Book Club. Tesuji by James Davies, Chapter 4. Ko

Book Club. Tesuji by James Davies, Chapter 4. Ko

I’m just starting this chapter, so these are initial thoughts. Will post more later. Meanwhile, join me in reading this chapter!

I have so many questions about ko. And I think ko fights can be really fun. When does it make sense to start a ko fight? When to ignore them? When to start fighting the very small ones? Looking forward to this chapter.

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Basically ko is half value because it will take 2 moves to solve it. Ko is handy when there is no other way to escape (like when reducing a moyo) or to live. Ko teach you to not waste ko threats during the game and to not offer too many (solid play).

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Evaluating kos is hard… At least try to determine if, in case you lose the ko, the damage won’t be too big, and in that case, go for it.

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Some example situations of when to make a ko might be when it doesn’t cost you much, in the sense that if you win you kill an opponents group, or maybe cut off part of a group and the alternative is they just get to stay connected.

Those in some sense might be called “flower kos” or picnic kos, where the opponent has much more to lose than you.

It’s tricky to evaluate the size of kos precisely and it could probably be left to near dan level without affecting most of your games I imagine, while knowing a few heuristics like “there’s no ko in the opening” or that Half-point ko at Sensei's Library. (In the sense that ko counting was a Dan level lecture at the European go Congress :slight_smile: )

Another kind of situation is where you can’t live cleanly in an opponents area, but if you can make a ko, where the alternative is to just let them have the points it’s possibly better to try the ko - in the sense that when they win they just keep the points they have but you get two moves in a row elsewhere.

That’s at least one takeaway from ko - is that when you lose you often get two moves in a row somewhere else and so that in itself is valuable.

Antti Törmänen had a lecture on Cockroach style in which ko tends to feature because it’s kind of being resilient and not dieing with groups

It might be a bit much but it’s fun :slight_smile:


Cockroach style: I love that denomination!


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I’ve read this chapter with a great sense of inadequacy. It’s going to have to be good enough for now. After the new year I will pick up with chapter 5.

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Did you have anything in particular that you found interesting, difficult, confusing etc?

I feel like it’s good anyway to have just read it and be aware of kos, to have them subconsciously there and when they come up they might trigger some memory of this chapter.

On the other hand, you could read an entire book about kos if you wanted to :slight_smile: So there’s always lots to learn :slight_smile:

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Which book are you referring to?

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The one above is All about Ko by Rob van Zeijst & Richard Bozulich.


I’ve actually had a great time with some ko fights. Maybe I’ve just fallen into them more than I’ve understood the decision making around them. but you’re right, I won’t be any poorer for having grappled with this chapter a bit.

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Pre-ko evaluation, recognition of the opportunity to form a ko sometimes, knowing if a ko is a good or bad idea in a given situation.

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Jin Jiang divides ko in 6 types:

  • Direct Ko: Life and death of both sides depends on one move. The problem can be resolved on the next move after capturing the ko stone.

  • Approach Move Ko: In this type of ko at least one of the players has one or more external liberties. If there are more than two external liberties, this ko should not be fought, because if the situation is not handled correctly one can lose more than one can gain.

  • Double Ko: This type of ko results in the never ending back and forth capturing of ko stones. Three possible results: one side is killed, a seemingly dead group is revived and seki.
    Double ko’s can be used as an unending source of ko threats for another ko.

  • Two Step Ko: To finish a situation like this one has to win two consecutive ko’s. Often this is not worth to do so.

  • Ten Thousand Year Ko: the author does not describes this type of ko. Sensei’s Library does so however: A ten thousand year ko is a kind of ko position where either player can initiate the fight but the player who does is at a disadvantage, since the other player will then be the one to take the ko first. One player (or sometimes both) also has the option to make the position into sekiinstead, the likely outcome if neither side has the stomach for the ko.
    Since neither player may be eager to fight the ko, it can remain on the board for a very long time (ten thousand years). In fact, the game can end with the position remaining unplayed, in which case it is considered a seki.

  • Miscellaneous: Repeating Ko Threats, Triple Ko and Unresolvable Ko Threats: Doesn’t happen often, better say: hardly ever. Both sides are unwilling to give an inch, so this can go on and on. Japanese rules often decide this as having no competitive rsult: jigo.

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No but i am not sure it’s still the rule:

a loss for both players, not a jigo.

is something else as no competitive result.

But I am certainly no rules expert, maybe @yebellz can shed some light on this.

Jigo, no result, and both players lose are three distinct outcomes that can only occur in different situations.

  • Jigo means that a game has ended with scoring and the outcome is that the players are tied in points, which can only happen with integer komi.
  • No result occurs if the game winds up stuck in a loop (and the players agree to end the game as no result, rather than one of them breaking the loop). See Odd Cases 🤔 in the Japanese Rules - #14 by yebellz (and subsequent posts) for further discussion.
  • Both players lose occurs if both players have passed and then they discover that there exists an “effective move”, i.e., an unsettled situation where the next player to move would win the game. See Odd Cases 🤔 in the Japanese Rules - #2 by yebellz for further discussion.

Jigo and no result should not be conflated. With a jigo, one can view that sort of outcome as a tie. However, no result should not be viewed as a tie, but rather that a result has not yet been determined and the game should be restarted from an empty board in order to determine a result, if needed.

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Since reading this chapter I’ve been initiating more kos and even won a couple of games through ko. Two of his comments right at the beginning were particularly helpful:

  • Scoring a psychological triumph: I was always afraid to initiate ko since I did not understand how to fight it. It’s very encouraging to realize that the other player might be just as lost as me.

  • Gaining compensation elsewhere: It’s reassuring to think that I don’t have to win the ko to profit. My example below.

I gained no new insights about how to actually fight a ko from this chapter; that’s still a deep mystery. What order do you play your threats in, how carefully do you count them, etc.? But maybe that’s not critical for now.

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A principle I found useful: whenever I initiate the ko and/or play local ko threats, play preferably “outside” rather than “inside”, so that even if I lose the ko, at least the stones I’ve placed during the fight may become useful later.

  • get some experience on how to generate a ko
  • ko is the way to get your money back from playing (too?) solid.