Why does black defend here?

yoyoma · Post by **yoyoma** » Wed Jul 20, 2016 7:57 am

I was looking at a game On Sojin played (he is coming to the US Go Congress), and I didn't understand why black played the two moves marked below. Is there some aji around the P4 area? I don't see any way white is threatening to actually win the capturing race.

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

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

Uberdude · Post by **Uberdude** » Wed Jul 20, 2016 8:24 am

For Q1, my opponent's key point is my own? That kind of liberty making gote connection is easy to overlook. I used a similar move in the first game of the British Championship, move 59 here which garnered some laughs for being 2 empty triangles in one which actually gains liberties: http://www.lifein19x19.com/forum/viewto ... 23#p196323. (And if black plays 3 as atari at 4 white makes the false eye and squeezes/ataris from behind.)

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

For Q2 I don't understand the timing. The fact that black defended there after white's h2 connection suggests it is something to do with the fact white's L5 atari now threatens to take a stone and next capture the 3 stones (before black could play h2 atari, white connects, then tenuki to remove that threat in sente). So if that meant black had to answer L5 at L3 there would be a difference with moves like p4 threatening to save the stones (and hence win the semeai on the inside black stones) or break into the lower side and isolate the black corner. However, by my reading even with the h2 connection black doesn't need to answer L5 with L3 connection but can answer on the outside with n5 (making sure no p4 aji), allow white the l3 capture in sente and still win the semeai.

Click Here To Show Diagram Code: [go]$$Wc white can get an atari with a-c but achieves nothing $$ --------------------------------------- $$ | . . . . . X . X . . . . . . . . . . . | $$ | . . . . X . X O X . X . . . . . . 2 . | $$ | . . . O . X O O . X O . X X X O O X . | $$ | . . O , . X . . X , O . . O . O X X . | $$ | . . O X . . . . . . . . . . . O . . . | $$ | . . X O X . . . X . . . . O . . X . . | $$ | . . . O X . . . . . O . . O X X . . . | $$ | . . . O . . . . . . . . . X O . X . . | $$ | . . . . . . . . . . . . . . O . . . . | $$ | . . . O . . . . . , . . . . . O . X . | $$ | . . . . O . . . O . . . . . . . O O . | $$ | . . . O X O O X O . . . . . . . . . . | $$ | . . O X . X O X O X X . . . . . . . . | $$ | . . O . X X O O X O . X X . . . O . . | $$ | . . . . . X . X X O 3 O 4 c . . . . . | $$ | . . . O . X X X O O X O a b 7 , X . . | $$ | . . . . O X O O X X 5 X X . 8 X . . . | $$ | . . . X O O . 1 O X 6 . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

The only other possible explanation I can think of is there was the possibility of a large ko fight upcoming, and black's move eliminated many big threats, so then white didn't create the ko. But I can't see where such a ko could occur. I suppose there is also the consideration of the status of c3 (assuming white blocks at d4 as in the game later), which would live if d3 were sente, so white e4 liberty being sente has some effect there, but then the h2 connection means white can live independently if cut so I don't see that actually working.

Btw say hi to Sojin for me (Andrew from BIBA), and he likes burgers so if you want a review buy him one

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yoyoma · Post by **yoyoma** » Wed Jul 20, 2016 12:25 pm

Q1, oh yeah... It seems I still cannot count to 5 (liberties).

Q2, yeah seems P4 doesn't do anything?

Did Sojin teach at BIBA?

Uberdude · Post by **Uberdude** » Wed Jul 20, 2016 1:17 pm

yoyoma wrote:Did Sojin teach at BIBA?

Yes, he was one of the main teachers when I was there (summer 2013). I think shortly afterwards he was due to do his military service; he was studying English which I think was in part to help him get a better position there.

Kirby · Post by **Kirby** » Wed Jul 20, 2016 7:53 pm

Burgers. Maybe the source of his power.

I need to find a cow.

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Why does black defend here?

Why does black defend here?

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