If black plays the throw-in he doesn't block in sente, but in gote! Black plays the last move, 4, below.

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[go]$$Wc Black takes gote, white already alive
$$ +---------------------------------------+
$$ | . 3 2 1 4 . . . . . . . . . . . . . . |
$$ | . O O X . . . . . . . . . . . X X O . |
$$ | . X O X . X . . . . . . . . X . X O . |
$$ | . O X , . . . . . , . X . . . X O . . |
$$ | . O X . . . . . . . . . . . . X O O . |
$$ | . X X X . . . . . . . . . O X O X X . |
$$ | . . O X . . . . . . . . . . O O O . . |[/go]

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.

In the case of the descent, black blocking off the top is gote, but has no sente follow-up.

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[go]$$Wc
$$ +---------------------------------------+
$$ | . . 1 2 . . . . . . . . . . . . . . . |
$$ | . O O X . . . . . . . . . . . X X O . |
$$ | . X O X . X . . . . . . . . X . X O . |
$$ | . O X , . . . . . , . X . . . X O . . |
$$ | . O X . . . . . . . . . . . . X O O . |
$$ | . X X X . . . . . . . . . O X O X X . |
$$ | . . O X . . . . . . . . . . O O O . . |[/go]

So it seems close to a 1-to-1 comparison, but doesn't seem exactly the same to me.

_________________
be immersed

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.

Let's look at a sente ko that I think is clear to you.

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[go]$$Bc Black sente ko
$$ +---------------------------------------+
$$ | . O 1 O X . . . . . . . . . . . . . . |
$$ | . O O X . . . . . . . . . . . X X O . |
$$ | 2 X O X . X . . . . . . . . X . X O . |
$$ | . O X , . . . . . , . X . . . X O . . |
$$ | . O X . . . . . . . . . . . . X O O . |
$$ | . X X X . . . . . . . . . O X O X X . |
$$ | . . O X . . . . . . . . . . O O O . . |[/go]

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.

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[go]$$Wc White sente ko
$$ +---------------------------------------+
$$ | . O X 1 X . . . . . . . . . . . . . . |
$$ | . O O X 2 . . . . . . . . . . X X O . |
$$ | O . O X . X . . . . . . . . X . X O . |
$$ | . O X , . . . . . , . X . . . X O . . |
$$ | . O X . . . . . . . . . . . . X O O . |
$$ | . X X X . . . . . . . . . O X O X X . |
$$ | . . O X . . . . . . . . . . O O O . . |[/go]

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.

Click Here To Show Diagram Code

[go]$$Wc White sente
$$ +---------------------------------------+
$$ | . O 1 O X . . . . . . . . . . . . . . |
$$ | . O O X 2 . . . . . . . . . . X X O . |
$$ | O . O X . X . . . . . . . . X . X O . |
$$ | . O X , . . . . . , . X . . . X O . . |
$$ | . O X . . . . . . . . . . . . X O O . |
$$ | . X X X . . . . . . . . . O X O X X . |
$$ | . . O X . . . . . . . . . . O O O . . |[/go]

In this position White could simply fill the ko at with sente. But that is not the real threat.

Click Here To Show Diagram Code

[go]$$Wc White makes a large ko
$$ +---------------------------------------+
$$ | . O . O X . . . . . . . . . . . . . . |
$$ | . O O X 1 . . . . . . . . . . X X O . |
$$ | O . O X . X . . . . . . . . X . X O . |
$$ | . O X , . . . . . , . X . . . X O . . |
$$ | . O X . . . . . . . . . . . . X O O . |
$$ | . X X X . . . . . . . . . O X O X X . |
$$ | . . O X . . . . . . . . . . O O O . . |[/go]

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.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

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.

_________________
be immersed