To confuse you even further: things are clear when a group consists of only one string. In the diagram below, "a" and "b" are eyes because they are adjacent to the black string, and only to it.
When there are two strings:
"a" and "b" are eyes because each of them is adjacent to each black string and only to them.
A group can have two eyes that look like false eyes:
https://senseis.xmp.net/?TwoHeadedDragon
There are two eyes because the black group consists two strings, and "a" and "b" are empty intersections which are adjacent to each of these two strings and only to them.
On the other hand, in the original diagram there are three strings
but Black cannot play immediately at "a" so we can suppose that "a" is white, so we get two strings
The eye "b" is adjacent to only one string, so the group doesn't have two eyes. Another way of seeing this is to fill external liberties with enemy stones
and see that the lower white group is in atari.
(All the above is pretty obvious for experienced players, however it is not uncommon for SDKs to confuse false eyes with real eyes during a game... including me...)
Why is white dead? II
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Pio2001
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Re:
The idea is not mineEdLee wrote:I like how Pio merged sensei's two separate cases "on the side" and "at the corner" into one "by the 2nd line", but it's still nice to include both a side diagram and a corner diagram
It comes from the book Level Up! volume 4 (Lee Jae-Hwan, Yoo Chang-Hyuk).
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Joaz Banbeck
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Re: Why is white dead? II
There are two ideas mentioned above which I think are even better if explicitly placed together:
...and this:
...and this:
Once the string of black stones is completely surrounded, black can either save it by filling in his 'eye', or white can take it, in which case if becomes a ko. And it is a ko that - as demonstrated earlier in this thread - black cannot win.
Pio2001 wrote:...
There are only three kind of false eyes.
The false eye by the large diagonal :
The false eye by the one point jump :
And the false eye by the second line :
...
If you use jlt's idea of filling liberties on Pio's diagrams, they look like this:jlt wrote:... Another way of seeing this is to fill external liberties with enemy stones
and see that the lower white group is in atari...
...and this:
...and this:
Once the string of black stones is completely surrounded, black can either save it by filling in his 'eye', or white can take it, in which case if becomes a ko. And it is a ko that - as demonstrated earlier in this thread - black cannot win.
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