7k tsumego from a Japanese tsumego book

[tchan001]

$$Bc
$$ ----------------+
$$ . . . . . . . . |
$$ . O O X . X . . |
$$ . . . O . X X . |
$$ . . O . O X O . |
$$ . . . . O O O . |
$$ . . . . . . . . |
$$ . . . . . . . . |

Click Here To Show Diagram Code

[go]$$Bc
$$ ----------------+
$$ . . . . . . . . |
$$ . O O X . X . . |
$$ . . . O . X X . |
$$ . . O . O X O . |
$$ . . . . O O O . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

Black to move
What is the status of the black group given the optimal sequence of play?

[RBerenguel]

I see ways for white to kill, but there can always be traps I can't read... I am pretty sure black can kill easily

[tj86430]

I didn't find a way for black to live.

[karaklis]

Nice problem.

I cannot see that w can do anything after b p19. If w tries to make ko or seki, then this happens:

$$Bc
$$ ----------------+
$$ . . . 1 . 7 4 . |
$$ . O O X 6 X 5 2 |
$$ . . . O . X X 3 |
$$ . . O . O X O . |
$$ . . . . O O O . |
$$ . . . . . . . . |
$$ . . . . . . . . |

Click Here To Show Diagram Code

[go]$$Bc
$$ ----------------+
$$ . . . 1 . 7 4 . |
$$ . O O X 6 X 5 2 |
$$ . . . O . X X 3 |
$$ . . O . O X O . |
$$ . . . . O O O . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

Black lives by oshitsubushi

$$Bc
$$ ----------------+
$$ . . . 1 7 6 4 . |
$$ . O O X . X 5 2 |
$$ . . . O . X X 3 |
$$ . . O . O X O . |
$$ . . . . O O O . |
$$ . . . . . . . . |
$$ . . . . . . . . |

Click Here To Show Diagram Code

[go]$$Bc
$$ ----------------+
$$ . . . 1 7 6 4 . |
$$ . O O X . X 5 2 |
$$ . . . O . X X 3 |
$$ . . O . O X O . |
$$ . . . . O O O . |
$$ . . . . . . . . |
$$ . . . . . . . . |[/go]

again oshitsubushi


Well, obviously I got it wrong. Never mind.

[Wildclaw]

What is the status of the black group given the optimal sequence of play?

I am a bit out of shape, but I think the optimal sequence goes like this.

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

Click Here To Show Diagram Code

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

1. Standard way to live with this shape by expanding eye space
2. Key move aiming to remove the Q18 eye
3. Only way for black to protect
4. But now white has time to throw in
5-7. Black has no choice but to capture
8-0. Giving white the opportunity to fill all the outside liberties.

[tchan001]

Good job Wildclaw. Actually the book solution ends with 3 and says something about Black living (althought it doesn't have the word seki anywhere in the explanation), but the sequence you have is the one I arrived at as well.

[Bill Spight]

What is the status of the black group given the optimal sequence of play?

I am a bit out of shape, but I think the optimal sequence goes like this.

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

Click Here To Show Diagram Code

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

1. Standard way to live with this shape by expanding eye space
2. Key move aiming to remove the Q18 eye
3. Only way for black to protect
4. But now white has time to throw in
5-7. Black has no choice but to capture
8-0. Giving white the opportunity to fill all the outside liberties.

White can usually omit , as it is gote. He can also probably save as a potential ko threat.