Interesting go problem from a real game

gamesorry · Post by **gamesorry** » Thu Sep 01, 2016 10:19 pm

I recently came across an interesting game in one of the online tournaments:

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

The question is, after white's move, can black defend the corner without a ko?

dhu163 · Post by **dhu163** » Fri Sep 02, 2016 3:10 am

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

I think so

Shaddy · Post by **Shaddy** » Fri Sep 02, 2016 3:16 am

dhu163 wrote:
$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X X X 3 |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X O 1 |
$$ X X . O X X . O X O 4 |
$$ . X O . . . O O O X 2 |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O . O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$

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

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

Ko. I don't see any way for Black to keep the whole corner, at least the 2 stones on top are going to get ko'd.

Tryss · Post by **Tryss** » Fri Sep 02, 2016 3:19 am

Edit : same idea as Shaddy

White won't play like that in this line :

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

skydyr · Post by **skydyr** » Fri Sep 02, 2016 10:57 am

The empty triangle looks good to me at first, but...

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

However, does black need to play :b3?

Click Here To Show Diagram Code: [go]$$B $$ ---------------------- $$ X . X X O . 8 6 9 7 0 | $$ . X . X O . X X W 2 4 | $$ X X X O O . . O X 1 . | $$ . . . . O . . O X . 3 | $$ X X . O X X . O X O 5 | $$ . X O . . . O O O X . | $$ O O O X X X O X X . X | $$ . O X X . O . O X X X | $$ . . . . X O . O . O X | $$ . . . . X O O . O . O | $$ . . . . X X X O . O . | $$[/go]

This seems to work:

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

However:

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

So perhaps:

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

And now black has enough liberties for the fight.

Shaddy · Post by **Shaddy** » Fri Sep 02, 2016 11:34 am

skydyr - still not enough liberties.

skydyr · Post by **skydyr** » Fri Sep 02, 2016 12:18 pm

Shaddy wrote:skydyr - still not enough liberties.

In the last diagram? I don't see it, so could you explain?

That said, I think on re-examination, white can play at :b9:

instead and black can either play an unfavourable ko or connect and let white connect under.

Edit: Nevermind, I'm still counting four for some reason.

phillip1882 · Post by **phillip1882** » Sun Sep 11, 2016 3:51 pm

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

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

now what for white?

Schachus · Post by **Schachus** » Sun Sep 11, 2016 4:44 pm

Phillip:

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

Black is captured, because he cant approach a, so white b next captures.

gamesorry · Post by **gamesorry** » Mon Sep 12, 2016 12:46 am

Thanks, so it does seem that a ko is unavoidable.

FYI, the original game is here. I missed white's refusal at (4,1) at first glance.

rafaelclp · Post by **rafaelclp** » Mon Sep 12, 2016 10:18 pm

Schachus wrote:Phillip:

$$W
$$ ----------------------
$$ X . X X O . . . X . . |
$$ . X . X O . X X . X . |
$$ X X X O O . . O X O . |
$$ . . . . O . . O X a O |
$$ X X . O X X . O X O b |
$$ . X O . . . O O O X X |
$$ O O O X X X O X X . X |
$$ . O X X . O . O X X X |
$$ . . . . X O . O 1 O X |
$$ . . . . X O O . O . O |
$$ . . . . X X X O . O . |
$$

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

Black is captured, because he cant approach a, so white b next captures.

I still don't get why black dies. Wouldn't 5 below save black if white played as expected above?

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

Edit: oh, right, it still ends in ko

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Interesting go problem from a real game

Interesting go problem from a real game

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