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February 2001's Go Answer of the Month

Dia 1 - 218 & triangle fight a ko.

Dia 1

This is from a game I played over the Christmas break.

At the point of the snapshot shown in Dia 1, we were fighting the ko shown. I'm not sure if we should have been doing this, but anyway ...

This month's problem is to look round the board and identify ko threats. Preferably working out roughly how big they are and how to play to maximise the number of threats.

The results will be derived from the game and my own analysis. However if any (and all) of you doing this could email me your thoughts, it would help with the answer next month.

I had a few emails about this, and they were basically answering the question of how to play this game and how to play this particular ko. I wanted to avoid that and just talk about ko threats,

Because of this, I'll add a small discussion of this ko as well as discussing the threats.

A ko threat tries hard to be sente. A move that doesn't need to get answered is a non-threat. Also a threat that requires a reply tothe "ko answer" is a gote sequence and that is also bad. What you want from a ko threat is a move that is worth sufficient that if your opponent decides to end the ko, you get equal or greater compensation with the followup to the threat.

Dia 2 - Black ko threats.

Dia 2
18 at triangle

The Black threats are the odd numbered moves here, White's "ko answers" are the even numbered moves. Obviously in a real game the ko itself and white threats would be intermingled with these.

1, 3 & 5 threaten to kill White's top right corner and is thus huge. 7 threatens to rescue black prisoner's inside white territory and is worth more than it looks (~15 points?). 9 is not a big threat, only about 8 points, but 11 thretens black 12 which would make a mess of white's top group, maybe even killing it. 13 and 15 try to nick a few points from the corner group, but won't kill it. 17 atari's thre stones.

Black has enough threats here to handle a fight and there are a few more endgame sente pushes he can try.

Dia 3 - White ko threats.

Dia 3

White is much worse off for threats. 1 is huge, potentially killing the group. 3, 5 & 7 are fairly small - on a par with the few stones being fought over in this ko fight.

Dia 4 - Why isn't white 1 a ko threat?

Dia 4

Initially I expected white 1 to be a valid threat to cut off half a dozen black stones on the left. However as this sequence shows, If white takes the profit from the threat, he loses the ko and loses his stones at the bottom. A bad exchange.

Now to review the game itself and this particular ko.

Dia 5 - End the ko quickly.

Dia 5

In the light of the above, White can't really fight the ko and needs to end it quickly. Assume Black makes move 1 from Dia 2, answered by 2 from Dia 2. Black 3 takes the ko, white 4 abandons the ko and makes an eye below. Then black 5 at triangle connects the ko.

If the game is counted in this situation, white is ahead by around 15 points, more than the komi of an even game.

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