Forum for J group
why ever make the J-group? [#1704]
![[Diagram]](diagrams/4/d56f6d1505c5eb8f43909f4454ca0957.png)
![[Diagram]](diagrams/41/55ee5afef437cb1c43e2a916a2ea2372.png)
Hmmm, well, why does anyone ever make a bad move? :-)
Most people that make the J-Group do so because they don't know that it is dead, or don't know that they can get ko with the straight J-group. Or they make it in a situation where the straight J group is not available, eg:
![[Diagram]](diagrams/29/f23981a97002c842045057460ff59f0a.png)
If the J-group lives or dies according to sente, but the straight-J with
at a can only be killed with ko, why ever make a J-group? Why not always decend to make the straight J?
By and large, I agree with you. But this is only after we know the results for the J-group. The proof of this "theorem" is nontrivial and requires some requisite knowledge to understand.
By the way, the J-group with hane is also known to be alive. This result is used in the 4-4 point double kakari tenuki joseki, see joseki-related life-and-death example 4.
![[Diagram]](diagrams/24/4cf9db62589e9940852a2884fc9f454d.png)
![[Diagram]](diagrams/22/111956fc90672e36f3874f6257fea947.png)
? He must be afraid of this 
for some reason, if it makes sense to play a instead of If the attacker plays first, basic J-group without hane means death, while basic J-group with hane means unconditional life.
The straight J-group with hane deserves its own section. If I am not wrong, Black stands to lose two stones to ensure unconditional life.
I think Black can kill straight-J unconditionally.
![[Diagram]](diagrams/42/2fcac841238fd82fd250f8b3e87d7c30.png)
![[Diagram]](diagrams/25/63648ee2d8f94dd52928a37ec5414d72.png)
![[Diagram]](diagrams/17/75b5ef374ee92684144513fe4244ad77.png)
![[Welcome to Sensei's Library!]](images/stone-hello.png "Sensei's Library")