Why is this two extension a big place to play?

Kirby · #1

So I'm reading a little bit from that book, "Invincible", and one of the game excerpts is listed below:

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . W . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The marked move, above, is said to be the last big place, but I don't understand why. It is not only this diagram. In general, I have seen pro games where early on, one of the players plays between:

Click Here To Show Diagram Code: [go]$$ $$ . . . . . . . . . . . | $$ . . . . . . . X . . . | $$ . , . . . . . , . . . | $$ . . O . . W . X . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ ------------------------[/go]

vs.

Click Here To Show Diagram Code: [go]$$ $$ . . . . . . . . . . . | $$ . . . . . . . X . . . | $$ . , . . . . . , . . . | $$ . . O . B . . X . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ ------------------------[/go]

Sometimes it's slightly different in the corner:

Click Here To Show Diagram Code: [go]$$ $$ . . . . . . . . . . . | $$ . . . . . . . . X. . | $$ . , . . . . . , . . . | $$ . . O . . W . X . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ ------------------------[/go]

vs.

Click Here To Show Diagram Code: [go]$$ $$ . . . . . . . . . . . | $$ . . . . . . . . X . . | $$ . , . . . . . , . . . | $$ . . O . B . . X . . . | $$ . . . . . . . . . . . | $$ . . . . . . . . . . . | $$ ------------------------[/go]

In any case, it's usually a two space extension alongside an enclosed corner. See the pattern?

Anyway, I don't understand it when I see this move played so early in the game. Is it really that big? Sure, the difference between white and black playing there is complementary, but for example, in the game above, it *feels* to me like so many other areas are bigger.

For example:

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . W . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

or maybe

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . W , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

or maybe even

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . W . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

or if you really want to give aid to the bottom, maybe this:

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X W . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

All of these alternative moves *feel* more active to me, and I can only trust a pro's intuition that the two space extension is actually bigger.

What's wrong with my intuition? Why is this type of move so big?

Unusedname · #2

My thoughts is

It stops black 1.
1 would be a good invasion for black because it turns 3 into a dual purpose move. surrounding the corner and providing a base.

also if black jumps out at a now white is behind enemy sector lines

or b threatens the white stones and threatens to build a framework with c

Although I also feel like this move might be a better way to help the bottom

Phoenix · #3

I think the answer is simpler.

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . 3 . . . O . 1 . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The double pincer would clearly be bad for White. Ergo:

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . B . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . 2 . . . O . 1 . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Now Black gets :b1:

in sente and consolidates territory. Which is all well and good, except :w2:

does the same in response. Of course :b1:

remains an aim for Black to take at the end of the fuseki. But first things first...

Click Here To Show Diagram Code: [go]$$ $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . W . . 1 . . . W . a b . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

This simple pincer puts both White's stones in danger. If White doesn't manage to handle his corner in sente, Black will have an ideal extension/threat at a. There's no reason to leave this option open to your opponent, so White makes the two-space extension to b in Kirby's original diagram. Now :b1:

becomes an overplay.

It's fairly typical of pro play and I'm starting to play these kinds of moves myself (with mixed results). It's important not to leave weaknesses you can't handle well before you can be proactive, especially when both players can read wide and deep. Just take territory while defending, and leave your opponent to handle your now strong position. ;-)

EdLee · #4

Kirby, here's just my idea, I dunno whether it's correct, you can see if it makes any sense.

It seems the last double sente move on the board:
After :w1:

, W(a) becomes much more severe:

Click Here To Show Diagram Code: [go]$$W $$ ----------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . a . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . 1 . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Conversely, :b1:

not only takes cash for B, but it helps (a), and threatens :wt:

all at once:

Click Here To Show Diagram Code: [go]$$B $$ ----------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . a . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . O . . . . . . Q . 1 . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ----------------------------------------[/go]

The other candidate moves don't seem to be double sente:
Gote for B to fix with :b1:

:

Maybe gote for W to kick with :wc:

:

Gote for B to fix with :b1:

:

Could be gote for W to lean with :wc:

:

Kirby · #5

Thanks for the comments thus far. One thing to note - as I read on in the commentary, the option of kicking in the bottom left was suggested as a valid alternative.

Still, I think my question remains, and the answers given thus far have been pretty good.

Thanks.

EdLee · #6

Kirby, a bit more, just for fun

Uberdude · #7

Interesting question Kirby. I seem to recall Bill saying that in general Go Seigen thought these kind of extensions were particularly big. Something to note is that if white gets that extension then black's corner is weakened a bit: if white later ends up living in the corner giving black a wall then the extension means black can't extend from his wall and may even need to worry about eyespace.

