I am reading about the knight-move tesuji at 'b' to capture a white group like this, where 'a' fails after repeated ataris by white.

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

The book shows how here fails:

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

and how here fails:

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

But it does not show what happens after this :

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

Is this loose ladder really the best black can do?

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

_________________
Regards,

Peter

Are you sure that's what the book says? As you say white can escape so black fails.

This is the knight's move that works in this situation (sometimes both work, but here the shortage of liberties of the black stone at the top means black has to go this way).

Click Here To Show Diagram Code

[go]$$B
$$ ------------------
$$ | . . . . . . . . .
$$ | . . X X . . . . .
$$ | . X O O X . . . .
$$ | . X . O . . . . .
$$ | . . X . . c . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . .[/go]

If you move one white stone then b works ...

Click Here To Show Diagram Code

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

Yes, sorry, I had the arrangement of white stones slightly wrong, and did not appreciate how much of a difference that would make to black's weak stone and the sequence.

_________________
Regards,

Peter

You should play the knight's net relative to where your weakest side is.

There is a useful heuristic in Go where if a move creates a connection that's too weak, then often if you "pull the move back" a space, usually creating a knight's move, you get a connection that works.

For example, in the following position, ''a'' does not work for black because white can push and cut at ''b'' and capture either the corner or the outside. But if black pulls his stone a step further away from white and plays the knight's move at ''c'' instead, then he produces a safe connection.

Click Here To Show Diagram Code

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

Similarly in this classic tesuji, ''a'' doesn't work for black, but ''b'' does.

Click Here To Show Diagram Code

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

In your example, looking at the two marked black stones, the one on the top side is weaker. So applying the heuristic, your first instinct should be ''a'', pulling the netting move back into a knight's move on the weak side. As opposed to ''b'', which makes the gap on the weak side even larger (two spaces instead of one space) and therefore even easier to for white to break through.

Click Here To Show Diagram Code

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