This is an impressive achievement. However there are many subtleties involved when humans play against computers. I think only time can tell how big a breakthrough this really is.<p>It is telling that AlphaGo only won 3:2 for the informal games. As a computer doesn&#x27;t know the difference between formal and informal this seems to indicate that Alpha isn&#x27;t truly above Fan Hui in strength. Also the formal games were played with fast game rules, which may be particularly advantageous to computers. Unlike chess go accumulates pieces on board throughout the game. Towards the end there are many stones on board and it is easy for human to err while the search space (possible moves) actually gets smaller for the computer and there is no doubt that computer has stronger book keeping capabilities. So to fairly evaluate human vs computer we may need new time rules different from human vs human games.<p>The paper does not disclose whether the trained program displays true understanding of game rules. Humans don&#x27;t just use pattern recognition, they also use logic to evaluate game state. While this could be addressed by the search part of the algorithm the paper doesn&#x27;t appear to give any indication on whether this was studied. For example, the board position strictly speaking does not determine the game state due to ko rules (so the premise of the paper that there is a valuation function v(s), where s is the board position, that determines game outcome is incorrect). It would be particularly interesting to see how the algorithm fares when there are multiple kos going on at the same time. Also it would be interesting to see how well the algorithm understands long range phenomenons such as ladder and liveness. With a million dollar challenge in the plan it is understandable the Google team may not want to disclose weaknesses of the algorithm but in the long run we will get to know how robust it really is.<p>From my experience playing against conv nets I would say if you treat your computer opponent as a human it would be like playing against the hive mind of a group of experts with infallible memory and it is not to your advantage. So one would be better off trying &quot;cheat&quot; moves that human experts do not use on each other and see how well the computer generalizes. Without search and with neural nets alone it is clear that computers do not generalize that well. So it would be interesting to see how well search and neural nets work together and if someone could find the algorithm&#x27;s weak spots.