter's Square and been wrong.
Fishmongers then?
Lawrence Czlapinski: Jenny, you're right it is related to the carpenter's square. The square nine can also occur in other areas of the board.
1. No outside liberties
When there are no outside liberties, White can turn this into sente seki [1]. The vital point (obviously) is a.
LCzlapinski: The square nine? can occur in other positions on the board as well. When possible, the vital point should be taken before completing the enclosures especially by the defender.
Karl Knechtel: Coincidentally, I was studying this eye space earlier today with a friend on LGS... This way avoids the ten thousand year ko as well.
Note that in case of tenuki, Black cannot resist at (filling the ko)
Now Black's eye space is almost filled with a bulky five, and Black dies.
This becomes seki too, but if Black omits 6, the ko started at is slightly more advantageous for Black in that he can capture first (try to get first capture in a ko).
This variation also becomes seki (even an 1 zi better to White one, in chinese scoring), but White ends in gote.
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.
LCzlapinski: Actually black must play at . Otherwise white can kill. See 3 (iia) below.
LCzlapinski: Black is dead after . White would not normally have to play out the rest of the moves.
2. One outside liberty
With one outside liberty the same main line applies, except that White must play in gote at to make it seki.
3. Two or more outside liberties
With two or more outside liberties, the attempt to make seki fails. to
are better 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.
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.
When White is komaster, things are trickier. White threatens to
. 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
. 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.
,
, Black 11 elsewhere.
After White starts with , 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.
Discussions about this shape in KGS's English room on 23/6/3 suggested the name 'Peachy 9' for this shape. (As in 'Everythings peachy', and not as in 'It's all gone pear shaped'. Perhaps the following shape could be called a pear shape...)
Path: SecondCourseOnKo · Prev: Jfc001/Solution · Next: PointsOrKoThreats1AtB