4-4 point diagonal attachment, low corner enclosure
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Original discussion
In the 4-4 point diagonal attachment joseki, it is not recommended to play the 4-4 point low enclosure at . In most cases, Black should play the one space jump at a instead.
One reason is that becomes a good move, pressing Black low. Then White can look forward to the bad aji at the attachments at a and b, as well as the 3-3 invasion at c.
Another reason is that when the outside White stones are strong enough, then White can look forward to attaching at and then playing
at the 3-3 point[1]. White can look forward for reducing Black's territory or increasing White's influence, or both.
In normal situations, it's impossible for White to invade the 3-3 point directly. This sequence is the most common variation to kill the White group.
(However, White does have the choice of fighting instead of trying to live in the corner-- see 4-4 point low approach low extension tenuki, diagonal attachment, 3-3 invasion for more details.)
(5d analysis by Minue)
Correct plays(locally speaking) for black are showed in following 2 diagrams.
The intent of is to defend B's corner securely. In this diagram,
,
moves might(may?) be put off, depending on a condition of whole board situation.
Another way to play is ,which is somewhat modest. In this case, it is often seen for w to invade at 3.3 immediately.
This is the basic diagram. There are several questions to answer here:
- Is
significantly worse than a?
- How does a pincer stone at B affect the matter?
The evaluation is done using KataGo as a reference.
No pincer stone
In a symmetrical parallel all star point opening
-
is 0.2 worse than invading the corner (-0.9 vs -0.7)
- The diagonal attachment
reverts back to a 0.7 lead as opposed to the preferred move, a 3-3 invasion in the opposite corner
-
is the blue move
-
loses 0.2 with respect to a, the blue move
With a pincer stone
In case of a Black san ren sei, White's lead is 1.1 to start with. Again, 3-3 invasions of either Black corner are preferred.
An inside approach at loses 0.6 and we start at 0.5. This is our reference for the discussion.
- This time the diagonal attachment of
and White's response
are both blue moves.
-
loses 0.4 while a maintains the 0.5 score.
and
follow.
Interestingly, putting pressure on the white stones may prompt White to treat those stones lightly and approach at
. Things can become quite heated from that point onward.
With a supporting stone on the side
Suppose this time that Black has played a (suboptimal) move on the side . White's approach on the outside
will result in this sequence. Traditionally it was considered bad for Black to kick at
but nowadays, due to AI evaluation, making White stronger towards an open side is considered playable because Black gets sente.
If instead Black plays low, he'd lose about 0.7 in this position:
In this case White's stones are considered more resilient, allowing White to take sente. Both a and b are now available.
About the 5d recommendation
KataGo doesn't like all that much.
makes a base. Black can indeed gain influence towards
with
and
but this doesn't offset White's sente.
In a case of synchronicity Michael Redmond has just released this video