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Offline xela
 Post subject: Re: Tsumegos from real games
Post #21 Posted: Tue Feb 25, 2020 4:12 am 
Lives in gote

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Tsumego 4, minor detail of move order:
Click Here To Show Diagram Code
[go]$$Bc
$$ ---------------------------------------
$$ | . . . . b 9 . . . . . . . . . . . . . |
$$ | . . W . 5 4 0 8 . . . . . . . . . . . |
$$ | . X W a 3 O 1 X O . . . . O X . . . . |
$$ | . X X O 6 X O O 2 O . . . O X X X . . |
$$ | . X O O . 7 X X O . . . . . . . O . . |
$$ | . . X X O O . . O O . . . . X X O . . |
$$ | . . . . X O X X . X O . . . . O . . . |
$$ | . . . X X X O X . X . . . . . . . . . |
$$ | . . X . . O O . . . . . . . . . . . . |[/go]

:b11: at a. If black omits :b9:, then white can play b and save the :wc: stones.

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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #22 Posted: Tue Feb 25, 2020 6:15 am 
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Re: tsumego 3. Here is Katago's analysis.


Suppose first that White pushes, Black blocks and White cuts.
Click Here To Show Diagram Code
[go]$$Wc The four black stones are captured
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X X . . . . . . . . . . . . . |
$$ | . . O X . O . X . . . . . X . X X . . |
$$ | . . O X . . . . . , . . . . . O . . . |
$$ | . . O X . . 7 5 6 . . . . . . . O . . |
$$ | . . O O X X 2 3 4 . . . . . . O X . . |
$$ | . . . O O X 1 X X O . . . . . . O . . |
$$ | . . . . X W W W W X . . . . . . . . . |
$$ | . . . . X . . . . . . . . . . . . . . |
$$ | . . . , . X . . . , . . . . . , . . . |[/go]


(White shouldn't play :w7: at E15, otherwise Black sacrifices three stones and plays :b8: at :w7:.)

If Black protects the four stones with :b6:, then other stones are caught in a ladder.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X X . . . . . . . . . . . . . |
$$ | . . O X . O . X . . . . . X . X X . . |
$$ | . . O X . 6 . . . , . . . . . O . . . |
$$ | . . O X . . . 5 . . . . . . . . O . . |
$$ | . . O O X X 2 3 4 7 . . . . . O X . . |
$$ | . . . O O X 1 X X O . . . . . . O . . |
$$ | . . . . X W W W W X . . . . . . . . . |
$$ | . . . . X . . . . . . . . . . . . . . |
$$ | . . . , . X . . . , . . . . . , . . . |[/go]


However, before blocking, Black may want to make the exchange K14-L13 first, in which case the above variations don't work anymore, so White has to play :w5: differently. Black has to extend at :b6: otherwise the preceding variations work again, and then :w7: captures the cutting stone K12 in a ladder.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X X . . . . . . . . . . . . . |
$$ | . . O X . O . X . . . . . X . X X . . |
$$ | . . O X . . . . . , . . . . . O . . . |
$$ | . . O X . . . . . 6 . . . . . . O . . |
$$ | . . O O X X 4 . . 2 5 . . . . O X . . |
$$ | . . . O O X 1 X X O 3 . . . . . O . . |
$$ | . . . . X W W W W X . . . . . . . . . |
$$ | . . . . X . . . . 7 . . . . . . . . . |
$$ | . . . , . X . . . , . . . . . , . . . |[/go]


xela wrote:
But I don't think of this as tesuji, white is playing fairly blunt moves.


