newbie question about life and death

[demigod]

Hey everyone, I am a big time newbie.
Reading the "All about life and death book" as my first.
Here is a common problem covered in the very beginning.
Can someone explain me how white "b" is good enough? Why is place stone right under "b" bad?
Thanks.

[p2501]

edit: obselete

[demigod]

I don't quite get it: can white capture the black group here?
The way I see it white go 1, then black 2, white 3, black 4 and the black group will connect nevertheless.
What am I missing?
What if there were no K3 stone?

[HermanHiddema]

$$W setup
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . . O X X X X X |
$$ . . . . 4 1 2 . 3 . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$W setup
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . . O X X X X X |
$$ . . . . 4 1 2 . 3 . |
$$ --------------------+[/go]

The place under b is bad because it leads to ko:

$$W ko
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . 6 O X X X X X |
$$ . . . 5 X a X . O . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$W ko
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . 6 O X X X X X |
$$ . . . 5 X a X . O . |
$$ --------------------+[/go]

Now captures at a, then black can fight the ko to connect.

$$W kill
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X b 5 O X X X X X |
$$ . . 7 6 X a X . O . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$W kill
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X b 5 O X X X X X |
$$ . . 7 6 X a X . O . |
$$ --------------------+[/go]

But if white plays b, then black cannot escape. After white can either capture at a, or connect at b.

[Bill Spight]

Just presenting things another way.

(;AP[GOWrite:2.2.21]SZ[19]FF[4]GM[1]CA[ISO8859-1]ST[2]PB[ ]PW[ ]GN[ ]PM[2]FG[259:]AW[nr][nq][ro][pq][oq][qq][rq]AB[jq][or][qr][pr][sr][rr][kr]
(
;W[os]C[*** There is death in the hane.]
;B[ps]
;W[rs]C[*** The key point to hold Black to one eye. Black is dead.]
;B[ns]C[*** Escape attempt.]
(
;W[mr]C[*** White contains Black.]
;B[ms]C[*** One more try.]
;W[ls]C[*** Atari on two stones.]
(
;B[os]
;W[lr]C[*** The escape attempt fails.]
)
(
;B[lr]
;W[os]
)

)
(
;W[ms]C[*** Not so good.]
;B[mr]C[*** Black makes ko.]
;W[os]
)

)
(
;W[rs]C[*** Mistake.]
;B[os]
;W[qs]C[*** Black has only one eye in the corner.]
;B[ns]
;W[mr]
;B[ms]
(
;W[lr]
;B[ls]C[*** But Black escapes.]
)
(
;W[ls]C[*** Futile.]
;B[lr]
)

)

)

And welcome to go!

[p2501]

maybe I should have read the text >.<

[demigod]

Thanks guys, I got how white can capture black by going b.

What i don't get is how black connects via ko: here white takes the stone (playing at a) and next stone disables any escape attempts by placing white stone between 5 and a.

$$W ko
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . 6 O X X X X X |
$$ . . . 5 X a X . O . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$W ko
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . 6 O X X X X X |
$$ . . . 5 X a X . O . |
$$ --------------------+[/go]

[skydyr]

Thanks guys, I got how white can capture black by going b.

What i don't get is how black connects via ko: here white takes the stone (playing at a) and next stone disables any escape attempts by placing white stone between 5 and a.

$$W ko
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . 6 O X X X X X |
$$ . . . 5 X a X . O . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$W ko
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |
$$ , . . . . . . . . . |
$$ X . . . O O O O O O |
$$ . X . 6 O X X X X X |
$$ . . . 5 X a X . O . |
$$ --------------------+[/go]

Well, it's a ko, so black can't take the white stone back immediately. However, he can play a big threatening move somewhere else, and white has to decide: Do I make sure the corner is dead, or do I need to respond to black's move? If white thinks the corner is bigger than black's follow up, he'll kill the corner as you suggest, but then black gets the other move in the other area as compensation, to offset the loss. If white thinks that other move is bigger, he defends, but then black can take the ko and white has to find a big threat. The corner looks to be worth around 22 points, so you can count how much the threats look to be worth and evaluate what white should do based on that.

[demigod]

thanks, got it =)

[xed_over]

thanks, got it =)

great question. thanks for asking.