Life In 19x19

Hi,
I saw in book an invasion that went like that :

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[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . 8 7 9 . . . |
$$ . . . 2 1 5 c . |
$$ . . . B 3 B b . |
$$ . . . a 4 6 . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

Then they talk about continuation for at "a" and "b", but nothing is said about at "c"
Trying for my self I went to this where white lives...
Is my sequence correct ? Is there anything better for black (or for white) ?

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[go]$$B
$$ ----------------+
$$ . . 9 7 0 5 6 . |
$$ . . X O O 8 2 4 |
$$ . . . X O O 1 . |
$$ . . . B O B 3 . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

Any thought is welcome...

You have found the sequence which invalidates a black move at c

oca wrote:...

$$B
$$ ----------------+
$$ . . 9 7 0 5 6 . |
$$ . . X O O 8 2 4 |
$$ . . . X O O 1 . |
$$ . . . B O B 3 . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |

Click Here To Show Diagram Code

[go]$$B
$$ ----------------+
$$ . . 9 7 0 5 6 . |
$$ . . X O O 8 2 4 |
$$ . . . X O O 1 . |
$$ . . . B O B 3 . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

...

Black can start a ko like this. It is not easy for black to win because of his cutting points, but white has to win to live.

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[go]$$B
$$ ----------------+
$$ . . . . 0 . . . |
$$ . . X O O . 2 3 |
$$ . . . X O O 1 . |
$$ . . . X O X 4 5 |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

I don't think that this ko is even worth considering this early in the game as there is almost certain no threat big enough. Later in the game it may be a possibility.

DrStraw wrote:I don't think that this ko is even worth considering this early in the game as there is almost certain no threat big enough. Later in the game it may be a possibility.

Agreed. So black probably tenukis at 3, and gets sente.

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[go]$$B
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . 2 . |
$$ . . . X O O 1 . |
$$ . . . X O X . . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

Later, if white wants to repair it, he loses sente again:

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[go]$$Wm96
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . O . |
$$ . . . X O O X 3 |
$$ . . . X O X 1 . |
$$ . . . . X X 2 . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

So black can leave it until he has good ko theats, and until he does, it is always going to be a pile of bad aji for white.

Thanks, that's very interesting, variants with ko never comes into my mind...

oca, as you showed with your sequence connecting with 3 doesn't kill the corner. But even if it did (locally) you need to realize there is a big weakness in black's surrounding position with this cut of 4.

Click Here To Show Diagram Code

[go]$$B
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . 2 . |
$$ . . 4 X O O 1 . |
$$ . . . B O B 3 . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

If white captures part of black's wall he lives easily and escapes and destroys black's outside influence. Now it may be that black just about manages to keep everything together but at a minimum it means the ko Joaz showed is utterly unplayable for black as white has loads of local threats. That's why the book recommended connecting at a (now the cut of 4 above can be captured in a ladder, or if no ladder the fight is now much easier for black). It's a very common beginner (and not beginner!) mistake to only look at the opponent's problems and try to kill something, only for them to counterattack and exploit your weaknesses you overlooked and kill some of you instead.

Joaz Banbeck wrote:
Later, if white wants to repair it, he loses sente again:

$$Wm96
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . O . |
$$ . . . X O O X 3 |
$$ . . . X O X 1 . |
$$ . . . a X X 2 . |
$$ . . . . . . . . |
$$ . . . . . . . . |

Click Here To Show Diagram Code

[go]$$Wm96
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . O . |
$$ . . . X O O X 3 |
$$ . . . X O X 1 . |
$$ . . . a X X 2 . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

Actually white can tennuki after black 97 and he has elimnated in the ko in sente already (though at the cost of making a bad exchange as if black then captures the stone and white answers that capture made him stronger). If black doesn't want white to fix in sente he has to tenuki 96 but then if white crawls at 97 it takes a liberty and the cut at a becomes very serious.

