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Comment by awwducks | Hacker News Reader

Perhaps the last big question was whether AlphaGo could play ko positions. AlphaGo played quite well in that ko fight and furthermore, even played away from the ko fight allowing Lee Sedol to play twice in the area.

I definitely did not expect that.

Major credit to Lee Sedol for toughing that out and playing as long as he did. It was dramatic to watch as he played a bunch of his moves with only 1 or 2 seconds left on the clock.

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Well, we don't actually know AlphaGo's true strength in Ko matches because the Ko setup wasn't that complex. There wasn't a lot of trade points available.

A possible explanation is:

During self reinforcement learning, AlphaGo learned to minimize Ko potential by maximizing its probability of winning through diminished available Ko moves.

It would be interesting to see how AlphaGo would be able to capitalize on a game that emphasized Ko play, but that would take more time with AlphaGo to emphasize that kind of play.

edit: I'm not sure why, but I think Lee Sedol is partly holding back, or not playing at his maximum ability. It feels like these games are more along the lines of query games.

I look forward to the next two games because I'm 100% certain Lee Sedol is going to query the AI with some new queries.

When you have a minute, even if you already know your move, you take the rest of the time to read the plays. You don't play your stone until there's only 1 or 2 seconds left, unless the play is so trivial that you need to see your opponent's play in order to continue reading. Every time Sedol played with 1 or 2 seconds left, his rush was only to get the stone on the board, not because he suddenly knew what to play.

> as he played a bunch of his moves with only 1 or 2 seconds left on the clock.

That's on purpose to make full use of time and think about the next move

As a spectator, I was on the edge of my seat :)

As a 3d amateur, I'm really curious about when he resigned. It really seemed like he was playing the position out to go for the win (or perhaps to see how AlphaGo would fare in ko). It didn't look like he was searching for a place to resign.

The AGA commentator (Cho Hyeyeon 9p, at https://www.youtube.com/c/usgoweb/) had already been calling the game completely hopeless for Lee Sedol for nearly 2 hours at that point, estimating Lee down by at least 20–30 points before komi, unless by some miracle he could win the ko fight.

Right, all about one or two wrong moves by AlphaGo. He still had a chance around the time Lee started to play the bottom of the board. But AlphaGo did not fall for the trick. I believed the English commentator said Lee could build a ladder but wasn't sure if he meant to say whether that technique would defeat AlphaGo or not.

I did not watch that stream, but IIRC the first move Sedol played in the bottom was a ladder breaker, specifically because white had a difficult-to-see ladder that worked a move earlier than black's ladder on the right side. At that point, there was no way Sedol could win, so the commentator you referenced probably did not mean any such ladder would defeat AlphaGo.

Edit: M5 was definitely played as a ladder breaker, so the above is correct.

Ah, neat, thanks for the link. I didn't look to the AGA channel because I figured there wouldn't be a stream since Myungwan was doing live commentary.

I think from a technological perspective there's very little question that AlphaGo could play ko. I would have imagined that AlphaGo would be better at ko than most human players since it's a question of balancing risk across the entire board. Human players might be more likely to be exhausted and choose suboptimally by the calculation deciding between different stakes on the board, but MCTS will correctly optimize for the long term potential of each major branch in the game tree.

So I'd be very surprised if that turns out to be the trick. Things that are hard for human players are not at all necessarily AlphaGo's weaknesses.

Don't have the link offhand, but I read on Reddit that Lee Seedol and a few other Go professionals pulled an all-nighter coming up with ways to beat AlphaGo, and one of their guesses was that AlphaGo would be bad at Ko's. I think the reasoning was because that hadn't happened in the games, so they assumed it was avoiding them.

>so they assumed it was avoiding them.

I think us humans made a critical error in that line of thinking.

It didn't avoid ko because of the risk of loss.

It avoided ko because of the lack of strategic win.

He was just making effective use of his byo-yomi. Pro players are used to that.

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