The position you posted is a rather complicated one, so instead I will consider this simpler position that came up in an OGS game of mine (I'm white) and I studied what pros did a bit:

Click Here To Show Diagram Code: [go]$$Bcm5 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . b . . . . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . c . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . 7 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . 3 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . 1 . . | $$ | . 5 . O . 4 . . . , . . . . . , . . . | $$ | . . 6 . . . . . . . 2 . . a . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The question now is do we play a (20 pro games), or a move on the top side such as approach at b (10 games), or approach on the right at c (6 games)? As you can see a is the most popular, but all of these choices black has a high winning percentage :-?

. If we don't play it, then black's extension there is likely sente (Otaka and Kobayashi played this way):

Click Here To Show Diagram Code: [go]$$Wcm12 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . 3 . . . | $$ | . . . . . . . . . . 5 . . 1 . . 4 . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . 2 . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . 7 . . . . . X . . | $$ | . X . O . O . . . , . . . . . , . . . | $$ | . . O . . . . . . . O . 6 . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

If we do get it, then later we can aim at moves such as a to both grow our own lower side moyo and reduce a black one on the right (black can also aim at the same point or one to the left), though the shoulder hit at b remains as a nice point for black to reduce, or the c-f sequence on the left.

Click Here To Show Diagram Code: [go]$$Wcm12 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . d c . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X e . . . . . . . . . . . . . . . | $$ | . . f . . . . . . . . . . . a . X . . | $$ | . X . O . O . . . b . . . . . , . . . | $$ | . . O . . . . . . . O . . 1 . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

My opponent answered my 2 space extension with the big point on the right side which in terms of "bigness of gap" does look bigger, but strangely enough no pros played this way, they all played on the top side, mostly approaching at a. I'm not really sure what to make of this. The game, which is still going, is rather close and I am not confident of winning which is a bit disappointing for me as previously I beat this opponent fairly comfortably. He made a big right side, and despite me spending a move on the lower side I didn't get a lot of points there. Maybe I just played too simply and didn't give him enough opportunities to make mistakes. Then again if I win by half a point I shouldn't complain too much.

Click Here To Show Diagram Code: [go]$$Wcm12 Amateur game continuation $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . a . . . . . . . 3 . . . . . | $$ | . . . O . . . . . 5 . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . 6 . . . . . . . . . . . . 4 . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . 2 . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . X . . | $$ | . X . O . O . . . . . . . . . , . . . | $$ | . . O . . . . . . . O . . 1 . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

I'm not sure what conclusions to draw from my game, and the low white winning percentage in pro games, but I think next time this fuseki comes up I will try a different move and see how it goes. Or as it seems difficult to make territory on the lower side, I might play this way for thickness earlier on:

Click Here To Show Diagram Code: [go]$$Bcm5 $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . O . . . . . , . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . . . , . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . 6 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . 3 . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . 1 . . | $$ | . 5 . O . 4 . . . , . . . . . , . . . | $$ | . . . . . . . . . . 2 . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Bill Spight · #8

Uberdude wrote:

Interesting question Kirby. I seem to recall Bill saying that in general Go Seigen thought these kind of extensions were particularly big.

Gee, I don't recall that.

But yes, the extension is a big place and, indeed, the last big place of the opening.

That is not the same as saying that it is the best play. Remember the proverb, urgent plays before big plays. Big place is a technical term. An invasion is not a big place, a wedge on the side is. In a particular case, an invasion may be more urgent than a wedge, and thus bigger in the sense that you are talking about. But the wedge is still a big place, the invasion is not. Extensions on the side are also big places, and this was the last one.

I agree that it does not look that big. It is a play that I had to come to appreciate, just as I had to come to appreciate thickness and honte. As Uberdude pointed out in reply to a question by PeterPeter, you have to look at the future developments from a play to assess its worth.

Now, I knew that pros made these extensions, but I found it hard to make them myself. They look so small. I gradually began to make them, as a last resort. As I tried them out, I began to appreciate them more and more. By now this one looks obvious to me.

Just one comment on this particular diagram. I don't know if anybody else has already mentioned it. Suppose that it was Black's turn, and Black invaded the bottom side just left of the single White stone. One problem with that invasion is that White can make the two space extension to the right. A Black extension from the bottom right corner would prepare an invasion. White's extension not only prevents that Black extension, it prepares to pincer any Black invasion on the bottom side.

ez4u · #9

We should be careful of how much we make out of the original question. If we plug the bottom of the board into kombilo as shown below, we come up with exactly one hit - the game in question with its extension to "a".