Uberdude wrote:oca, as you showed with your sequence connecting with 3 doesn't kill the corner. But even if it did (locally) you need to realize there is a big weakness in black's surrounding position with this cut of 4.

$$B
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . 2 . |
$$ . . 4 X O O 1 . |
$$ . . . B O B 3 . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |

Click Here To Show Diagram Code

[go]$$B
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . 2 . |
$$ . . 4 X O O 1 . |
$$ . . . B O B 3 . |
$$ . . . . X X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

If white captures part of black's wall he lives easily and escapes and destroys black's outside influence. Now it may be that black just about manages to keep everything together but at a minimum it means the ko Joaz showed is utterly unplayable for black as white has loads of local threats. That's why the book recommended connecting at a (now the cut of 4 above can be captured in a ladder, or if no ladder the fight is now much easier for black). It's a very common beginner (and not beginner!) mistake to only look at the opponent's problems and try to kill something, only for them to counterattack and exploit your weaknesses you overlooked and kill some of you instead.

Wow ... the ladder doesn't work... back to "Lessons In The Fundamentals Of Go" Chapter 1 ...

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[go]$$B
$$ ----------------+
$$ . . . . . . . . |
$$ . . X O O . . . |
$$ . X . X O O a . |
$$ . . . X O X . . |
$$ . . . X X X . . |
$$ . . . . . . . . |[/go]

Suppose B manages to eliminate all outside weaknesses. Playing "a" would still be the wrong -- B has a better attack.

Something like that ? seki I think...

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[go]$$B
$$ --------------------+
$$ . . . . 9 6 . 7 5 . |
$$ . . . . X O O 0 1 8 |
$$ . . . X . X O O 2 4 |
$$ , . . . . X O X 3 . |
$$ . . . . . X X X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |[/go]

oca wrote:Something like that ? seki I think...

$$B
$$ --------------------+
$$ . . . . 9 6 . 7 5 . |
$$ . . . . X O O 0 1 8 |
$$ . . . X . X O O 2 4 |
$$ , . . . . X O X 3 . |
$$ . . . . . X X X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |

Click Here To Show Diagram Code

[go]$$B
$$ --------------------+
$$ . . . . 9 6 . 7 5 . |
$$ . . . . X O O 0 1 8 |
$$ . . . X . X O O 2 4 |
$$ , . . . . X O X 3 . |
$$ . . . . . X X X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |[/go]

9 at 10 creates a bulky 5, which is dead.

oca wrote:Something like that ? seki I think...

$$B
$$ --------------------+
$$ . . . . 9 6 . 7 5 . |
$$ . . . . X O O 0 1 8 |
$$ . . . X . X O O 2 4 |
$$ , . . . . X O X 3 . |
$$ . . . . . X X X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |

Click Here To Show Diagram Code

[go]$$B
$$ --------------------+
$$ . . . . 9 6 . 7 5 . |
$$ . . . . X O O 0 1 8 |
$$ . . . X . X O O 2 4 |
$$ , . . . . X O X 3 . |
$$ . . . . . X X X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |[/go]

is fine. It is not seki but w is dead. is worse than a pass! It looses sente, it costs 1 pt and you destroy about 4 liberties of your dead group. Making it much deader, so to speak.

edit: Ofcourse Joaz is right. is unnecessary most of the times.

cyclops wrote: ...
is fine. It is not seki but w is dead.

is useful only if white has stones around M18 or M19 and is threatening to connect out, or if there is a liberties race - in which case T16 must be played, followed by T19, and the throwin at S19.

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[go]$$Bc
$$ --------------------+
$$ . . . . 9 6 . 7 5 . |
$$ . . . . X O O 0 1 8 |
$$ . . . X . X O O 2 4 |
$$ , . . . . X O X 3 B |
$$ . . . . . X X X . . |
$$ . . . . . . . . . . |
$$ . . . . . . . . . . |[/go]

edit: off topic, deleted