I know these moves are blunt, but because my reading is too shallow, I couldn't see that a succession of 7 blunt moves actually works. That's one of the reasons why I am a kyu player...
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #23 Posted: Tue Feb 25, 2020 6:30 am 
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Tsumego 4, analysis by Katago:

Suppose White cuts with :w6: as in Kirby's and xela's posts, then White loses somes stones but ends in sente: after :w10:, Black needs to play "a".
Click Here To Show Diagram Code
[go]$$Bc
$$ ---------------------------------------
$$ | . . . . 9 8 . . . . . . . . . . . . . |
$$ | . . O . 5 4 . 0 . . . . . . . . . . . |
$$ | . X O a 3 O 1 X O . . . . O X . . . . |
$$ | . X X O 6 X O O 2 O . . . O X X X . . |
$$ | . X O O . 7 X X O . . . . . . . O . . |
$$ | . . X X O O . . O O . . . . X X O . . |
$$ | . . . . X O X X . X O . . . . O . . . |
$$ | . . . X X X O X . X . . . . . . . . . |
$$ | . . X . . O O . . . . . . . . . . . . |[/go]


So White won't bother cutting at :w6: and plays as follows:
Click Here To Show Diagram Code
[go]$$Bc
$$ ---------------------------------------
$$ | . . . . 7 6 . . . . . . . . . . . . . |
$$ | . . O . 5 4 . 8 . . . . . . . . . . . |
$$ | . X O . 3 O 1 X O . . . . O X . . . . |
$$ | . X X O . X O O 2 O . . . O X X X . . |
$$ | . X O O 9 . X X O . . . . . . . O . . |
$$ | . . X X O O . . O O . . . . X X O . . |
$$ | . . . . X O X X . X O . . . . O . . . |
$$ | . . . X X X O X . X . . . . . . . . . |
$$ | . . X . . O O . . . . . . . . . . . . |[/go]
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #24 Posted: Wed Apr 29, 2020 8:48 am 
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Tsumego #5: An easy one but I didn't take the trouble to read it during the game.

White to play. Assume White is alive. What is the status of the black group?

Click Here To Show Diagram Code
[go]$$Wc
$$ ----------------
$$ O O X . . . . . |
$$ O X X X X . . . |
$$ O O O O O X X X |
$$ . O O . O O O O |[/go]

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Offline EricBackus
 Post subject: Re: Tsumegos from real games
Post #25 Posted: Wed Apr 29, 2020 10:03 am 
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jlt wrote:
Tsumego #5: An easy one but I didn't take the trouble to read it during the game.

White to play. Assume White is alive. What is the status of the black group?

Click Here To Show Diagram Code
[go]$$Wc
$$ ----------------
$$ O O X . . . . . |
$$ O X X X X . . . |
$$ O O O O O X X X |
$$ . O O . O O O O |[/go]

I think: Black is alive, but white can make a gote seki.

Click Here To Show Diagram Code
[go]$$Wc This attack fails
$$ ----------------
$$ O O X . . 1 2 5 |
$$ O X X X X 4 3 6 |
$$ O O O O O X X X |
$$ . O O . O O O O |[/go]

Click Here To Show Diagram Code
[go]$$Wc Gote seki
$$ ----------------
$$ O O X . 5 2 1 . |
$$ O X X X X 4 . 3 |
$$ O O O O O X X X |
$$ . O O . O O O O |[/go]

Black could alternatively make this a ko, but this is unlikely to be better than seki.
Click Here To Show Diagram Code
[go]$$Wc Ko, white takes first
$$ ----------------
$$ O O X . 3 4 1 . |
$$ O X X X X . 2 . |
$$ O O O O O X X X |
$$ . O O . O O O O |[/go]

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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #26 Posted: Sat May 09, 2020 3:57 am 
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Tsumego #6: Black to play. Can Black kill a group?

Click Here To Show Diagram Code
[go]$$Bc Black to play
$$ ---------------------------------------
$$ | . . . . . . . O . . . . . . . . . . . |
$$ | . O X . . O O . O X . X X O X O O . . |
$$ | . O X O O O X O O X . . O X . X O . . |
$$ | O X O O X X X X X , . . . X X X . O . |
$$ | . X X X . . . . . . X . O . . . X O O |
$$ | . X . . X . O O O . X O . . . . X O X |
$$ | . . X O . O . X O X O . . O O X . X . |
$$ | . X O . . . O X O X . O O . O O X . X |
$$ | . X O . O . O O X X . X O O X X X X O |
$$ | X O O X O X . . . , . X O X . X . O . |
$$ | . X . O O X . O . . . . X . X X . O . |
$$ | . . . O X X . . . . X X X X O O O . . |
$$ | . X O O . . . X . X X O O O O X . . . |
$$ | . X O X . . . . O X O . . . O X O O . |
$$ | . X O X . X . X X O . . O X . X X X . |
$$ | . X X O . . X . O , O . O X . , . . . |
$$ | . . X O . O X . X O . O X O . X . . . |
$$ | . O O . O . O X X X O O X X . . . . . |
$$ | . . . . . . O . O O . . . . . . . . . |
$$ ---------------------------------------[/go]

