Hi,

I have a question concerning this kind of invasion:

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[go]$$c invasion
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . . . . . . . . . .
$$ | . . . X . . . . . ,
$$ | . . W . . . . . . .
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

Normally white now makes a ko. But recently I had this played against me, which josekipedia refers to as "trick play" without further comment:

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . W X . . . . . . .
$$ | . . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

I don't know how to play here as black. Everything I tried ends with white living directly or being able to cut black, which is a problem if black is not strong in the vicinity.

It seems like black's C5 move might better be at B5.

Click Here To Show Diagram Code

[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . B . . . . . . . .
$$ | . . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

But in your continuation, doesn't B6 A4 B2 kill?

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . X X . . . . . . .
$$ | . O X . . . . . . .
$$ | O . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . B . . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

Or if W doesn't make a tiger's mouth, there's still a ko.

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . X X . . . . . . .
$$ | 6 O X . . . . . . .
$$ | . O O X . . . . . ,
$$ | 4 . O X . . . . . .
$$ | 7 2 3 1 . . . . . .
$$ | . 5 . . . . . . . .
$$ ---------------------[/go]

I thought that white first hanes at the other side

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . 1 X . . . . . . .
$$ | . O X . . . . . . .
$$ | . . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . . 4 2 3 . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

Now black has to worry about the cut at E3 if he is not strong around. And if black fixes the cut white lives at B4.

First to answer the original question, just block is correct. That exchange is white's right, but doesn't really help the corner live so it will likely still be the same ko as if white didn't make that exchange, and that exchange is a slight loss for white (it makes black stronger on the outside and increase his influence on the left side).

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[go]$$Wc "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . 2 X . . . . . . .
$$ | . 1 X . . . . . . .
$$ | . . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . . . . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

The continuation splittingfield worries about is indeed more likely for white, but it's locally dead with the bad aji of the cut, the same as without the bad exchange. White can then try a or b. The cut of a doesn't quite capture anything yet, whilst b clamp might escape with a 2nd line crawl that's usually worse than death.

Click Here To Show Diagram Code

[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . 1 X . . . . . . .
$$ | 7 O X . . . . . . .
$$ | . 5 O X . . . . . ,
$$ | . 6 O X a . . . . .
$$ | . . 4 2 3 b . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

Note that in these variations white's hane-block exchange is a bad exchange as they made black stronger and with more eyeshape than without:

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

And now to correct lodestone's comments:


Probably not unless the outside is special. White can live small like this:

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

Or start the ko and black's outside is super weak (at a) if white wins it

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

Or play somewhat heavier and just try living:

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

or if black extends then clamp either gets a in sente to live or escapes on 2nd line:

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[go]$$Wc
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . B . 4 . . . . . .
$$ | . . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . . 3 1 2 5 . . . .
$$ | . . . a . . . . . .
$$ ---------------------[/go]

Maybe, but with very bad aji. The much better way to kill is:

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . X X . . . . . . .
$$ | . O X . . . . . . .
$$ | O 4 O X . . . . . ,
$$ | 6 3 O X . . . . . .
$$ | . 2 1 . 7 . . . . .
$$ | . 5 . . . . . . . .
$$ ---------------------[/go]

No, dead:

Click Here To Show Diagram Code

[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . X X . . . . . . .
$$ | 7 O X . . . . . . .
$$ | 8 O O X . . . . . ,
$$ | 3 . O X . . . . . .
$$ | 9 2 4 1 . . . . . .
$$ | . 6 5 . . . . . . .
$$ ---------------------[/go]

Thanks for your answer, I am more than satisfied!

actually I think often a bigger reason is that after black plays the key point at D2, it becomes a flower ko for b (comparatively).

So often its not so much a trick play as a mistake, but it depends on the outside

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[go]$$c "unconditional death"
$$ | . . . . . . . . . .
$$ | . 3 . . . . . . . .
$$ | . 2 X . . . . . . .
$$ | . O X . . . . . . .
$$ | 4 . O X . . . . . ,
$$ | . 5 O X . . . . . .
$$ | . . . 1 . . . . . .
$$ | . . . . . . . . . .
$$ ---------------------[/go]

Click Here To Show Diagram Code

[go]$$c "depends on outside"
$$ | . . . . . . . . . .
$$ | . 3 0 . . . . . . .
$$ | 5 2 X . . . . . . .
$$ | . O X . . . . . . .
$$ | 6 . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | 9 . 4 1 . . . . . .
$$ | . 8 7 . . . . . . .
$$ ---------------------[/go]

locally this is unconditional death, but the C7 cut is severe - B needs to be able to play A7 and A6 in response to B3 and A3

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[go]$$c "bad ko"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . 3 X . . . . . . .
$$ | 4 O X . . . . . . .
$$ | . . O X . . . . . ,
$$ | 5 . O X . . . . . .
$$ | 6 7 2 1 . . . . . .
$$ | 9 8 . . . . . . . .
$$ ---------------------[/go]

if B loses the ko, it looks like this

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . X X . . . . . . .
$$ | O O X . . . . . . .
$$ | . . O X . . . . . ,
$$ | X O O X . . . . . .
$$ | O . O X . . . . . .
$$ | . O O . . . . . . .
$$ ---------------------[/go]

If B loses the ko in the normal variation in looks like this

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[go]$$c "trick play"
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . . X . . . . . . .
$$ | . . X . . . . . . .
$$ | . . O X . . . . . ,
$$ | . . O X . . . . . .
$$ | . O . O X . . . . .
$$ | . . O . O . . . . .
$$ ---------------------[/go]

B's shape is more broken