-Edit - I got a bit confused with my diagrams in my first post so this is the correction version.
I have just started learning using the Interactive Way to Go website (it's so good!) and solve Tsumego on my phone, but the app I use doesn't really explain why a certain shape is the correct solution. Here is the problem from the Hactar Go Lite phone app.
White to play.
I finally arrive at the solution:
I'm guessing that White needs to stop Black from forming two eyes and living. So why is the above correct? Because I can see that Black has two eyes, one big one of the left and a small one on the right. Maybe I have completely misunderstood the point of this tsumego or the concept of forming eyes. Assuming that Black wants to form two eyes, could it then play either a or b? It looks okay to me.
[Hactar Go] Why is this tsumego solution correct?
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EdLee
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Hi Libcat,
B has only one real eye, and is dead.
(a) and (b) are two liberties, not two eyes.
(c) is a [sl=Falseeye]False Eye[/sl].
As an exercise, try to prove to your satisfaction that B cannot form two real eyes with this shape:
Did you mean to make 9x9 boards in your diagrams ?
... because your diagrams are open-ended on the right edge.
If your diagrams are supposed to be 9x9, then in your second diagram,
your
at J7, in reply to 
J9, is correct.
In the diagrams here, I made the boards bigger than 9x9,
and in reply to, W extends toward the right with 
.
B has only one real eye, and is dead.
(a) and (b) are two liberties, not two eyes.
(c) is a [sl=Falseeye]False Eye[/sl].
As an exercise, try to prove to your satisfaction that B cannot form two real eyes with this shape:
Did you mean to make 9x9 boards in your diagrams ?
... because your diagrams are open-ended on the right edge.
If your diagrams are supposed to be 9x9, then in your second diagram,
your
at J7, in reply to J9, is correct.In the diagrams here, I made the boards bigger than 9x9,
and in reply to
, W extends toward the right with .-
Kirby
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Re: [Hactar Go] Why is this tsumego solution correct?
The problem makes sense now, with the better diagrams. I removed your other thread, since it was confusing.
be immersed
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libcat
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Re:
@EdLee Hello and thank you!
Yes, I did not even realise this until checked my phone again. Here is the screenshot. It looks like everything was supposed to be happening on the top right of a 19x19 board, so technically yes, 9x9. I hadn't thought about this up till now, but clearly where the tsumego takes place/board size makes a huge difference! Sorry for missing that big detail.
I will have to check my understanding of all the concepts you linked to - especially false eyes since they don't look appear obvious to me.
ARGH okay yes, I see. Thanks again.
EdLee wrote:Did you mean to make 9x9 boards in your diagrams ?
... because your diagrams are open-ended on the right edge.
If your diagrams are supposed to be 9x9, then in your second diagram,
your
In the diagrams here, I made the boards bigger than 9x9,
and in reply to
Yes, I did not even realise this until checked my phone again. Here is the screenshot. It looks like everything was supposed to be happening on the top right of a 19x19 board, so technically yes, 9x9. I hadn't thought about this up till now, but clearly where the tsumego takes place/board size makes a huge difference! Sorry for missing that big detail.
I will have to check my understanding of all the concepts you linked to - especially false eyes since they don't look appear obvious to me.
EdLee wrote:As an exercise, try to prove to your satisfaction that B cannot form two real eyes with this shape:
ARGH okay yes, I see. Thanks again.
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libcat
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Re: [Hactar Go] Why is this tsumego solution correct?
Kirby wrote:The problem makes sense now, with the better diagrams. I removed your other thread, since it was confusing.
Thank you! (I don't know what the etiquette is here i.e, do I 'like' your reply? No idea, but either way I'm grateful)
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Joaz Banbeck
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Re: Re:
The easiest way to understand a false eye is to ask yourself how it will eventually resolve. ( Works for lots of other shapes too, FWIW )libcat wrote:... false eyes since they don't appear obvious to me.
If you look at the example used above...
you can realize that,sooner or later, ONE player must play BOTH of the circled points.
In other words, this:
...sharing of the two points cannot ever exist. Try it on a board to prove it to yourself.
Even if both players cooperate, you can't get there from here.
So, eventually it must end like this:
...or this:
BTW, I'm assuming in this post that you know basic dead/live shapes, and therefore you know that this:
..is dead.
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Joaz Banbeck
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Re: [Hactar Go] Why is this tsumego solution correct?
This is not the first time that the issue has been discussed.
For a slightly different statement of the issue, have a look at this: viewtopic.php?f=11&t=16767
For a slightly different statement of the issue, have a look at this: viewtopic.php?f=11&t=16767
Help make L19 more organized. Make an index: https://lifein19x19.com/viewtopic.php?f=14&t=5207