Re: Life & Death in the middle
Posted: Thu Sep 13, 2018 5:15 am
Here's a reply I wrote before mitsun's good analysis of the local situation (though I wouldn't say atari is very good as white pretty much needs to defend afterwards as explo said, but Elf does seem to often like that position) as no one mentioned tedomari.
Joaz was wrong to say black must extend. Black could extend, it's a fine move at amateur mid-dan level or Ian's sdk (and simple if you want to avoid complicated josekis). At super-strong level I suspect it's a mistake and I can explain to myself some plausible explanations.
First, the local shape. dfan's explanation was sound: if extend white will crawl once and black is reluctant to tenuki (but I wouldn't say must answer when there are very big tenukis like empty corners available, there are some similar modern josekis where allowing the hane is considered ok) so black ends in gote and white has a solid territory without the double cut weakness of dfan's first diagram. Black has a nice wall, but the peep of the cutting point can be annoying later (the importance of this is a key point from AI), though not as annoying as with black playing the old joseki of hane after a wall of two. White would not continue crawling with 4 and so on in Joaz's last diagram (though crawling a second time against old knowledge is seen these days with the hane after wall of two variation, so never say never).
How about globally? An important plus for tenuki in the game position is there are 3 empty corners remaining. This means if play proceeds with taking them Black will get the last one: tedomari, the final large play before the value of available moves drops. If there were only 2 empty corners left (e.g Black 4-4, white 4-4, black invade) then I suspect LZ would consider extend less bad compared to tenuki because white could still get the last corner (but of course depends on orientation of wall compared to other corners, I think white would like to get the corner facing the wall but black can prevent this).
So in conclusion: tenuki and extend are both fine moves and it's good to be aware of both (plus other local choices like both hanes). When deciding if you want sente or gote think about who gets to play in the last empty corner.
Joaz was wrong to say black must extend. Black could extend, it's a fine move at amateur mid-dan level or Ian's sdk (and simple if you want to avoid complicated josekis). At super-strong level I suspect it's a mistake and I can explain to myself some plausible explanations.
First, the local shape. dfan's explanation was sound: if extend white will crawl once and black is reluctant to tenuki (but I wouldn't say must answer when there are very big tenukis like empty corners available, there are some similar modern josekis where allowing the hane is considered ok) so black ends in gote and white has a solid territory without the double cut weakness of dfan's first diagram. Black has a nice wall, but the peep of the cutting point can be annoying later (the importance of this is a key point from AI), though not as annoying as with black playing the old joseki of hane after a wall of two. White would not continue crawling with 4 and so on in Joaz's last diagram (though crawling a second time against old knowledge is seen these days with the hane after wall of two variation, so never say never).
How about globally? An important plus for tenuki in the game position is there are 3 empty corners remaining. This means if play proceeds with taking them Black will get the last one: tedomari, the final large play before the value of available moves drops. If there were only 2 empty corners left (e.g Black 4-4, white 4-4, black invade) then I suspect LZ would consider extend less bad compared to tenuki because white could still get the last corner (but of course depends on orientation of wall compared to other corners, I think white would like to get the corner facing the wall but black can prevent this).
So in conclusion: tenuki and extend are both fine moves and it's good to be aware of both (plus other local choices like both hanes). When deciding if you want sente or gote think about who gets to play in the last empty corner.