The position after comes from the game, GoGoD 1787-06-26a, between Honinbo Retsugen, 6 dan (W) and Yasui Senchi Senkaku, 5 dan.

Click Here To Show Diagram Code

[go]$$Wcm8 Moves 8 to 12, Comedy of errors
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X . . . . |
$$ | . . . , O . . . . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 7 . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . 4 6 . . . . . . . . . . . . |
$$ | . . . X . 2 3 . . . . . . . . . O . . |
$$ | . . X , . 1 . . . , . . . . . , . . . |
$$ | . . . . O . . . 5 . . . . . . a . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Elf, assuming komi, OC, says that loses 14% to par, and then returns the favor, losing 14½% to par. and are fine, but then loses 16½%. Finally, loses a whopping 23½% to par!

I confess that, seeing this joseki any number of times in old games, I had my doubts about , but looked good to me. And apparently fell out of favor because the result through looked too good for Black to top players in the 19th century, as well. Elf, however, reckons that the sequence, - , loses 21%.

is a borderline error, losing 5½%. It is thin, OC, but it does counter Black's thickness. Elf prefers to enclose the bottom right corner.

Click Here To Show Diagram Code

[go]$$Wcm14 Variation for
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 3 . . . . . . . . . . . X . . . . |
$$ | . . 2 , O . . 5 . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 4 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . X X . . . . . . 8 . 6 . . . |
$$ | . . . X . X O . . . . . . . . 7 O . . |
$$ | . . X , . O . . . , . . . . . , . . . |
$$ | . . . . O . . . O . . . . . . 1 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

After , Black's play is interesting. could also be at 16, OC, but we may consider as a probe. After White replies at , plays a long extension from his thickness. Takagawa explains this kind of tenuki by saying that Black has prevented an ideal play for White (the usual enclosure) with sente, and can be satisfied with that. is the Go Seigen/AlphaGo shoulder hit. The light jump, , is a shallow reduction of White's bottom side framework.

Top choice: Invade the bottom right corner

Click Here To Show Diagram Code

[go]$$Bcm13 3-3 invasion
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X . . . . |
$$ | . . . , O . . . . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . b . . |
$$ | . . . . . X . . . . . . . . 9 8 a . . |
$$ | . . . X . X O . . . . . . . 4 7 O . . |
$$ | . . X , . O . . . , . . . . 2 3 . . . |
$$ | . . . . O . . . O . . . . 6 5 . 1 . . |
$$ | . . . . . . . . . . . . . . 0 . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

The 3-3 invasion against the 5-3 is obviously a good play, now that the bots like it. stands to block Black out of the bottom side. cuts high. If Black cuts at a he suffers the atari at b.

Click Here To Show Diagram Code

[go]$$Bcm23 Mainline, continued
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X . . . . |
$$ | . . . , O . . . . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . 0 . . . |
$$ | . . . . . . . . . . . . . . . 8 9 . . |
$$ | . . . . . . . . . . . . . . . 6 7 . . |
$$ | . . . . . . . . . . . . . . . 4 5 . . |
$$ | . . . . . X . . . . . . . . X O 3 . . |
$$ | . . . X . X O . . . . . . . O X O . . |
$$ | . . X , . O . . . , . . . 2 O X . . . |
$$ | . . . . O . . . O . . . . O X 1 X . . |
$$ | . . . . . . . . . . . . . . O . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

connects, and eliminates a cutting point. is atari. White builds a strong wall while Black makes territory on the 3d line. A few years ago I would have considered this lengthy exchange to be good for White. Each push by Black gains about 2 pts. of territory, while I figured that each extension on the 4th line gains on average more than 3 pts. In addition there is the proverb about not pushing the cart from behind. Live and learn.

Click Here To Show Diagram Code

[go]$$Bcm33 Mainline, continued again
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X . . . . |
$$ | . . 4 , O . . . . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . 2 . . . |
$$ | . . . , . . . . . , . . . . . O 1 . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . X 3 . . . . . . . X O X . . |
$$ | . . . X . X O . . . . . . . O X O . . |
$$ | . . X , . O . . . , . . . O O X . . . |
$$ | . . . . O . . . O . . . . O X X X . . |
$$ | . . . . . . . . . . . . . . O . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

pushes once more, and now the turn is good for . encloses the top left corner.

Again, long variations should be taken with a grain of salt.

OC, invading the bottom right corner is a good play, but what is wrong with ? I confess I don't know. And that's really why I chose this problem. Usually the center turn shape with three stones is good, and this series has shown examples where it is good, whether the result of a turn or of a solid connection. This is an important exception to the rule. I can see how the 3-3 invasion might be preferable, but the difference of more than 20% is quite a shock! Food for thought.

Opening gospel says: upper left corner is biggest, unless there's an urgent move on the lower left.

Click Here To Show Diagram Code

[go]$$Bcm13 Black to play.
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . 6 . . . . . . . . . . . . . . . . . |
$$ | . 3 2 4 . . . . . . . . . . X . . . . |
$$ | . 7 1 , O . . . . , . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 5 . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . X . . . . . . . . . . . . . |
$$ | . . . X . X O . . . . . . . . . O . . |
$$ | . . X , 0 O . . . , . . . . . , . . . |
$$ | . . . 9 O . . . O . . . . . . 8 . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

My first 10 moves.
The - exchange might be a case of sente but if Black would play it before the upper left, then White can safely ignore, I think.

3 3 it is

Hmm, the 3-3 was obvious by now.

More interesting is why B's sequence is considered so bad.

Presumably the point is that all W needs to live on the left is a 3rd line stone, after which the centre isn't doing much.

So W lived on the lower side in sente, and B has no territory yet, and must look for a return in the centre, for which there isn't anything yet.

It isn't clear to me why 12 is so bad, but I presume that it is too close to strength.