If black plays the throw-in he doesn't block in sente, but in gote! Black plays the last move, 4, below.Kirby wrote:
Since it seems theoretically possible for black to block off in sente here due to an unknown ko situation, it's hard for me to feel completely satisfied.
Which is bigger, A or B?
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Uberdude
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Re: Which is bigger, A or B?
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Kirby
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Re: Which is bigger, A or B?
In that case, white does get sente for a move, but capturing the stone is sente. So it's gote with a sente follow-up - which also depends on the ko, so it's still a bit confusing to me.Uberdude wrote: If black plays the throw-in he doesn't block in sente, but in gote! Black plays the last move, 4, below.
In the case of the descent, black blocking off the top is gote, but has no sente follow-up.
So it seems close to a 1-to-1 comparison, but doesn't seem exactly the same to me.
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Bill Spight
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Re: Which is bigger, A or B?
IMX, sente ko is not textbook material. You can see it in pro games, and infer it from some of the textbook lines of play, but I think that most good players just pick up the idea, as I did.Kirby wrote:but what hangs me up is this (bold part added by me):Since the ko situation is not clear to me, it's not clear to me that black has to defend at the marked stone in the position above.Uberdude wrote: Usually black doesn't need to worry much about the ko cut, because taking the ko is sente for him to kill the corner, so it likely ends up looking like this after he takes the ko and later white takes back and black defends. So black closed the top, but took gote to do it. It's like you decided to defend the cutting point after diagram 2, but maybe another move is bigger.
Let's look at a sente ko that I think is clear to you.
threatens the sagari at 2, killing the White group. Yes, White could fight the ko, but to do so White needs some large threats, while Black does not. In nearly all cases White will have to live with 
, sooner or later. I think that we can all agree that this diagram shows the normal result in the corner. 
Now let's look at another sente ko.
This is a form of a bread and butter sente ko that occurs frequently in pro and, I dare say, amateur games. I don't mean this particular formation, but one where one player takes the ko on the edge and the other player protects against the second line cut. By comparison with this position,
gains 1 2/3 points, on average. So this is a 1 2/3 pt. sente ko. In this position White could simply fill the ko at
with sente. But that is not the real threat.The real threat is the cut at
, which makes a large ko. Yes, Black takes the ko first, but if Black wins the ko he gains only 3 points by comparison with the previous position. That means that White only needs ko threats that gain more than 3 points to make a good proposition, on average. White does not need to win the large ko. OTOH, Black needs large threats, either to win it or to give it up. Again, the necessity of large ko threats for one player but not the other is what makes this a sente ko. Sure, it is possible for that player for to have those large threats, but the normal result is for the ko to be taken in sente. Now, the 1 2/3 pt. sente ko is often fought, because it is so small, and often the disparity in the size of threats is not very large, but in both of these examples the defender needs really large threats to fight the ko.
Oh, the throw-in per se is not bad. In fact, it would be possible to construct whole board positions where it is the only play. The problem comes with the next play, if Black does not tenuki. Then he has allowed White to live in sente, which is almost surely bad -- very bad with this whole board position, in fact.Kirby wrote:And in that case, I guess doing the throw-in is not a good move, and not a variation we should compare.
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Re: Which is bigger, A or B?
I guess since both white and black both have sente ko, it is safe to assume that the throw-in followed by the block at 'y' is gote for black, even though there is a sente ko follow-up. Because to be fair, white also has sente ko after that for which black had to defend.
Maybe the exception is if one player could be known to have the upper hand in the kos.
Maybe the exception is if one player could be known to have the upper hand in the kos.
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