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LifeAndDeath

 

JGroups
Path: LifeAndDeath   · Prev: TripodGroup   · Next: CombFormation
  Difficulty: Beginner   Keywords: Life & Death

[Diagram]
Diag.: J-group

The black shape in the diagram is the basic J-group. It has the same status as an L+1 group (see The L Group is Dead): it lives or dies according to sente.


[Diagram]
Diag.: White kills

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, followed by a placement on the vital point, followed by a descent and a throw-in. The best way for Black to live is by playing at 3, giving him 6 points of territory. The order of 1 and 3 is reversible.


[Diagram]
Diag.: 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.


[Diagram]
Diag.: ko 1 - White captures first

Here is her best sequence to produce the ko. White gets to make the first capture.


[Diagram]
Diag.: ko 2 - Black captures first

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.









--Stefan



[Diagram]
Diag.: Black 4 has an alternative

However, I would like to add to the discussion by adding this diagram. Black can play at 4, aiming to escape at 'a'.


[Diagram]
Diag.: It's a ko!

White has to respond at 1 (if white responds at 3 instead, black can start a ko at 'a'), and the result is a ko.


[Diagram]
Diag.: J-group

However, this version of the J-group is definitely dead after 1, 3 and 5. There is no chance for a ko.









--unkx80



[Diagram]
Diag.: Black 4 has an alternative in special cases

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 The L Group is Dead. 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) W 5 finishes off B. 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!

--DaveSigaty

That's why I try to teach fellow beginners the merit of a net above a ladder. The ladder is a NonLocalMoveVersusALocalMove: 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



Practical application

[Diagram]
Diag.: Not recommended!

Black should under almost no circumstances ignore the double kakari and let White play 1. But how does Black continue if he decides that he has to play this line after all?


[Diagram]
Diag.: J-group

Black retreats to san-san and White tries to keep his eyespace as small as possible.


[Diagram]
Diag.: Kikashi before living

Black plays the kikashi of 1 and 3 before living in the corner, in accordance with the proverb.



--Stefan



Path: LifeAndDeath   · Prev: TripodGroup   · Next: CombFormation
This is a copy of the living page "JGroups" at Sensei's Library.
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