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Lee Sedol retiring

Many readers may not be familiar with the name Lee Sedol, but players of the game of Go, also known as Baduk in Korea or Wei Chi in China, know him as one of the greatest players ever. Go is a game played with black and white stones on a 19X19 grid, in which both players attempt to control a greater chunk of territory.

Lee Sedol is from South Korea, born in 1983. He was a prodigy and became a professional player at age 12 – the 5th youngest Korean player to reach professional ranks. He won 18 international titles – only one player, Lee Chang-ho, won more, with 21.

In 2016, Lee Sedol was subject of many international news articles when he took on a 5-game challenge match against an AI called AlphaGo. For many years, it was thought that it would be at least another decade before anyone could develop an AI that could defeat a top pro at Go, but AlphaGo turned this idea upside down, and has since beaten all comers. Lee Sedol managed 1 win in his games against the bot, after making what has become known as a divine move. Analysis has demonstrated there is a winning response to this move, but AlphaGo failed to find it and was forced to resign a few moves later.

Besides the AlphaGo series, Lee Sedol will also be known in the Go world for what has become known as the “Lee Sedol Broken Ladder Game”. A ladder is one of the two ways of capturing stones in Go. A broken ladder is normally a disastrous blunder. However, in this case, forcing the failed ladder led to the capture of a different group in a corner, leading to a win by resignation. What’s going on in the game may not be obvious to non-players, but here is a diagram of the game, which Lee Sedol played against Hong Chang-Sik in 2003. Those interested in some analysis of this game can find love with a simple search on YouTube.

Next week, Lee Sedol will be playing a final match, against a Korean-developed AI, known as Handol, then retiring from professional play. From the reports I’ve seen, he hasn’t announced what he will be doing after the match in lieu of playing Go.


  1. vox kadavergehorsamkeit

    i just watched Nick Sibicky’s take of the game and it would seem he agrees, not that he explicitly said so, but we would agree that move 73 was the key move that forced 74 and would, after the ladder is played through to 95, force the decision between saving the bottom right corner or the 16 stones in the ladder. Sedol’s play at 75 should not have been responded to at 76 as it was and while Nick did not say what move should have been played instead, i still like the 1-1….It is comforting to know that it was a “blitz game”. That is the players had only 20 seconds to make a move or 3 per minute. It took me a few minutes of looking at it to see where things fell apart. Given 20 seconds to figure out what was happening as white, i’m pretty sure i would have read the ladder worked for me and played precisely as Mr. Hong did.

    Watching the video led to a surprise for me. i had imagined your saying that the ladder leading to capturing a group in the corner and a resignation referred to the group in the bottom right. While that group was captured, he was referencing the shamari in the bottom left corner being killed. Wow!

    • In the heat of battle in a complex game with a severe time limit, it’s easy to see how most players would think capturing a ladder in the centre of the board is too powerful to resist. On the other hand, these are players who attack the game with considerably greater study than we do and who have been playing at a high level since they were kids. It’s reasonable to imagine either of them ought to be able to read both the immediate battles and the whole board implications more effectively than either of us.

      Also, as you and I both know, at least at our level, sometimes you see the board in a particular way, coloured by what you’re trying to achieve in an area, and become blinded to sequences that aren’t really that difficult to read. There have been many times that has happened to me, and when you merrily plop down the stone that cuts off my guys or implodes my shape, I think, oh yeah, there is that. How did I not see things that way?

      I’m pretty sure getting better at making decisions about which battle to engage in when and from where is key to improvement for me. That and getting stronger at assessing what is and is not really sente. Sometimes I’ll answer a move, thinking it’s reasonable to protect a group, then 3 or 4 moves later I’ll realize I ought to have ignored your poke, let my group perish, and instead make a bigger move, attacking a more significant group elsewhere. Sometimes it’s hard to slow down and consider these things, particularly when you get caught up in the rhythm of play as stones go walking in ways that seem normal or right.

  2. vox kadavergehorsamkeit

    It is a very interesting problem, but dare i say that white blew it? The ladder is encouraged to continue with 75, but is not really forced. If white responds by playing 76 into the 1-1 in the bottom right corner, he kills the 8 black stones and saves the 21 stones he has in 3 groups surrounding those 8 stones. His cost is minimal, the 4 stones in the ladder. Playing the 1-1 would have been worth an easy 60 points in terms of stones killed, stones saved and liberties even after accounting for the 4 stones in the ladder being captured. White should have appreciated that Sedol could read the ladder and would not have continued to pursue unless there was another reason.

    At least that is how i see it. i am fairly sure better players than myself would see things differently. But i’m a real sucker for plays that make such a huge difference.

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