In another thread the issue of time limits of professional games, and the effect on the quality of play and amount of mistakes came up. JF lamented the shorter time limits of modern Go (particularly outside Japan) and suggested they led to a more risky, probabilistic style of Go than "soba" Go (more compromises and trades for 'market price'), and that a soba-style player (I don't know what modern top pros are such, a Japanese player like Takao perhaps?) with 6 hours might have done better against AlphaGo than Lee Sedol did (with 2 hours). (Whilst I agree Lee Changho in his prime, or Go Seigen could well have done better against AlphaGo, I doubt any of the current top Japanese players would even though they still play 8 hour games). Anyway, I thought I would actually look at some pro games with in-depth commentaries and see how many mistakes they make to get some real evidence to inform the discussion.
For starters I am currently reading GoGameGuru's book Relentless on the Lee Sedol vs Gu Li Jubango in 2014. Those games had 4 hours each. Next up I will look at a Go Seigen game from one of JF's books (I have Kamakura (vs Kitani) and 9-dan Showdown (vs Fujisawa)). Then I will try to find some modern fast game with an in-depth commentary (maybe from gogameguru, could be hard to find), and perhaps a recent 8 hour Japanese title match. Of course some commentaries will be more critical than others, mistakes have different degrees so you can't just count them, but I think this will be an interesting exercise.
So let's start with game 3 of the Lee Sedol vs Gu Li Jubango, which was played with 4 hours each (pretty long for non-Japanese tournaments, most are 2-3 hours these days). Thanks for the analysis of course go to authors An Younggil and David Ormerod, which I am summarising.
Mistakes:
1)
: Driving tesuji usually good but here directly 25 better. Then white extends at black 23 and black hanes underneath at o18. White is then not as thick as in the game. That thickness made the left side black thin.2)
: Lee probably wants to exchange this for o3 before playing r5, but white's resistance was powerful and he should have just played r5 directly.3)
iron pillar at c10 better.4) b101: should push at 102 first (Note Gu's perfect opening play to here!)
5) w112: slightly passive, just connect is better but white is ahead so he fell back.
6) w116: should atari d7 then g8 then d12.
7) w124: should be e6, Gu was playing too slackly in the fighting due to his lead, Lee is in his element in this fighting in disadvantageous areas. The game was even by b131.
8) b135: big mistake, should b11 first, if white snips off the tail with e5 like in the game then black can get g9 in sente to seal the centre and then tenuki to play o12 (that's if white answers g9 at j7, if j8 then no seal and tenuki is to e14). Gu regained the lead to 146.
9) b147: losing move, should h9 cut. Lee's self-indulgent plan was that white would fall back to h3 and then he can cut and has gained 2 points.
10) w178: f13 would kill to end the game quickly and white can cope with h9 cut. This cut is bad because k12 in sente allows black k10 after h9 cut to make a ko shape to capture the right side in sente.
11) b185: d11 is a better way to live as black then has ko aji with the dead stones in the bottom left.
White won by Resign, 222 moves.
"We saw some careless moves in this game, which is unusual for Lee and Gu". Also Relentless mentions Lee said the tournament schedule was very too tight (this was the 3rd game between these 2 players in a week! so Gu had the psychological advantage).
Brilliances (according to an ill-defined threshold!):
-
- 
: white flexibly compromises as black has bad aji with a ko in the corner, and another ko shape outside that's hard to fully digest.-
delicately reaching out to the right side stones (even without this the 6 white stones at s4 aren't totally dead despite black's s1 defence: with s6 white can either create a ko or seki in the corner, or if black allows t8 connection and tries to kill all white can live with a 30+ move long sequence using the n14/o13 stones!).- b123: clever multi-purpose move to manage the left
So we have 11 mistakes in this 4 hour game, next up a Go Seigen game...
: Kitani was afraid of the avalanche if he attached (it wasn't as well explored back then, Go's innovative inwards turn hadn't appeared yet) so played this full-wll knowing it was unusual, but if I would call it a mistake in a 10 kyu game review I have to call it a mistake even when played by Kitani.
Go said it should be kosumi to j4 to avoid giving white momentum to settle, as 
wedge and then 
hane were sharp, and this was the cause of black being outplayed in the opening.
minor, and others might disagree, but Kitani says this should be capture to avoid the peep at L7. Also 
is not so great as overconcentrated pushing from behind, but not much choice given earlier mistake. Cancel out?
Go says "questionable but perhaps inevitable" as induces white to fix thinness with 48. Fujisawa Hosai preferred c13. Go later said d13 better, but rejected that for weakening top. Kitani thought 47 as played was good.
. But I am sticking to my guns in being undeferential and calling it a mistake. Searching my database (mostly GoGoD) for the below pattern (with a black 4-4 behind so that black's extension from the wall of 2 is a double purpose extension from the 4-4 as in Go's game) I find only 2 hits: one is Kitani in that game and the other is a KGS 17k against an 8 kyu me which is hardly illustrious company. (Of course there could be games with it not in my database but it's clearly off-piste).
