Professional Kwon Gap-yong (8p), who also has been a mentor to Lee Sedol, said before the game: " Lee has already learned that AlphaGo tends to make strange moves when it faces unfavorable conditions. Lee will have more of a chance of winning the final match if he makes key moves that are difficult to read ".

I personally feel AlphaGo should be aware of the tesuji itself, but Lee Sedol's follow-up move was probably better than expected by AlphaGo ". He bites his nails and hopes that AlphaGo very soon gets a chance to make things right again ( Dia. 5 ).

The tesuji itself appears quite often in pro game records, thus it is most likely learned through the 'policy' network.

AlphaGo made a bad mistake early in the game (it didn't know a known tesuji) but now it is trying hard to claw it back... nail-biting ". He added later: "

This tesuji frequently occurs in the games AlphaGo originally has been trained on, so it is quite incredible that the program didn't learn to handle this tesuji correctly. AlphaGo looses points here (as well as ko threats), apart from the unnecessary waste of options to utilize the potential aji of it's three white stones ( Dia. 5 ).

This tesuji frequently occurs in the games AlphaGo originally has been trained on, so it is quite incredible that the program didn't learn to handle this tesuji correctly. AlphaGo looses points here (as well as ko threats), apart from the unnecessary waste of options to utilize the potential aji of it's three white stones ( Dia. 5 ).

Lee Sedol avoids that AlphaGo will foreclose the bottom right corner and extends his corner ( Dia. 5 ). AlphaGo calculates that it's three stones have enough aji to make a fight meaningful. The program apparently is unfamiliar with a common tesuji (also known as the 'tombstone squeeze': you offer two stones, subsequently throw in another one, in order to rob the opponent efficiently from the inner liberties).

Lee Sedol avoids that AlphaGo will foreclose the bottom right corner and extends his corner ( Dia. 5 ). AlphaGo calculates that it's three stones have enough aji to make a fight meaningful. The program apparently is unfamiliar with a common tesuji (also known as the 'tombstone squeeze': you offer two stones, subsequently throw in another one, in order to rob the opponent efficiently from the inner liberties).

Both Lee Sedol and AlphaGo play a very solid opening and after move 40 (circle in Dia. 4 ) the outcome of the game appears completely open from their opposing moyo and territory strategies.

At this point, it is completely unclear how many points white's move is worth (how much it could add up to) but in any case this move works well with white's other stones on the board. And pushes Lee Sedol to prevent that AlphaGo will play nobi or keima downwards to further build it's moyo.

At this point, it is completely unclear how many points white's move is worth (how much it could add up to) but in any case this move works well with white's other stones on the board. And pushes Lee Sedol to prevent that AlphaGo will play nobi or keima downwards to further build it's moyo. Both Lee Sedol and AlphaGo play a very solid opening and after move 40 (circle in Dia. 4 ) the outcome of the game appears completely open from their opposing moyo and territory strategies.

Black gets a rather large and secure corner in exchange for white's strong and balanced group at the right edge. After moves on the left, where Lee Sedol builds a solid group and white makes a well-balanced extension from the bottom left corner ( Dia. 4 ), AlphaGo plays to make influence towards the center and to build potential in the

Black gets a rather large and secure corner in exchange for white's strong and balanced group at the right edge. After moves on the left, where Lee Sedol builds a solid group and white makes a well-balanced extension from the bottom left corner ( Dia. 4 ), AlphaGo plays to make influence towards the center and to build potential in the

Black gets a rather large and secure corner in exchange for white's strong and balanced group at the right edge. After moves on the left, where Lee Sedol builds a solid group and white makes a well-balanced extension from the bottom left corner ( Dia. 4 ), AlphaGo plays to make influence towards the center and to build potential in the bottom left quarter of the board (circle in Dia. 4 ).

AlphaGo chooses to clamp and makes a base for it's three stones in the upper right (see Dia. 3 ). Then both sides cut and AlphaGo ends in sente as Lee Sedol connects his attacking stones underneath (circle in Dia. 3 ).

AlphaGo chooses to clamp and makes a base for it's three stones in the upper right (see Dia. 3 ). Then both sides cut and AlphaGo ends in sente as Lee Sedol connects his attacking stones underneath (circle in Dia. 3 ).

AlphaGo chooses to clamp and makes a base for it's three stones in the upper right (see Dia. 3 ). Then both sides cut and AlphaGo ends in sente as Lee Sedol connects his attacking stones underneath (circle in Dia. 3 ).

