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 Post subject: Re: Which is bigger, A or B? #61 Posted: Mon Mar 20, 2017 7:40 am
 Judan

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Uberdude wrote:
Kirby, if you have doubts about the one space jump after ignored hane being sente, why do you think push after your descent is sente?

Well, the two are similar in that regard. What's most unclear to me is the throw-in variation with the ko. If black has ko threats, practically speaking, it seems black may be able to block at 'y' in sente.

But I guess I think it's more likely that white lives in sente since black has to eventually take the ko.

I guess I lean toward thinking the hane is better than descending, but I can't say I have my head wrapped around the position.

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 Post subject: Re: Which is bigger, A or B? #62 Posted: Mon Mar 20, 2017 8:36 am
 Oza

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Kirby wrote:
Uberdude wrote:
Kirby, if you have doubts about the one space jump after ignored hane being sente, why do you think push after your descent is sente?

Well, the two are similar in that regard. What's most unclear to me is the throw-in variation with the ko. If black has ko threats, practically speaking, it seems black may be able to block at 'y' in sente.

But I guess I think it's more likely that white lives in sente since black has to eventually take the ko.

I guess I lean toward thinking the hane is better than descending, but I can't say I have my head wrapped around the position.

Hmmmm, you still seem to be confused. So if white hanes then if black blocks directly white is still not alive (a17 still kills, the exchange didn't help white):

`[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 to be consistent with the first move white would connect and live. This leaves a 1st line cut of some fairly large endgame value that black may or not defend with his sente (probably not in this game).
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . . 3 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]`

If white hanes and black throws in then white takes. White is now alive, the throw in helped white live as a17 no longer kills.
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . 3 2 1 y . . . . . . . . . . . . . . |\$\$ | . 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]`

Black now has sente, but white is already alive. Black could choose to place a stone at y (which he already had if he didn't throw in!) and it looks like below.
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . 3 . 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]`

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.
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . O . O X . . . . . . . . . . . . . . |\$\$ | . O O X X . . . . . . . . . . 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]`

So if you want to compare with the descend, you need to compare with a white living in gote variation in which black didn't help white live, so:
`[go]\$\$Wc White lives in gote with hane\$\$ +---------------------------------------+\$\$ | . . 3 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]`

vs:
`[go]\$\$Wc White lives in gote with descend\$\$ +---------------------------------------+\$\$ | . . 1 . . . . . . . . . . . . . . . . |\$\$ | . 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 the first white's endgame follow up is cutting and taking a load of points, let's say black plays 2 to stop white breaking in there:
`[go]\$\$Wc follow-up after hane\$\$ +---------------------------------------+\$\$ | . . O O X 3 7 5 6 . . . . . . . . . . |\$\$ | . O O X 1 . . 4 8 . . . . . . X X O . |\$\$ | . X O X 2 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]`

vs the smaller reduction:
`[go]\$\$Wc follow-up after descend\$\$ +---------------------------------------+\$\$ | . . O 1 3 4 . . . . . . . . . . . . . |\$\$ | . O O X 2 . . . . . . . . . . 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]`

 This post by Uberdude was liked by: Bill Spight
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 Post subject: Re: Which is bigger, A or B? #63 Posted: Mon Mar 20, 2017 9:19 am
 Judan

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Just to follow up a bit on Uberdude's analylis.

`[go]\$\$Wc White gote\$\$ +---------------------------------------+\$\$ | . . 3 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]`

Globally, we agree that Black plays tenuki now, rather than let White live with sente. Let's do a little tewari.

`[go]\$\$Wc Sagari with White sente follow-up\$\$ +---------------------------------------+\$\$ | . . 1 3 . . . . . . . . . . . . . . . |\$\$ | . O O X 4 . . . . . . . . . . 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]`

If White lives with the sagari and later takes his local sente with , is obviously correct.

`[go]\$\$Wc Variation\$\$ +---------------------------------------+\$\$ | . . 1 3 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]`

is incorrect. But it duplicates the position in the first diagram, which indicates that in that diagram is wrong.

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 Post subject: Re: Which is bigger, A or B? #64 Posted: Mon Mar 20, 2017 10:03 am
 Judan

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Uberdude wrote:
Hmmmm, you still seem to be confused.

Oh, I don't doubt it!

Actually, though, your analysis mostly makes sense, but what hangs me up is this (bold part added by me):

Uberdude wrote:
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . 3 . 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]`

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.
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . O . O X . . . . . . . . . . . . . . |\$\$ | . O O X B . . . . . . . . . . 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]`

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.

So it's not as straightforward to me as a position that is 100% gote for black.

That's why the descent is much easier for me to understand:

`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . . 1 3 5 6 . . . . . . . . . . . . . |\$\$ | . O O X 4 . . . . . . . . . . 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]`

Black clearly ends in gote, so I can see the end result.

But here:
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . O . O X . . . . . . . . . . . . . . |\$\$ | . O O X C . . . . . . . . . . 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]`

Is the marked intersection necessary? It's not as clear to me.

So if we assume that black must defend this spot and gets gote, then I can compare it apples-to-apples with the descent variation where I know black gets gote.

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.

In practice, the ko is probably too heavy on black, so it's basically as good as black having gote.

But it just bugs me a little bit that it seems like it could be sente.

I guess I just have to accept that black cannot afford to take sente in this situation, and if I treat that as an absolute, then we can say that white absolutely lives in sente if black does the throw-in.

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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 Post subject: Re: Which is bigger, A or B? #65 Posted: Mon Mar 20, 2017 10:46 am
 Oza

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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.

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

`[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]`

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 Post subject: Re: Which is bigger, A or B? #66 Posted: Mon Mar 20, 2017 11:48 am
 Judan

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

`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . 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.

`[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.

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 Post subject: Re: Which is bigger, A or B? #67 Posted: Mon Mar 20, 2017 12:42 pm
 Judan

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Kirby wrote:
but what hangs me up is this (bold part added by me):
Uberdude wrote:
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . 3 . 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]`

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.
`[go]\$\$Wc \$\$ +---------------------------------------+\$\$ | . O . O X . . . . . . . . . . . . . . |\$\$ | . O O X B . . . . . . . . . . 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]`

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.

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.

`[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.

`[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.

`[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.

`[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.

Kirby wrote:
And in that case, I guess doing the throw-in is not a good move, and not a variation we should compare.

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.

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 Post subject: Re: Which is bigger, A or B? #68 Posted: Mon Mar 20, 2017 1:07 pm
 Judan

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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.

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