the following problem is problem #42 in the Just Go life and death training.

I think Black should be trying to prevent the eye that A2 and B1 can form. But I cant figure this one out.

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I will try to give the smallest possible hint about how to approach this.

With situations like these you generally have two ways to kill:

• Capture White before they capture you
• Make a bulky shape that when captured is only one eye

In a good problem, both techniques may be necessary depending on what White does.

Click Here To Show Diagram Code

[go]$$B
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . , . , . . |
$$ | . . . . . . . . . |
$$ | X X X X X X , . . |
$$ | O O O O O X . . . |
$$ | M Z Z O X X , . . |
$$ | M Z O O O X . . . |
$$ | . . O . X . . . . |
$$ +-------------------+[/go]

/ is a dead eye-shape.

Click Here To Show Diagram Code

[go]$$B
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . , . , . . |
$$ | . . . . . . . . . |
$$ | X X X X X X , . . |
$$ | W W W W W X . . . |
$$ | ? X X W X X , . . |
$$ | . X W W W X . . . |
$$ | . ? W ? X . . . . |
$$ +-------------------+[/go]

White's group has only three liberties (shadowed).

After your move

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Igo Hatsuyōron #120 (really solved by KataGo)

Tips:

in a dead shape (or a seki if you haven't filled outside liberties yet, such as D1, F1), you need to be connected.

in particular, everything needs to be connected to one central stone. Normally 2-1 at A2 is vital for eyespace. But in this case, playing 2-1 doesn't help because A2 and the C3 on the board are too far apart to be connected. But that doesn't mean you can't kill, especially as F1 is an approach liberty that you don't need if W puts themselves in self-atari.

A2 is open enough that it could be an eye. That is, you have enough liberties and W lacks enough liberties to compete for it.

When the problem is so small you can try every variation, it's a good reading exercise anyway.