Black replies calmly, then plays tenuki to prevent white from making a double extension to the right (circle in Dia. 2 ). Lee Sedol presents AlphaGo with a choice: clamp and allow black to attack the three white stones in the bottom right, or

Black replies calmly, then plays tenuki to prevent white from making a double extension to the right (circle in Dia. 2 ). Lee Sedol presents AlphaGo with a choice: clamp and allow black to attack the three white stones in the bottom right, or try to fight and prevent black from connecting underneath?

AlphaGo starts off with a probing move (yosu-miru) to see how Lee Sedol will answer (circle in Dia. 1 ). On that basis white will determine if and how to complete the joseki in the bottom right.

AlphaGo starts off with a probing move (yosu-miru) to see how Lee Sedol will answer (circle in Dia. 1 ). On that basis white will determine if and how to complete the joseki in the bottom right.

in the exhilaration of victory, Lee Sedol must have concluded that AlphaGo's moyo treatment had been far from optimal and

In the fourth game, Lee Sedol exposed some of AlphaGo's weaknesses in judging the amount of aji in the program's center moyo. When analyzing the game afterwards with his team, in the exhilaration of victory, Lee Sedol must have concluded that AlphaGo's moyo treatment had been far from optimal and could be put through the mill once again this last game of the match.

a few sente moves on the outside that might come in handy later if white wants to make points there.

White especially focuses on influence and, after a few moves in the upper right corner, a battle develops for AlphaGo's meanwhile firm center moyo (Dia. 6).



Lee Sedol invades to pressurize AlphaGo further in the upper left corner and to reduce AlphaGo's potential center moyo at the same time (triangle in Dia. 6). However, AlphaGo plays a beautiful and effective response which turns around the flow of the game immediately. Now, Lee Sedol is put himself under very high pressure (circle in Dia. 6).



AlphaGo's move prevents black's invading stone to connect easily with black's group to the left, prevents an escape of the invading stone to the center to make eventually a base there, forces the invading stone towards white's strength top right, and firmly contributes to it's built up sphere of influence in the center. Moreover, the idea is that if Lee Sedol tries to live, AlphaGo can exert huge pressure on him to become strong on the outside (to reinforce it's moyo even further, see Dia. 6).







Dia. 7: Game 5, after black 81 (circle, Lee Sedol is black)

There's no other choice for Lee Sedol than to create a base. But in exchange AlphaGo gradually continues the work on it's moyo (Dia. 7). AlphaGo keeps pushing Lee Sedol's group and ends in sente, then builds further on it's moyo at the bottom side (triangle in Dia. 8).







Dia. 8: Game 5, after black 91 (circle, Lee Sedol is black)

In a complex middle game Lee Sedol is forced to find efficient ways to prevent AlphaGo from cashing in it's entire moyo. The question is whether AlphaGo can make enough points in the center to outweigh Lee Sedol's already secured territory in the corners (Dia. 8).



Black has about 70 points secured territory, white has about 30 points together in the upper left corner and it's center moyo. Taking 7.5 komi into account this means that white can only win this game if the program gets at least 35 points in the bottom left corner and edge (without giving black any extra compensation for this). Alternatively, white has to find ways to collect additional points in the center. This crude estimate suggests that the game in this position is still open and undecided.







Dia. 9: Game 5, after white 122 (circle, Lee Sedol is black)

The game is developing slowly as Lee Sedol first somewhat contains AlphaGo's center moyo, and then creates a group in the bottom left (Dia. 9). With white's calm responses initially some strength is built though it is unclear what white does want with this. After AlphaGo's extension (circle in Dia. 9) it becomes clear, however, that Lee Sedol has to make a base with his group at the bottom side (or must connect). And that white is trying to lock up black.







Dia. 10: Game 5, after white 136 (circle, Lee Sedol is black)

Black connects his group underneath with the right corner and gains some extra points while white builds some force and meanwhile significantly reduces black's influence at the lower right. Then, AlphaGo plays a magnificent split move and nice counter attack (circle in Dia. 10) that adds burden on black and let's white stones working together optimally.





It is difficult for black to decide what is the best strategy in this position. Lee Sedol can't afford to give up his center stones and at the same time has to minimize white's center moyo as much as possible. AlphaGo's strength at the lower side is being used primarily to keep pressure on Lee Sedol with a range of possible cut actions.







Dia. 11: Game 5, after black 183 (circle, Lee Sedol is black)