Lose a ko to win the game

    Keywords: Strategy

One technique to seal a game when you are in a winning position, is to create a ko in the opponent's large prospective territory, preparing to lose it and play elsewhere twice. The prospective territory becomes effective territory, while you choose an area to play twice. This simplifies the game. Given your being ahead before the exchange, the simplification is very likely to result in a clear advantage. The idea of making a ko when ahead, for simplification, is perhaps not intuitive, since a ko feels inherently complex to the amateur, but we can see it a lot in professional play, in particular in the games of Go Seigen and Gu Li.

(examples to be added)


See also:

hhw: Would it be better to call this page "Force your opponent to start a ko that you can lose"? Since the idea is to start a ko when you're ahead. Then, as normal, you would win the ko if you gained more than your opponent's threat. But in this situation you would also be happy to make a threat smaller than the ko (or just play a big endgame move) if your lead is kept after the territory solidification that results from your opponent winning the ko and you playing twice.


unkx80: The following game between Takagi Shoichi (Black) and Lin Haifeng (White) may be an example. There is no commentary regarding the ko.

[Diagram]

Moves 131 to 140

unkx80: B9 cannot play at W10, or it will result in White a, Black b, White B9, resulting in a capturing race that Black cannot win.

[Diagram]

Moves 141 to 150 (B7 at black+circle)

unkx80: I guess that the aim of starting this ko is to get both W8 and W10 for compensation.

[Diagram]

Moves 151 to 160

unkx80: After the White cut, Black's framework at the bottom vanished in no time. B9 is needed to settle the large dragon.

Dieter: As a minor remark, I believe responding to B9 is much better than W10.

[Diagram]

No ko

Dieter: In order to understand the strategic concept, we must evaluate what happens if White does not use the ko. Suppose White kills locally, then B3 leaves bad aji, because a now is sente (small reading exercise). Or will B3 be played at b?

So I think part of the purpose of the ko was to eliminate the bad aji at the top, by forcing Black to play the threat at B5 (two diagrams ago).

unkx80: I don't claim to fully understand this game, but I suspect B3 will be played at b. Then when White cuts at B3, Black may give up the two stones.

Dieter: I understand the reasoning, but doesn't a clean capture of the upper left, as would happen if Black gives up the 2 stones, simplify the game even more?


Dieter: Here is a game I recently played, in which I was reminded of this strategem. It is probably not a good example, because I was already largely ahead, but on the other hand it achieves the goal of removing aji and pushing the game towards a more clearly defined win. Moreover, I consciously applied the idea, being one of my favourties:

[Diagram]

Starting position

I could play the monkey jump with a but I saw the opportunity to start a ko I could afford to lose.

[Diagram]

Moves 172 to 181

W5 threatens to make two eyes inside Black's corner. At W10 the ko starts.

[Diagram]

Moves 182 to 191 (8 at 3)

My first threat W1 is an obvious one, likewise Black threatens to revive his group with B4. With W7 I play a minor threat, which however is worth about 10 points and gives two eyes to my group, so that I don't have to worry anymore about the aji around a. I suspect Black did not expect the snap-back at W9, which makes the move 2 points bigger and sente.

(Incidentally, this is part of ko psychology. Play a gigantic threat first. Then play a threat which is much less severe, but probably just enough for you. The opponent may be lured in to relief that it's only going to be as bad as this. Then you get what you want. It is similar to negotiation tactics, where you irst make an outrageous demand, to then settle for what you really want. Especially when you are not ko master such devious tactics may be helpful.)

[Diagram]

Final position

Black has made a few points in the corner, but White took a chunk out of the big territory, making his group 100% alive in the process. At the low dan level, this completely settles the game.


This is a copy of the living page "Lose a ko to win the game" at Sensei's Library.
(OC) 2011 the Authors, published under the OpenContent License V1.0.
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