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Offline Harleqin
 Post subject: Re: Tsumegos from real games
Post #27 Posted: Sat May 09, 2020 6:04 am 
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Like this probably:

Click Here To Show Diagram Code
[go]$$Bc Black to play
$$ ---------------------------------------
$$ | . . . . . . . O . . . . . . . . . . . |
$$ | . O X . . O O . O X . X X O X O O . . |
$$ | . O X O O O X O O X . . O X . X O . . |
$$ | O X O O X X X X X , . . . X X X . O . |
$$ | . X X X . . . . . . X . O . . . X O O |
$$ | . X . . X . O O O . X O 3 a . . X O X |
$$ | . . X O . O . X O X O 1 . O O X . X . |
$$ | . X O . . . O X O X 2 O O . O O X . X |
$$ | . X O . O . O O X X . X O O X X X X O |
$$ | X O O X O X . . . , . X O X . X . O . |
$$ | . X . O O X . O . . . . X . X X . O . |
$$ | . . . O X X . . . . X X X X O O O . . |
$$ | . X O O . . . X . X X O O O O X . . . |
$$ | . X O X . . . . O X O . . . O X O O . |
$$ | . X O X . X . X X O . . O X . X X X . |
$$ | . X X O . . X . O , O . O X . , . . . |
$$ | . . X O . O X . X O . O X O . X . . . |
$$ | . O O . O . O X X X O O X X . . . . . |
$$ | . . . . . . O . O O . . . . . . . . . |
$$ ---------------------------------------[/go]


If 2 captures, 3 at a.

_________________
A good system naturally covers all corner cases without further effort.

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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #28 Posted: Sat May 09, 2020 8:33 am 
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It seems that this is the correct :b1:, but White can play :w2: differently and get a ko.
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Offline Harleqin
 Post subject: Re: Tsumegos from real games
Post #29 Posted: Sun May 10, 2020 2:54 pm 
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Oh.
Click Here To Show Diagram Code
[go]$$Bc Black to play
$$ ---------------------------------------
$$ | . . . . . . . O . . . . . . . . . . . |
$$ | . O X . . O O . O X . X X O X O O . . |
$$ | . O X O O O X O O X . . O X . X O . . |
$$ | O X O O X X X X X , . . . X X X . O . |
$$ | . X X X . . . . . . X 7 O 2 . . X O O |
$$ | . X . . X . O O O . X O . 4 3 . X O X |
$$ | . . X O . O . X O X O 1 6 O O X . X . |
$$ | . X O . . . O X O X 5 O O . O O X . X |
$$ | . X O . O . O O X X . X O O X X X X O |
$$ | X O O X O X . . . , . X O X . X . O . |
$$ | . X . O O X . O . . . . X . X X . O . |
$$ | . . . O X X . . . . X X X X O O O . . |
$$ | . X O O . . . X . X X O O O O X . . . |
$$ | . X O X . . . . O X O . . . O X O O . |
$$ | . X O X . X . X X O . . O X . X X X . |
$$ | . X X O . . X . O , O . O X . , . . . |
$$ | . . X O . O X . X O . O X O . X . . . |
$$ | . O O . O . O X X X O O X X . . . . . |
$$ | . . . . . . O . O O . . . . . . . . . |
$$ ---------------------------------------[/go]

_________________
A good system naturally covers all corner cases without further effort.

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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #30 Posted: Fri May 22, 2020 8:29 am 
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This one should be easy.

Problem #7: White to play and win the capturing race.

