Life In 19x19

jumapari wrote:In his book Richard Hunter speaks about "weak eyes". [...]
Is there any theory about this?

See https://www.lifein19x19.com/viewtopic.p ... 67#p257667

RobertJasiek wrote:

jumapari wrote:In his book Richard Hunter speaks about "weak eyes". [...]
Is there any theory about this?

See https://www.lifein19x19.com/viewtopic.p ... 67#p257667

Thank you! Next time I'll read your comments with more attention

Reading often implies not only the iteration of possible move candidates, but also pruning out branches where the end state is already known. Everybody does this.

One example that comes to mind is a heuristic I heard that says, "in life and death problems, if one side captures 3 stones, they get an eye for that capture". I think this isn't 100% true, but it's true very often. So it means that while I'm doing life and death problems, except for those exceptional cases, I can treat the capture of >= 3 stones as an eye - and I don't have to read out the actual formation of an eye. It speeds things up a little bit, and I can come to recognize exceptions to this rule and revisit as necessary.

Anyway, rules like this help with pruning, which is something that good readers do all of the time - either explicitly or by experience.

But it's important to understand the nuances of things so that when those pruning heuristics aren't applicable, you don't accidentally apply them.

jumapari wrote:In his book Richard Hunter speaks about "weak eyes". Eyes that have less liberties as it seems, but there is not so much explanation about this. As far as I can see those eyes are mainly in the corner, where its most easy for the attacker of the eye to create a eye within the eye.
Is there any theory about this?
Thanks!

Depends on what you mean by theory. A theory can be a set of facts, i.e., an explicit theory. It can be, and usually is, an implicit theory, i.e, a description of those facts. I think that the explicit theory of weak eyes is complete. That is, every weak eye with the relevant play has been recorded somewhere. As for the implicit theory, what Hunter said is an implicit theory of weak eyes.

BTW, there are eyes that have fewer liberties than they appear to have that are not weak eyes. They are called big eyes. That's not exactly what Hunter said. There is a formula for counting the liberties of big eyes. But there are some big eyes where the formula is wrong. It gives too many liberties. The reason, as Hunter indicates, is that the opponent may make an eye inside the big eye or threaten to do so. Even if correct, that implicit theory is not much help without some of the explicit theory as a guide.

Fortunately, Sensei's Library provides some of the explicit theory on this page. https://senseis.xmp.net/?BigEyesCanBeSmallInTheCorner

Kirby wrote:Reading often implies not only the iteration of possible move candidates, but also pruning out branches where the end state is already known. Everybody does this.

One example that comes to mind is a heuristic I heard that says, "in life and death problems, if one side captures 3 stones, they get an eye for that capture". I think this isn't 100% true, but it's true very often.

One result of capturing three connected stones.

Click Here To Show Diagram Code

[go]$$W One eye
$$ --------------
$$ . X C C C X .
$$ . O X X X X .
$$ . O O O O X .
$$ . . . . . . .[/go]

Click Here To Show Diagram Code

[go]$$W One eye
$$ --------------
$$ . X 1 2 C X .
$$ . O X X X X .
$$ . O O O O X .
$$ . . . . . . .[/go]

If , makes an eye at .

Another result of capturing three connected stones.

Click Here To Show Diagram Code

[go]$$B No eye
$$ -----------------
$$ . X X C C C X X .
$$ . . O X X X O . .
$$ . . O O O O O . .
$$ . . . . . . . . .[/go]

Click Here To Show Diagram Code

[go]$$B No eye
$$ -----------------
$$ . X X 1 . 2 X X .
$$ . . O X X X O . .
$$ . . O O O O O . .
$$ . . . . . . . . .[/go]

If , prevents an eye, except a defective or "false" eye.

(N.B. There are rare cases where the defective eye produced by capturing will make life.)

Yeah, this kind of nuance shows that the heuristic doesn't always work. It helps with pruning in many cases, but you need to know when it doesn't.

Bill Spight wrote:
Fortunately, Sensei's Library provides some of the explicit theory on this page. https://senseis.xmp.net/?BigEyesCanBeSmallInTheCorner

Thanks a lot! Exactly that what I was looking for!