Ive done a study for the standard attack on 2-2 on the carpenters square and came to two conclusions i wanted to verify.
The first one is about the preference of which is the standard line with no outside liberties, like it is discussed at senseis. Here the two ways and according to senseis with the second one as standard way for no liberties. http://senseis.xmp.net/?CarpentersSquare
At first glance it seems the circled white stone is needed more in the second variant than in the first. I changed the problem with putting in a connection stone for black and came for both ways to the conclusion that black can now escape.
and black connects with 10 at three (7 and 8 are not really needed for that conclusion)
and here black can also connect. The direction is also chosen by black's 2. As i see no difference it's maybe better to remember only the first version which also works with one liberty. Or did I overlook something ?
Edith says: Removes a wrong arbitrary ston in the diagrams.
Carpenters square
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Shinkenjoe
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cyclops
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Re: Carpenters square
Did you try 
at 6 in your third diagram? To me it seems ko.
edit: it seems Shinkenjoe refuted my suggestion.
at 6 in your third diagram? To me it seems ko.edit: it seems Shinkenjoe refuted my suggestion.
Last edited by cyclops on Thu Jan 10, 2013 2:42 pm, edited 2 times in total.
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Shinkenjoe
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Re: Carpenters square
And now black threatens making a eye at S3, so white has to answer somewhere there. Two possiblities. The first seki
The second alive
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Shinkenjoe
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Re: Carpenters square
The other point that interested me was the how to react on the no brain white answer to the standard defense at 
:
My conclusion is that black can force white on various ways into a two stage approach move ko (right?) in which white has to ignore three black ko threats that looks like this:
I put my thoughts into an sgf which may be a bit confusing as i didn't name all wrong answers as wrong and discussed also many silly moves. It is too broken for the eido sgf player and i cant find the error, so ill just upload it as it works with my two work station sgf players. If i tidy it up and find the error, ill update it.
:
My conclusion is that black can force white on various ways into a two stage approach move ko (right?) in which white has to ignore three black ko threats that looks like this:
I put my thoughts into an sgf which may be a bit confusing as i didn't name all wrong answers as wrong and discussed also many silly moves. It is too broken for the eido sgf player and i cant find the error, so ill just upload it as it works with my two work station sgf players. If i tidy it up and find the error, ill update it.- Attachments
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- 2.sgf
- (7.35 KiB) Downloaded 486 times
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cyclops
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Re: Carpenters square
[edit] sorry, nonsense again by me. B plays 
at b in the next diagram and lives. So must be at a. Now I am convinced by your 3d diagram[/edit]
Again I try to refute your 3d diagram of your first post.
What about this? Next W has a & b as miai to force the ko ( I think ).
at b in the next diagram and lives. So must be at a. Now I am convinced by your 3d diagram[/edit]Again I try to refute your 3d diagram of your first post.
What about this? Next W has a & b as miai to force the ko ( I think ).
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Shinkenjoe
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Re: Carpenters square
to your edit: at a in your diagram would be a mistake as white at 8 with 9 connects. Black would have to fight a ko for connection to the outside
but i gotta admit i'm getting confused right now. Maybe i got a wrong sequence in the questioned third diagram, as i didnt look much at
as it seemed to be easy to cut at b. If I look at it now a and b are miai. for connection.
edit: Maybe you can get me this way, but the following answer still works. A bit easier is this one:
If
at 
or black gets a seki at 
at a in your diagram would be a mistake as white at 8 with 9 connects. Black would have to fight a ko for connection to the outsidebut i gotta admit i'm getting confused right now. Maybe i got a wrong sequence in the questioned third diagram, as i didnt look much at
as it seemed to be easy to cut at b. If I look at it now a and b are miai. for connection.edit: Maybe you can get me this way, but the following answer still works. A bit easier is this one:
If
at or black gets a seki at -
macelee
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Re: Carpenters square
Shinkenjoe, for your original question: why there are two ways to form ko (I will call them variation 1 and 2 here and reproduce the diagrams)?
I summarize what I have read:
* Assume white starts ko in the corner and then give up the ko in exchange for some benefit elsewhere, white would lose fewer points in the corner in variation 2. In variation 1 black would have won the ko by taking and stones, leaving further yose moves to play.
* From black's point of view, when white attacks at
black has two 1-2 moves due to symmetry. Normally black should play the side where by winning the ko in variation 1 he could benefit more in yose.
* As you've correctly pointed out, variation 1 also work when black has external liberties. That is not the case in variation 2 (with one extra liberty, black can continue at the 3-3 point to live)
* One also need to take into account the fact that: in variation 2, assume white wins the ko, black is locally dead as a bulky-five, which has a lot of liberties. Assume white's surrounding stones are not strong enough, there are chances for black to start a capturing race. So white needs to be careful when choosing variation 2.
As you can see all these points are for practical situations. In real games we rarely get shapes as clean as in a textbook. Pro players are strong because they can take these facts into account and made right decisions.
Hope this is useful. For more details I welcome you to follow my articles at http://www.go4go.net/go/carpenter_square and even better comment on my articles there (there is a similar authoring system there supporting diagrams). If a lot of people read those I would have the incentive to translate more topics in the future.
I summarize what I have read:
* Assume white starts ko in the corner and then give up the ko in exchange for some benefit elsewhere, white would lose fewer points in the corner in variation 2. In variation 1 black would have won the ko by taking
and stones, leaving further yose moves to play.* From black's point of view, when white attacks at
black has two 1-2 moves due to symmetry. Normally black should play the side where by winning the ko in variation 1 he could benefit more in yose.* As you've correctly pointed out, variation 1 also work when black has external liberties. That is not the case in variation 2 (with one extra liberty, black can continue at the 3-3 point to live)
* One also need to take into account the fact that: in variation 2, assume white wins the ko, black is locally dead as a bulky-five, which has a lot of liberties. Assume white's surrounding stones are not strong enough, there are chances for black to start a capturing race. So white needs to be careful when choosing variation 2.
As you can see all these points are for practical situations. In real games we rarely get shapes as clean as in a textbook. Pro players are strong because they can take these facts into account and made right decisions.
Hope this is useful. For more details I welcome you to follow my articles at http://www.go4go.net/go/carpenter_square and even better comment on my articles there (there is a similar authoring system there supporting diagrams). If a lot of people read those I would have the incentive to translate more topics in the future.
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Shinkenjoe
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Re: Carpenters square
Thanks very much, macelee.
The differences are more subtle than i thought, but still can be game changing (like the threatening semeai for the outer stones in variant two). I'll have a look at you're articles there, but it can take time with the questions as my time is sparse atm.
The differences are more subtle than i thought, but still can be game changing (like the threatening semeai for the outer stones in variant two). I'll have a look at you're articles there, but it can take time with the questions as my time is sparse atm.