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J groups
Path: LifeAndDeath · Prev: TripodGroup · Next: BentFourInTheCorner
Difficulty: Beginner
Keywords: Life & Death
Basic J group
The black shape in the diagram is the basic J group. It has the same status as an L+1 group: it lives or dies according to sente.
The correct way for White to kill this shape looks like a complete display of the principal killing techniques: reducing the eye shape with a hane at The escape with one missing white stone
There is one caveat to the above discussion on the J group though. Without a white stone at a, Black can play at
White has to respond at
However, with
This version of the J group is definitely dead after The J group with an extra hane
With the marked hane, Black is alive. There is no ko.
For example, if White plays [4] Straight J group
Black can improve on the status of his corner by descending to the edge instead of making a hanging connection. The best White can do now is turn the corner to ko.
Here is her best sequence to produce the ko. White gets to make the first capture.
Here is another way to set up a ko, but this one only works when the black group has no external liberties. Black gets to make the first capture, but if White wins the ko, she removes a part of the black group from the board. The straight J group with an outside liberty
If Black has an outside liberty, the second ko doesn't work because he can live by answering
Black is alive in sente for an average gote endgame by white. This result is very favourable for black over being killed straight. If Black had expected 6 points in the corner - he needed to defend the two stones and against the hane - he now has 4 points (B = -2). White on the other hand made 4 points by the two-stone capture (W = +2). As a net loss of six points (B = -2 -4), Black gains hugely in this exchange for not playing gote twice. White might think in terms of "I made 6 points", but she has to realize that she lost around 13 (approx. 19 for capturing the group minus 6 points) points by starting with the wrong move.
When there is no extra outside liberty, as here,
The first ko still works with the extra outside liberty. Practical application
Black should under almost no circumstances ignore the double kakari and let White play
Black retreats to san-san and White tries to keep his eyespace as small as possible.
Black plays the kikashi of Discussion
Life and death evaluation of shapes is normally done without the ability to escape. Look at the funny white 'wings' on the outside of the L-group in the first diagram of L Group. Even the L-group is alive in sente if descending to either edge is a threat to escape.
The present shape would normally be studied/evaluated with a white stone at b to prevent such an escape. In such a case (no escape) However, as much as the vital points and main continuations, we need to thoroughly understand the various conditions such as no escape, no/limited outside liberties, relationship to the corner, etc. that may apply to each case. Small differences in game situations can turn around any of the proverbs/rules of thumb that we have studied so hard! That's why I try to teach fellow beginners the merit of a net above a ladder. The ladder is a non-local move versus a local move: you need to look at more parts of the goban. Ladders may be easier to pattern-match; sure - but a ladder's status changes more rapidly than a net's. --JanDeWit I totally agree with DaveSigaty and JanDeWit on their views. Actually, I have wanted to add the part provided by DaveSigaty after I made the changes but I was unable to get onto this site then. --unkx80 See also conventions in life and death. ContributorsPath: LifeAndDeath · Prev: TripodGroup · Next: BentFourInTheCorner This is a copy of the living page "J groups" at Sensei's Library. ![]() |