Click Here To Show Diagram Code
[go]$$Wc White to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . X . X X . X . . |
$$ | . . . X . . . . X O O O X X X X O O . |
$$ | . . O . . X . . X X . O X O O X O . . |
$$ | . . . O . . . . . , X O X O X X O . . |
$$ | . . . . . . . . . . X O O O O X X O . |
$$ | . . O . . . . . . . . O X X . O X O . |
$$ | . . . . . . . . . . X O . O O O X O . |
$$ | . . . . . . . . . . X O O O X X X O . |
$$ | . . . . . . . . . . X O X X X X O O . |
$$ | . . . X . . . . O O X O X O . X O O X |
$$ | . . . X O . . . O X . X O . O X O X . |
$$ | . . X O . O O O X X . . . . . X X X . |
$$ | . . X O . X X O X O . O O O O O O O . |
$$ | . . X O . . . X X O . . X X X X O . . |
$$ | . X O O O X . X . O X . . X . X O . . |
$$ | . X O , O X . . . O . . O X X O . . . |
$$ | . . X O O O X X X O . X O X O O . . . |
$$ | . X . X . O X . X O X . X . X O . . . |
$$ | . . X . . . . . X O . . . X O O . . . |
$$ ---------------------------------------[/go]
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Offline Knotwilg
 Post subject: Re: Tsumegos from real games
Post #31 Posted: Fri May 22, 2020 11:28 am 
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Click Here To Show Diagram Code
[go]$$W White to play
$$ ---------------------------------------
$$ | . . . . . . . . 4 2 3 X . X X . X . . |
$$ | . . . X . . . . X O O O X X X X O O . |
$$ | . . O . . X . . X X B O X O O X O . . |
$$ | . . . O . . . . . , X O X O X X O . . |
$$ | . . . . . . . . . . X O O O O X X O . |
$$ | . . O . . . . . . . B O X X 6 O X O . |
$$ | . . . . . . . . . . X O 7 O O O X O . |
$$ | . . . . . . . . . . X O O O X X X O . |
$$ | . . . . . . . . . . X O X X X X O O . |
$$ | . . . X . . . . O O X O X O W X O O X |
$$ | . . . X O . . . O X . X O . O X O X . |
$$ | . . X O . O O O X X . . . . W X X X 1 |
$$ | . . X O . X X O X O . O O O O O O O 5 |
$$ | . . X O . . . X X O . . X X X X O . . |
$$ | . X O O O X . X . O X . . X . X O . . |
$$ | . X O , O X . . . O . . O X X O . . . |
$$ | . . X O O O X X X O . X O X O O . . . |
$$ | . X . X . O X . X O X . X . X O . . . |
$$ | . . X . . . . . X O . . . X O O . . . |
$$ ---------------------------------------[/go]


The marked stones are outside liberties, incidental to the problem/

Click Here To Show Diagram Code
[go]$$B continuation
$$ ---------------------------------------
$$ | . . . . . . . . X X O X 4 X X . X . . |
$$ | . . . X . . . . X O O O X X X X O O . |
$$ | . . O . . X . . X X B O X O O X O . . |
$$ | . . . O . . . . . , X O X O X X O . . |
$$ | . . . . . . . . . . X O O O O X X O . |
$$ | . . O . . . . . . . B O . 1 3 O X O . |
$$ | . . . . . . . . . . X O O O O O X O . |
$$ | . . . . . . . . . . X O O O X X X O . |
$$ | . . . . . . . . . . X O X X X X O O . |
$$ | . . . X . . . . O O X O X O W X O O X |
$$ | . . . X O . . . O X . X O . O X O X 2 |
$$ | . . X O . O O O X X . . . . W X X X O |
$$ | . . X O . X X O X O . O O O O O O O O |
$$ | . . X O . . . X X O . . X X X X O . . |
$$ | . X O O O X . X . O X . . X . X O . . |
$$ | . X O , O X . . . O . . O X X O . . . |
$$ | . . X O O O X X X O . X O X O O . . . |
$$ | . X . X . O X . X O X . X . X O . . . |
$$ | . . X . . . . . X O . . . X O O . . . |
$$ ---------------------------------------[/go]


