Question about problem 7 in Making Good Shape

Jujube · #1

At the end of the correct answer, which is about cutting across the knight's move to make shape, it says: Black A is sente.

Why is this? I was looking at the clamp or the placement on the 2,2 point but wasn't sure. What's the reason for this being sente?

EdLee · #2

Hi Jujube,

Bill Spight · #3

EdLee · #4

Hi Jujube, Bill,

Sorry, I missed:

Joaz Banbeck · #5

I like the clamp:

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

If white sacrifices the three outliers and goes for the corner, he doesn't get enough room.

Click Here To Show Diagram Code: [go]$$B $$ --------------- $$ . . 7 8 . 9 . | $$ . X O O 4 2 6 | $$ . X O X 3 1 . | $$ . X X O O O 5 | $$ . . . X X X . | $$ . . . . . . . |[/go]

So he has to try to connect them:

Click Here To Show Diagram Code: [go]$$B $$ --------------- $$ . . . . . . . | $$ . X O O . 3 . | $$ . X O X 2 1 . | $$ . X X O O O . | $$ . . . X X X . | $$ . . . . . . . |[/go]

After the obvious :b3:

, there are two ways to go:

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

or

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

Letting black connect underneath is certain death.
So white is left to try to kill the three black stones while black tries to squeeze the eye where the captured stone was.

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

This works for white.

Thus black has to back up and try a different move 5:

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

Wife wants me to join her for breakfast, so I'll stop here.

Bill Spight · #6

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

Jujube · #7

Ha, so now I see why they didn't expand on the answer in the book, it would have taken up too much space. So looks like I was more or less right. White dies or at least it is very annoying.

EdLee · #8

Jujube, seems W dies unconditionally with :b1:

at 2-2.

djhbrown · #9

Jujube wrote:

it says: Black A is sente.

No, it's not. It's kikashi.

The Bishop speaks better Japanese than me, so you'd better check with him what sente really means, but here's my take, based on what i remember inferring from Ishi Press books, many of which he translated:

sente means: "if you don't respond, i will make an unreasonable gain"
kikashi means: "assuming the rest of the board is reasonably balanced, if you don't respond i will make a very unreasonable gain, so large that i will win the game there and then".

Since Korean commentators became popular, their common use of the Japanese word sente to loosely mean "kind of forcing" has become commonplace among Anglophones too, but the difference between sente and kikashi is fundamental.

In this position, black 7 is sente, because it threatens a follow-up move at A, which would be kikashi.

Attachment:

jujube.png [ 22.12 KiB | Viewed 11438 times ]

A is kikashi, because if white doesn't respond, black can kill the corner, as Ed showed.

When you look at the position at the top, you have to imagine the two pictures at the bottom. I'm as weak as you, and i have trouble doing that, so sometimes i ask gomap to show me what i should see; and if that doesn't help, i ask Swim.

gomap sees that white has 2 clusters, not one, so there is plenty of aji.

The shape move for black is the centre of symmetry, the red point. It's the point any kyu can straightaway see, because you don't have to be any good at Go to see symmetry.

The green point is what i reckon a Dan would immediately see first; the clamp is a standard endgame tesuji to score a few yose points, often in sente.

Here, with A in place, the green clamp does more than that; it produces a ko.

So for that reason alone, A is sente, but because there is also the red placement, A is more than just sente; it's kikashi.

A is valuable for another reason too: look at the bottom right picture to see how much it expands black's influence in the centre and even on the right as well as along the top.

PS Oh, wait.. maybe the clamp kills too... check this out:

Attachment:

jujube.sgf [256 Bytes]
Downloaded 643 times

EdLee · **#10**

Hi Jujube,

djhbrown · **#11**

EdLee wrote:

The original wording is quite clear and unambiguous, to me.

Hi, Rob!

it's all double-Dutch to me; i never was any good at seeing things in black and white.

Question about problem 7 in Making Good Shape

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