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 Post subject: Why is this tsumego solution correct?
Post #1 Posted: Thu Feb 13, 2020 11:59 am 
Lives with ko

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This is a beginners tsumego easy life from tsumego hero (66/200):

Click Here To Show Diagram Code
[go]$$Bc19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X . . , O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]



This solution is considered correct:

Click Here To Show Diagram Code
[go]$$Bc19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X 1 . . O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]


I can't see why.

Could not white always prevent black from forming 2 eyes by taking the point between the eyes however black captures,

Click Here To Show Diagram Code
[go]$$Bc19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X X X . O . X |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]


and if black does not capture there will be seki?

I'm sure I'm overlooking the solution (how this would be played out), but I've spent so much time on this, trying all moves I can see, it's driving me nuts.

Please tell me why/how this is supposed to work, thanks!

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 Post subject: Re: Why is this tsumego solution correct?
Post #2 Posted: Thu Feb 13, 2020 12:16 pm 
Lives in gote

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Seki is alive and the correct result :salute:

Click Here To Show Diagram Code
[go]$$Bc19 seki in sente
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X 1 . 2 O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]

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 Post subject: Re: Why is this tsumego solution correct?
Post #3 Posted: Thu Feb 13, 2020 12:34 pm 
Honinbo

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Click Here To Show Diagram Code
[go]$$Bc19 Gote life
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X 1 . . O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]


The solution diagram may show White making seki, but normally White will have a bigger play somewhere else. :)

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 Post subject: Re: Why is this tsumego solution correct?
Post #4 Posted: Thu Feb 13, 2020 2:21 pm 
Lives with ko

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There is sometimes a tacit cascade:
1) Find a solution to live with points
2) Find a solution to live with seki
3) Find a solution to live with ko where you take the ko first
4) Find a solution to live with ko where the opponent takes the ko first

If there is no solutions for 1) you have to find one for 2) and so on. Sometimes it will be stated like: black to live in ko. But sometimes it is not and you have to figure it out by yourself. The cascade doesn't end there. In theory, there are also multistep kos and probably some other special cases, but they are rather rare.

Of course there is also the reverse:
1) Find a solution that kills
2) Find a solution that kills with a ko that you take first
3) Find a solution that kills with a ko that your opponent takes first

Creating a seki is usually considered a loss for the attacker.

In the tsumego you posted, the book solution is best. All other moves will result in black's death. Or did you find a black move that lives with points?

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 Post subject: Re: Why is this tsumego solution correct?
Post #5 Posted: Thu Feb 13, 2020 2:36 pm 
Honinbo

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Seki is typically more valuable for the attacking player near the end of the game. That’s because, by getting seki, the attacking player prevents the living player from getting whatever points that eyespace would have been getting: usually less than 10 points. Moves early on are worth a lot more than that.

In contrast, killing a group without seki can sometimes be pretty profitable early on - the attacker will often get more than 20 points.

So for most of the game, seki is profitable for the defender, because they avoided death.

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 Post subject: Re: Why is this tsumego solution correct?
Post #6 Posted: Thu Feb 13, 2020 3:16 pm 
Gosei
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Click Here To Show Diagram Code
[go]$$Bc19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X 1 . a O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]


Black :b1: lives. What remains is an endgame play at A with value 3. Black can make 6 points with 1 move, White can neutralize it with 1 move, making seki.

Click Here To Show Diagram Code
[go]$$Bc19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X 2 . 1 O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]


Any other move by Black will fail. For example, this :b1: will be met with the throw-in of :w2:

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Post #7 Posted: Fri Feb 14, 2020 2:39 am 
Honinbo
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Hi Jika,
Jika wrote:
Click Here To Show Diagram Code
[go]$$B19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X X Y . O . B |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]
B killed itself in your var: either ( :bt: or :bc: ) = B dead.

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 Post subject: Re: Why is this tsumego solution correct?
Post #8 Posted: Fri Feb 14, 2020 12:59 pm 
Lives with ko

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Thank you for all your answers.

I think Ed gets closest to my question: I see black can only kill himself there. But how can black make two eyes (can he)?

On Tsumego Hero, this is from the most, most, first, easiest beginners easy life collection. Make two eyes, live.

For all the other "easy life" tsumego but this one so far I was able to figure out (not always read, but play out) where the living group would have 2 eyes.

Your answers look as if I have not overlooked a simple "there are your two eyes, dumb!" solution?

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 Post subject: Re: Why is this tsumego solution correct?
Post #9 Posted: Fri Feb 14, 2020 1:36 pm 
Lives in sente
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As explained by several people, if the two players play alternatively then Black cannot make two eyes, but can live in seki: after this position

Click Here To Show Diagram Code
[go]$$Bc19
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X X a O O O b |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]


no player can move in the area: if Black plays a or b then Black dies. If White plays at a then Black captures with b and can make two eyes. If White plays at b then Black captures with a and can make two eyes.

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 Post subject: Re: Why is this tsumego solution correct?
Post #10 Posted: Fri Feb 14, 2020 2:37 pm 
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Jika wrote:
On Tsumego Hero, this is from the most, most, first, easiest beginners easy life collection. Make two eyes, live.