White takes first

Click Here To Show Diagram Code
[go]$$W White to play
$$ ---------------------------------------
$$ | . . . . . . . . 4 1 8 X 6 X X 9 X 7 . |
$$ | . . . X . . . . X O O O X X X X O O . |
$$ | . . O . . X . . X X B O X O O X O . . |
$$ | . . . O . . . . . , X O X O X X O . . |
$$ | . . . . . . . . . . X O O O O X X O . |
$$ | . . O . . . . . . . B O X X . O X O . |
$$ | . . . . . . . . . . X O . O O O X O . |
$$ | . . . . . . . . . . X O O O X X X O . |
$$ | . . . . . . . . . . X O X X X X O O 5 |
$$ | . . . X . . . . O O X O X O W X O O X |
$$ | . . . X O . . . O X . X O . O X O X . |
$$ | . . X O . O O O X X . . . . W X X X 2 |
$$ | . . X O . X X O X O . O O O O O O O 3 |
$$ | . . X O . . . X X O . . X X X X O . . |
$$ | . X O O O X . X . O X . . X . X O . . |
$$ | . X O , O X . . . O . . O X X O . . . |
$$ | . . X O O O X X X O . X O X O O . . . |
$$ | . X . X . O X . X O X . X . X O . . . |
$$ | . . X . . . . . X O . . . X O O . . . |
$$ ---------------------------------------[/go]


White will always take a ko to prevent Black from connecting.


Edited diagram 2, voiding jlt's next comment


Last edited by Knotwilg on Fri May 22, 2020 1:29 pm, edited 3 times in total.
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #32 Posted: Fri May 22, 2020 1:26 pm 
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Knotwilg, you mistyped what you had in mind in diagram 2 since there are two :w2: on the board and :b7: on an intersection that is already occupied by a white stone.

Anyway I think that :w1: starting from your diagram 1 leads to a ko (this is what happened in my game), while :w1: in your diagram 3 is the correct move, White wins the semeai without needing to fight a ko.

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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #33 Posted: Tue May 26, 2020 11:42 am 
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Problem #8: Black to play. Can Black save the marked stone?

Click Here To Show Diagram Code
[go]$$Bc Black to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . O . . . . . . . O O X . . . |
$$ | . O . B O . . . . , . . O X O X . . . |
$$ | O . O O X O . . . . . O . X O X . . . |
$$ | . O X X X . . . . . . . X . X X O . . |
$$ | . X X . X . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , O . . . . , . . . . . , . . . |
$$ | . . O O X . . . . . . . . . . . . . . |
$$ | . . X X . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . . O X . |
$$ | . . . . . . . . . . . . . . . . O X . |
$$ | . . X . . . . . . . . . . . . . O X . |
$$ | . . . , O . . . . X . . X . . O X . . |
$$ | . . . O . . . O . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #34 Posted: Wed Jun 17, 2020 12:38 am 
Gosei
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Possible variation:

Click Here To Show Diagram Code
[go]$$Bc Black to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . 7 3 . . . . . . . . . . . . . . . . |
$$ | . 4 . . 5 O . . . . . . . O O X . . . |
$$ | . O 1 B O 6 . . . , . . O X O X . . . |
$$ | O 2 O O X O . . . . . O . X O X . . . |
$$ | . O X X X . . . . . . . X . X X O . . |
$$ | . X X . X . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #35 Posted: Wed Jun 17, 2020 12:48 am 
Gosei
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Problem #9. I was Black in this game. Between moves 50 and 130 I thought that I had killed the upper left corner. Probably White thought the same as well, as he didn't try to live. When he finally made an attempt at move 130, he didn't make the correct choice.

White to play and save the marked stones.

