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By Lee Han-soo, Park Si-soo
Lee Se-dol stepped into the venue for the after-match press briefing with a beaming smile on his face. His trembling high-tone voice laid bare the excitement he had after three consecutive losses to AlphaGo, which dealt a severe blow to his hard-won reputation. At the same time, he did his best to look calm and maintain his composure.
The following are comments from Lee, AlphaGo developer Demis Hassabi and other people involved in the game.
Lee Se-dol: I don't think I've ever felt so good after winning just one match. I remember when I said I will win all or lose just one game in the beginning. If this had really happened ― I won 3 rounds and lost this round ― it would have had a great bearing on my reputation. However, since I won after losing 3 games in a row, I am so happy. I will never exchange this win for anything in the world.
Demis Hassabi (AlphaGo developer): Congratulations to Lee Se-dol for this brilliant victory. I think he has again shown why he is a legendary go player. Lee Se-dol was an incredible player and he was too strong for AlphaGo today. AlphaGo started off well it estimated that it was doing very well in the middle position. But then because of Lee Se-dol's fantastic play, it was pressurized into some mistakes.
We are also very happy because this is why we came here to test AlphaGo to its limits and find out what its weaknesses were so we can try and improve the program. We need a creative genius like Lee Se-dol to find out these issues and actually expose them. I also like to congratulate Lee Se-dol's fighting spirit that he was able to play so brilliantly today after three defeats I think it shows incredible fighting spirit.
For us this is very valuable we are not sure what happened yet and when we go back to the U.K and analyze the game carefully and look at all of the statistics and figure out what happened we will improve and fix it.
David Silver (AlphaGo's main programmer): I would also like to begin by congratulating Lee Se-dol for his brilliant win. Well deserved. One of the interesting things about AlphaGo is that we developed it to learn for itself. And this means that it may have holes in its knowledge and we needed strong enough players to find these holes.
So one of the main reasons we came here was to have a really strong player, an amazing player, to push AlphaGo into discovering where these holes are. And today in this game we saw an amazing sequence in the center where Mr. Lee was able to really push AlphaGo to expose its weaknesses and for us this is really valuable knowledge and we are looking forward to taking this knowledge and using it to learn more about our systems and improving them; and how we can learn more and hopefully make greater progress in the future.
Michal Redmond (English commentator): Congratulate Lee Se-dol on his win. I think AlphaGo again played an interesting game. In the middle of the game Lee's move 78 was a brilliant move and took me by surprise it will take most players by surprise and I believe AlphaGo was taken by surprise as well. This move was part of an entire sequence of moves and it showed Lee Se-dol's strength.