How to Beat KataGo at 4 stones


 


This is the beginning of a 4 stone game with KataGo. This version is what you get when you download it and accept the initial settings (5 seconds a move) playing on a DeskTop, meaning it's much weaker than versions playing on network computers, but it's still super strong.  However, it does handle some corner situations in a way that can be taken advantage of, which is the key to the strategy to beat it at 4 stones.

In particular, if you make an extension of 4 spaces from the handicap stone, it sets up a situation which can be taken advantage of later. This explains the odd looking moves of 2 and 10. The opening strategy is to have KataGo invade in two corners, the Upper Left (UL) and Lower Right (LR), and kill these groups later.


Here we are a couple of moves later. Note how KataGo left the LR corner. It typically does this when invading a corner with a 4 space extension.




Here we see KataGo has invaded the Upper Left in the same way. Black in the UR and LL tenukied when W entered the corner, in order to set up the corner situations in the UL and LR. One of the challenges is to make the groups strong where KataGo has the advange because of having tenukied. The UR and LL show a couple of approaches that work well.



Key moves in the process of killing the corners are 26 and 44. 26 it almost always answers with 27, while 44 it typically ignores, even though 44 threatens to kill it. Here I waited until a good opportunity where I though my group was strong enough that I could ignore a move to play it.  The move was 45, an excellent point, but I saw that 45 and 46 were miai, and the group would be strong by getting one of these.


Here 52 sets up some aji which 58 threatens to take advantage of. In addition to being a fairly big threat, capturing the 3 stones (19,21,23) secures the group. Although this particular group was not in danger, it's a handy technique. I still haven't gotten around to killing the UL group. If you wait too long, it will wake up and defend it, so killing it, and the one in UL is a high priority, before the opportunity goes away.


The same technique was used in the LL as UR, and here the group is not nearly as strong, so having the option to capture the 3 stones (1,3,5) really helps the Black Group.

The White corner group in the LR is dead. The one in the UL is threatened. In order to accomplish this, moves 65 and 69 were ignored. Because of the aji left by 62, the LL group was able to fend for itself.


White made forcing moves in the LR until move 85, putting some pressure on the LL group, which was secured by 86 and 88. When W played 89, B had time to play 90, killing the UL group.

At this point, the game is essentially over, as all Black groups are safe, and the loss of the two corners is too much to overcome. Following is 16 moves later:



Black was able to capture all 4 corners, all groups are secure, and there is enough thickness to prevent White from making a large territory in the center. KataGo estimates Black to be ahead by about 50 points, which is roughly the advantage of the 4 stones. Thus this strategy was sufficient to keep the opening advantage for over a hundred moves.


This is the final screen shot, where KataGo resigned. It typically resigns at move 153 if its percentage is low enough. The final margin was estimated to be about 47 points.

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