And the next lesson is, make seki and live. :)

Looking at this question and others you have asked here, I think you would benefit from playing the Capture Game, where the first player to capture one or more stones wins. :)

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 Post subject: Re: Why is this tsumego solution correct?
Post #11 Posted: Fri Feb 14, 2020 3:22 pm 
Lives in sente

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bayu wrote:
There is sometimes a tacit cascade:
1) Find a solution to live with points
2) Find a solution to live with seki
3) Find a solution to live with ko where you take the ko first
4) Find a solution to live with ko where the opponent takes the ko first


We could add a fifth (place after 2) --- live in double ko

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Post #12 Posted: Fri Feb 14, 2020 4:42 pm 
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Hi Jika,
Quote:
But how can black make two eyes (can he)?

... Make two eyes, live.

... where the living group would have 2 eyes.
B cannot make 2 eyes here unless W helps B:
Click Here To Show Diagram Code
[go]$$B19 :w2: Pass
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . O O O O O O . |
$$ . . O . O X X X X X X |
$$ . , O X X 1 . 3 O O . |
$$ . . . O O X X X X X X |
$$ . . . . . O O O O O . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]
However, W can resist :b1: by taking :b3: , and B cannot make 2 eyes here.

As others have pointed out, the solution here is not to make 2 eyes, but to make seki. Just because all the other problems in your 'beginners' section so far have 2 eyes as the solution, it doesn't mean all the problems in the this section require you to "live with 2 eyes"; rather, they're teaching you to find 'the best' local solution, which, as mentioned, can mean seki, ko, etc. :tmbup:

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 Post subject: Re: Why is this tsumego solution correct?
Post #13 Posted: Sat Feb 15, 2020 5:13 am 
Lives with ko

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OK, I see.
So, either this tsumego is more advanced than the ones before and after it, so I misunderstood what it wanted me to do
(I came back to it several times before posting here, because I was able to pass those after that one by making two eyes)
or it may be consider "wrong" (in the sense that it "should not be so advanced in this collection" / "should not be in the midst of a collection of 'make 2 eyes' tsumego")
or just showing that, as there are multiple contributors to a collection, what one player calls "easy" is not "easy" beginners level for others.

Bill, I have Hactar Go light (plays the capture game) for Android.
I used to do well on it, but it has been a while since I used it.
When you say it may treat the root of the problem, I'll use it again for sure.

Thanks, Jika

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 Post subject: Re: Why is this tsumego solution correct?
Post #14 Posted: Sat Feb 15, 2020 7:49 am 
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Jika wrote:
OK, I see.
So, either this tsumego is more advanced than the ones before and after it, so I misunderstood what it wanted me to do
(I came back to it several times before posting here, because I was able to pass those after that one by making two eyes)
or it may be consider "wrong" (in the sense that it "should not be so advanced in this collection" / "should not be in the midst of a collection of 'make 2 eyes' tsumego")
or just showing that, as there are multiple contributors to a collection, what one player calls "easy" is not "easy" beginners level for others.


Well, yes, it is not easy to assign a level of difficulty to problems, and different people find different things difficult.

As for seki, a lot of people are unaware that it is a solution to a problem with the goal of making life. I suppose, then, that such problems are underrepresented among easy problems.

Quote:
Bill, I have Hactar Go light (plays the capture game) for Android.
I used to do well on it, but it has been a while since I used it.
When you say it may treat the root of the problem, I'll use it again for sure.


Do you play it on the 9x9? How well does it play? Can you beat it if you take White?

Good luck! :)

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At some point, doesn't thinking have to go on?
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 Post subject: Re: Why is this tsumego solution correct?
Post #15 Posted: Sat Feb 15, 2020 8:18 am 
Lives with ko

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Bill, just so I know we are talking about the same thing:

Do you mean the Capture Go game "whoever captures the other one first wins" (so, maybe b and w start with one stone each shoulder by shoulder and try capturing each other's stone before being captured themselves - so the board size does not matter that much as long as you have few stones in the beginning)?
(SL links to the Hactar App under this name of Capture Go - among other names - https://senseis.xmp.net/?AtariGo
, so I thought you must mean that one)

Or are we talking about this,
https://www.crazy-sensei.com/location=rules
(scroll down)
which, I think, you recommended to me and which would be great to train life and death too?

... Uhm, I think I remember we had this same discussion on the term "Capture Go" the last time and you are referring to the second one??? (Had loads of fun with that one, but on the 9x9 board it is only a 50:50 chance for me at the program's half strength and me playing black!!!)

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 Post subject: Re: Why is this tsumego solution correct?
Post #16 Posted: Sat Feb 15, 2020 9:30 am 
Honinbo

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There are different varieties of Capture Go. The only ones I know of have the winning condition that the first player to capture some given number of stones wins. Usually you only have to capture one stone to win, but Capture-2, etc., are also played. The more stones you have to capture the closer the game resembles regular go. :)

My own preference is for the one that starts on an empty board, with no passes, no suicide, and you can also win if your opponent has no legal play.

Anyway, Capture Go teaches players about counting liberties and also about seki. But with Capture-1 you can have a seki that might be dead under Capture-4, because you can kill if you can sacrifice three stones. ;)

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