Click Here To Show Diagram Code
[go]$$Wc White to play and save the marked stones
$$ ---------------------------------------
$$ | . . . . . . . . X . . . . . . . X O . |
$$ | . . . . . . X X . X O . . . O X . O . |
$$ | . . . . X . O X X O O . O O O X X X . |
$$ | . . W W X . . O O , . . . X X X O X . |
$$ | . . . . . . O . X O . . X . X O O O . |
$$ | . . X X . X X O . . . . X X X X O . . |
$$ | . . . . . . . O . . . . X O O O . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . X X O . . . X . O O X . . |
$$ | . . X X X . . O . , . O . X O X X . . |
$$ | . . X O . O . . . . . . O O X O . . . |
$$ | . . X O . O . . . . . . . O X O O X . |
$$ | . . O X . . . . . . . . X O X . X . . |
$$ | . . O . . . . . . . . O O X . X . . . |
$$ | . . . . . . . O X . O O X . . . . . . |
$$ | . . . O . . . . O O . X . X . O X . . |
$$ | . . . . O . O O X X O O X . . X . . . |
$$ | . . . O X X X X O X X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
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Offline Knotwilg
 Post subject: Re: Tsumegos from real games
Post #36 Posted: Wed Jun 17, 2020 2:38 am 
Gosei
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Click Here To Show Diagram Code
[go]$$Wc White to play and save the marked stones
$$ ---------------------------------------
$$ | . . . . . . . . X . . . . . . . X O . |
$$ | . 1 . a . . X X . X O . . . O X . O . |
$$ | . . . . X . O X X O O . O O O X X X . |
$$ | . . W W X . . O O , . . . X X X O X . |
$$ | . b . . . . O . X O . . X . X O O O . |
$$ | . . X X . X X O . . . . X X X X O . . |
$$ | . . . . . . . O . . . . X O O O . . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . . . . . X X O . . . X . O O X . . |
$$ | . . X X X . . O . , . O . X O X X . . |
$$ | . . X O . O . . . . . . O O X O . . . |
$$ | . . X O . O . . . . . . . O X O O X . |
$$ | . . O X . . . . . . . . X O X . X . . |
$$ | . . O . . . . . . . . O O X . X . . . |
$$ | . . . . . . . O X . O O X . . . . . . |
$$ | . . . O . . . . O O . X . X . O X . . |
$$ | . . . . O . O O X X O O X . . X . . . |
$$ | . . . O X X X X O X X . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Does :w1: make miai of A and B?
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #37 Posted: Wed Jun 17, 2020 2:58 am 
Gosei
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Not sure.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . X . . . . . . . X O . |
$$ | . 1 . 3 4 . X X . X O . . . O X . O . |
$$ | . . . . X . O X X O O . O O O X X X . |
$$ | . . W W X . . O O , . . . X X X O X . |
$$ | . 2 . . . . O . X O . . X . X O O O . |
$$ | . . X X . X X O . . . . X X X X O . . |
$$ | . . . . . . . O . . . . X O O O . . . |
$$ | . . . . . . . . . . . . . . . . O . . |[/go]


and then?


This seems to lead to a ko
Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . 8 9 . . . . . X . . . . . . . X O . |
$$ | 0 1 . 3 4 . X X . X O . . . O X . O . |
$$ | . 6 . 5 X . O X X O O . O O O X X X . |
$$ | . 7 W W X . . O O , . . . X X X O X . |
$$ | . 2 . . . . O . X O . . X . X O O O . |
$$ | . . X X . X X O . . . . X X X X O . . |
$$ | . . . . . . . O . . . . X O O O . . . |
$$ | . . . . . . . . . . . . . . . . O . . |[/go]


Katago suggests another move

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | 9 . . . . . . . X . . . . . . . X O . |
$$ | 6 5 . 1 3 4 X X . X O . . . O X . O . |
$$ | . 7 . 8 X . O X X O O . O O O X X X . |
$$ | . . W W X . . O O , . . . X X X O X . |
$$ | . 2 . . . . O . X O . . X . X O O O . |
$$ | . . X X . X X O . . . . X X X X O . . |
$$ | . . . . . . . O . . . . X O O O . . . |
$$ | . . . . . . . . . . . . . . . . O . . |[/go]


It is really necessary for Black to block at :4:, otherwise a variation like this can happen:

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . 8 . X . . . . . . . X O . |
$$ | . . . 1 3 5 X X . X O . . . O X . O . |
$$ | . 4 . . X 6 O X X O O . O O O X X X . |
$$ | . . W W X . 7 O O , . . . X X X O X . |
$$ | . 2 . . 9 . O . X O . . X . X O O O . |
$$ | . . X X . X X O . . . . X X X X O . . |
$$ | . . . . . . . O . . . . X O O O . . . |
$$ | . . . . . . . . . . . . . . . . O . . |[/go]
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #38 Posted: Tue Nov 10, 2020 12:02 pm 
Gosei
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Problem #10, White to play. What is the status of the C10 group?