Click Here To Show Diagram Code: [go]$$B Continuations $$ $$| . . . . . . . . . . . . . . . . . . . | $$| . . O . . . . . . . . . . . . . . . . | $$| . . . . . . . . . . . . . . . . . . . | $$| . . . . . . . . . . . . . . . . . . . | $$| . . X . . . . . . . . . . . . X . . . | $$| . . . , . . . . . , . . . . . , . . . | $$| . . . O . . . . . . O . . a . X . . . | $$| . . . . . . . . . . . . . . . . . . . | $$| . . . . . . . . . . . . . . . . . . . | $$+ - - - - - - - - - - - - - - - - - - - +[/go]

If instead we shorten the search space to exclude the pincer stone we get 24 matches

Click Here To Show Diagram Code: [go]$$B Continuations $$ $$| . . g b . . . . . . . . . . . . . . . | $$| . . . . . . . . . . . . . . . . . . . | $$| . . X . . . . . . . . . . . . X . . . | $$| . . . , a c f . . e . . . . . , . . . | $$| . . . O . . . . . . O . . d . X . . . | $$| . . . . . . . . . . . . . . . . . . . | $$| . . . . . . . . . . . . . . . . . . . | $$+ - - - - - - - - - - - - - - - - - - - +[/go]

Code:

24 matches
Wa:    12 
Wb:    5 
Wc:    3 
Wd:    1 
Be:    1 
Wf:    1 
Wg:    1 

Here the one example of White extending to "d" is again the game in question. Half the time White plays the diagonal move at "a" instead. Another 3 times White chooses the knight's move at "c".

So why does White choose the 2-space extension at "d" in the game? I think it is because of the White pincer and the supporting White stones behind it. Normally if White played two (or three) low stones on the lower side, Black would naturally press down the White 3-4 stone. However, in this case if Black presses as below, there is not follow up move. White is too strong on the left side for Black to invade. So this situation is unusual in that the Black stone in the lower left has no useful role to play and White can pretty much ignore it when deciding to make the two-space extension. (Also note that Shusaku lost this game so maybe the extension wasn't the best choice, YMMV. :blackeye:

)

Click Here To Show Diagram Code: [go]$$Wc If Black Presses... $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , 2 4 . . . , . . . . . , . . . | $$ | . . . O 3 . 5 . . . O . . 1 . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Uberdude · **#10**

ez4u wrote:

However, in this case if Black presses as below, there is not follow up move.

That's true, but also white is low. Maybe white would push and cut? Or does that just give black momentum to make shape?

But continuing as below black makes decent shape too and white feels overconcentrated...

Click Here To Show Diagram Code: [go]$$Bc If Black Presses... $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , X X 5 . . , . . . . . , . . . | $$ | . . 9 O O 1 O 6 . . O . . O . X . . . | $$ | . . . 0 7 2 3 4 . . . . . . . . . . . | $$ | . . . . . . 8 . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Bill Spight · **#11**

Just to be clear, when I said that the extension was obvious, I did not mean that it was obviously the best play, just that it was obviously a good play, and bigger than it looks.

In fact, my first thought was the kosumi in the bottom left corner ("a" in the next diagram).

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , a . . . . , . . . . . , . . . | $$ | . . . O . . . . . . O . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

It seems to me that the pincer on the left side, indeed, White's strength there, is a big factor.

Click Here To Show Diagram Code: [go]$$Wc If Black Presses... $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . O . . . . . . . O . . O . . . | $$ | . . X , . . . . X , . . . . . , . . . | $$ | . . . X . . . . . . . . . . . . X . . | $$ | . . O X . X . . . . . . . . . . . . . | $$ | . . O O X X O . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . . O X . . . . . . . . . . . . . | $$ | . . . , O . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . O . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . , 2 4 . . . , . . . . . , . . . | $$ | . . . O 3 a 5 . . . O . . 1 . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

A couple of thoughts on this sequence. First, I would play :w5:

at "a", to be stronger in the corner. I would not be particularly concerned with getting ahead of Black, because I already have a base after :w1:

. (This would avoid the sequence Uberdude shows.

) Second, instead of :w3:

I would be inclined to push and cut. A difficult fight would ensue, but with the White strength on the left side and the base on the bottom side, I am prepared for it.

ez4u · **#12**

Uberdude wrote:

ez4u wrote:

However, in this case if Black presses as below, there is not follow up move.

That's true, but also white is low. Maybe white would push and cut? Or does that just give black momentum to make shape?...

I didn't give it enough thought. I think pushing and cutting is much more interesting. Alternatively, if White gives way, don't jump immediately in order to avoid giving Black easy forcing moves. I think that White's original extension signals a willingness to let Black live small in the lower left or the bottom side (giving up the lower left approach stone in exchange).

I think the main point remains that the decision to extend in front of the shimari in this game is related to the diminished prospects of the lower left approach stone. In the more general case, where that stone retains more potential, it is more urgent for White to play in the lower left.

Why is this two extension a big place to play?

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