Yoonyoung Kim 4p made a video review of this game, linked below. Also, the broad strategic thing which struck me the most (apart from all the ko trades) was how Ke Jie managed to make himself a nice chunky centre territory with a smattering of weak stones. Yes, he spent a few gotes to do so which enabled black to win the lower left ko, but I wonder if black missed a chance to harass white a bit an stop him from so efficiently turning a liability into an asset. A few ideas for investigation with LZ later:
- move 65 or 71 cap at m11,
- instead of e13 can black get d13 c13 d12 c12 e11 in sente with w answer d10 and then k11 or would white tenuki not d10
- 107 necessary? Can black do something in the centre first like m12? m12 n10 k11 looks pretty nice to make a black instead of white centre, how does it compare to sacrificing m7?
- 143 conceded ko, could black do some middle things first, maybe there's a way to probe on n13 stone: later during ko it's light, but now when white is still dreaming of attacking black q14 he might want to save it.
- white j15 and k17 very cool and flexible
- once the lower left ko became direct centre threats wouldn't be big enough
- painful that black had to live with r15 and couldn't o16, that looks like a long life and death problem so did Kim reckon he would die, or thought he could win this way?
- q1 too late to do middle things I suppose, but still seemed odd place to spend a gote, was it to avoid white's 1st line sente endgame?

https://www.youtube.com/watch?v=4XvnRDvyKZo

Can someone help me out? I have a hard time understanding white 156.
G1 kills the black group in double Ko as far as I can tell, which seems to be a natural choice.
I can see that white might have some trouble with a black stone at B11 and a dobule Ko is not as clean as a normal kill, but I am still suprised by the decision of
Ke Jie. Does anyone have some insight or even just engine analysis?

Good question Leon, and nice spot of g1 (which I didn't see during the game). Here's my idea:
- the ko is not just about life/death of black/white in the corner, but also about the eyes of the outside black group. Working backwards:
- white could have simply answered black 145 at c8 and black's corner would be dead rather than the approach ko it became in the game (for which white got a few moves to build his centre), but then black would get d6 in sente which builds some handy eyes in e6 area, and then presumably play something in the centre.
- Given that white didn't answer, and if we make the assumption this was a reasonable decision of Ke Jie and not just misguided human fighting spirit (which is not as simple as does bot agree: a bot may be confident it can play out the half point win with c8 answer whereas Ke might see that as too uncertain and actually prefer a more complicated game where he can demonstrate his superior skill), then that explains Kim's earlier decision to give up on the ko (for now) and take the q12 profit and attempt to force from the outside with d7.
- so if white plays g1 then he loses 1 point as eventually he'll capture the stones anyway when black fills dame, black still gets the d6 forcing move for eyes, and because of the double ko infinite threats black can win any other ko such as answering e9 at e8 which means that group is practically alive in sente and he can then turn to the centre. So white played the atari because he wanted to make black's outside group weaker and then if he wins the ko it's in big trouble without d6 sente (even more so after white f8)
- so Ke makes the ko bigger, thus Kim feels he can't answer the q10 threat (which makes Ke's previous centre moves during ko better as now black's group is weak so he can't be aggressive in the centre), and also creates weakness in g8 connection which makes the cut for desserts we saw later in game.

Semi-Final;


Park Junghwan defeated Ke Jie by 1.5.
Park Younghoon defeated Dang Yifei by 1.5.

I am confused by the result of the Ke Jie/Park Junghwan game. Isn't the tournament using Chinese rules with 7.5 komi?

Edit: Park younghoon won the other semi final by 1.5 points.

go4go says white won by 0.5. Yet another win for white between Park and Ke, that's 15 wins for white, 2 for black (both Ke) between these top 2 players for whom nigiri essentially decides who wins (Park 9, Ke 8 wins).

I predict that Park will win the Chunlan cup !

Very happy to see Park Younghoon's renaissance. I will be pulling for him.

The ending of the game must have been very disappointing for Ke Jie. According to the commentators, Ke was winning after living in the center and taking the ko—until he made a single mistake in the endgame, where 229 should have been at B11. This apparently flipped the result to W+0.5.

Hi, thanks for the answer, I think I can understand this a bit better now. Ko fights are quite difficult, aren't they?

Final;
Park Junghwan vs Park Younghoon
1st game - 6/25 11:30 am
2nd game - 6/27 11:30 am
3rd game - 6/28 11:30 am

1st game;

Park Junghwan defeated Park Younghoon by resign.

The game, Park Junghwan was black. One interesting thing from a quick LZ review was how often it thought black should defend at g16 throught the middlegame. White g17 wouldn't cut with black g18 g16 combo but makes an option to scoop out the territory and eyes, and LZ sees g17 g18 and tenuki as a beneficial exchange.

Upset in game 2 Park Junghwan (white) made a massive overplay/blunder at 96 and Park Younghoon is now at 99% or ~28 points lead (says Yike bot)! At least white profit from the trade at top right is more certain (assuming L9 outside cutting stones don't die, how much of the AI judgement is based on black using that aji to stop white making much on lower side?) whilst the left side white can still try to make a mess and hope for black mistake.
Update: after a long think Park Y played g10 extension instead of saving the top left stones, claiming it is sente for L8 and resurrecting the dead group. If that's true it captures the 5 cetnre stones in sente for good aji, but Park J resisted and Younghoon played the wrong net, looks like he's trying his best to lose! What a reversal this will be if Junghwan pulls it off.

2nd game;
Park Junghwan defeated Park Younghoon by resign.

Park Junghwan is new Chunlan cup Champion!!!!!!

Here's LZ 229 at 3k playouts view of this rollercoaster of a game:



And some commentary on the crucial moments with variations.