Click Here To Show Diagram Code
[go]$$Wc White to play
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . O . . O O . . . . . . . . O O O . . |
$$ | . . . . O X . X . . . O O O X O X . . |
$$ | X O O O X X . . . , . O X X X X . X . |
$$ | . X X . . . . . . . X O . . . X . . . |
$$ | . . X . X . . . . . . O O . X O O . . |
$$ | . O . . O X . X . X . O X X . O X . . |
$$ | . . O O O X . . . . X . . . O O . . . |
$$ | X . O X O O . O X X . . X X X O O . . |
$$ | . . O X O . O X X O . . . . . O X . . |
$$ | O O X X X . X O O O . . O O O O . X . |
$$ | . X X . . X . . X O O O X X X . . . . |
$$ | . . . X . X . X . O X X . . . . X . . |
$$ | . . X O O O O . O . . . . . X . . X . |
$$ | . . X O . . O . O . O O . . . . X . O |
$$ | . . X O X O X X . , X O . X O O X O . |
$$ | . . O O X X . . X . X O . X X O O . O |
$$ | . . . . X . . . . . . X X O X . . O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ ---------------------------------------[/go]

This post by jlt was liked by: marvin
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #39 Posted: Thu Nov 12, 2020 1:37 pm 
Gosei
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Answer:

It's a ko.

Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . O . . O O . . . . . . . . O O O . . |
$$ | . . . . O X . X . . . O O O X O X . . |
$$ | X O O O X X . . . , . O X X X X . X . |
$$ | 2 X X . . . . . . . X O . . . X . . . |
$$ | 1 5 X . X . . . . . . O O . X O O . . |
$$ | 8 O 7 . O X . X . X . O X X . O X . . |
$$ | 3 6 O O O X . . . . X . . . O O . . . |
$$ | X 4 O X O O . O X X . . X X X O O . . |
$$ | . . O X O . O X X O . . . . . O X . . |
$$ | O O X X X . X O O O . . O O O O . X . |
$$ | . X X . . X . . X O O O X X X . . . . |
$$ | . . . X . X . X . O X X . . . . X . . |
$$ | . . X O O O O . O . . . . . X . . X . |
$$ | . . X O . . O . O . O O . . . . X . O |
$$ | . . X O X O X X . , X O . X O O X O . |
$$ | . . O O X X . . X . X O . X X O O . O |
$$ | . . . . X . . . . . . X X O X . . O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ ---------------------------------------[/go]


White has local ko threats: capture A16 or capture F13.

In order to live, White just needs to ignore one ko threat and then can live with B10: after :w9: ko threat, :b10: responds, :w11: takes ko, :b12: ko threat, then White is alive (if Black a then White b).

Click Here To Show Diagram Code
[go]$$Wm11
$$ | X X X . . . . . . . X O . . . X . . . |
$$ | O O X . X . . . . . . O O . X O O . . |
$$ | a O O . O X . X . X . O X X . O X . . |
$$ | 1 X O O O X . . . . X . . . O O . . . |
$$ | X X O X O O . O X X . . X X X O O . . |
$$ | b 3 O X O . O X X O . . . . . O X . . |
$$ | O O X X X . X O O O . . O O O O . X . |
$$ | . X X . . X . . X O O O X X X . . . . |
$$ | . . . X . X . X . O X X . . . . X . . |[/go]


Move :w1: is interesting because go problems rarely teach us these kinds of moves. In most go problems, only one group is involved and we don't threaten to connect to another group before living locally.
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Offline jlt
 Post subject: Re: Tsumegos from real games
Post #40 Posted: Thu Nov 12, 2020 2:20 pm 
Gosei
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Problem #11, White to play.

Click Here To Show Diagram Code
[go]$$Wc
$$ ------------
$$ . X . X . . |
$$ . X . . O . |
$$ X . . O . . |
$$ X . , X O . |
$$ X . . X O . |
$$ . . . O X . |
$$ . X . . X . |
$$ . . . . . . |[/go]
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