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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 who has sente. This basic shape is known in China as the Big Pig's Snout.
The correct way for White to kill this shape looks like a complete display of the principal killing techniques: reducing the eye space with a hane at , followed by a placement on the vital point at , followed by a descent at and a throw-in at . The order of and is interchangeable.
The best way for Black to live is by playing at , giving him six points of territory.
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 , aiming to escape at b.
White has to respond at (if White responds at instead, Black can start a ko at a), and the result is a ko.
The J group with an extra hane
For example, if White plays and , Black lives with and . Other details are left for the pleasure of the reader.
Other moves than work too. But Black should not play to the left of - Black dies in a similar way to the J group without hane. -Han
White can make an endgame gain with the given sequence. -Han
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 (though White also has the option to unconditionally snip off the two lower black stones leaving the main Black group alive, which might be better in rare cases).
There are several good ways to produce a ko and one less good way. A representative good variation is shown. 1 can be at a, or with 1 as shown, 3 can be at 5 or a, each giving a more-or-less equally good result with White getting to make the first ko capture.
This way of setting up a ko is less good. It only works when the black group has no external liberties and Black gets to make the first ko capture (though if White wins the ko, she removes a part of the black group from the board).
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 this way. He sacrifices two stones and plays at .
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, instead of a keeps Black short of liberties. Black can't play at b now and must play for the ko.
All 'good' variations of the first ko from the previous section still work with the extra outside liberty.
Straight J group with an extra hane
If White plays first, the status of the Black group depends on the number of outside liberties.
Like the straight J group without extra hane, kills the Black group in a ko when Black has no outside liberties.
The straight J group with extra hane is unconditionally alive when Black has a outside liberty. However, White can capture two Black stones via the sequence from to .
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) finishes off Black. In studying life and death, then, we need to learn the basic techniques. Next, memorization of the fundamental cases can be a powerful tool to improve play in real games.
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.
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.
Andy: If the Straight J group is more robust than the Basic J group, because the Straight J is ko if the opponent plays first while the Basic J is dead if the opponent plays first, why ever make the Basic J group? Are there advantages the Basic J has over the Straight J, and could those be explicitly listed on this page please?
fw280?: We make J group instead of straight J, when we have hane. Because J group with hane is better than straight J.
- Joseki-related life-and-death example 4
- Joseki-related life-and-death example 9
- JGroup application 1