Diff: Beginner Exercise 154 / Solution

BeginnerExercise154/Solution:page info & history, related pages, related changes

Current page:	version 28	modified on September 13, 2024 - 01:33	by hnishy
Archived page:	version 20	modified on May 7, 2009 - 12:45	by Unkx80

Edit summary: "cleanup. delete off-topic, too lengthy and incomplete discussion"

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Diff: Beginner Exercise 154 / Solution

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@@ -1,5 +1,4 @@	edit block
==== Solution ====
-
$$W Life
$$ \| . . . . . . .
$$ \| X X . . . . .

@@ -10,11 +9,9 @@	edit block
$$ \| . . . O O X .
$$ --------------

- W1 makes life.
+ W1 is forced to prevent [snapback] and at the same time lives.

- %%%%
-
- $$Seki
+ $$ Seki
$$ \| . . . . . . .
$$ \| X X . . . . .
$$ \| O X X . . . .

@@ -30,7 +27,7 @@	edit block

==== Failure ====

- $$W Dead
+ $$B Ko
$$ \| . . . . . . .
$$ \| X X . . . . .
$$ \| O X X . . . .

@@ -35,60 +32,15 @@	edit block
$$ \| X X . . . . .
$$ \| O X X . . . .
$$ \| O O X X X . .
- $$ \| . 2 O . X . .
+ $$ \| . O O 3 X . .
$$ \| X O . O X X .
- $$ \| . 1 . O O X .
+ $$ \| a 1 2 O O X .
$$ --------------

- White dies from [snapback] after B2.
+ W2 allows B3 to start a [ko], which White takes first at ''a''. However, this result is inferior to [unconditional life] (including seki) as per [tsumego conventions].

- %%%%
-
- $$W Ko
- $$ \| . . . . . . .
- $$ \| X X . . . . .
- $$ \| O X X . . . .
- $$ \| O O X X X . .
- $$ \| . 1 O 4 X . .
- $$ \| X O . O X X .
- $$ \| a 2 3 O O X .
- $$ --------------
-
- W3 allows B4 to start a [ko], which Black takes first at ''a''. However, this result is inferior to [unconditional life].
+ (In practice, White may choose this line only when value of the move is very small and ko threat situation is exceptionally good.)

- ----
-
- $$W Ko
- $$ \| . . . . . . .
- $$ \| X X . . . . .
- $$ \| O X X . . . .
- $$ \| O O X X X . .
- $$ \| . 1 O 4 X . .
- $$ \| X O . O X X .
- $$ \| . 2 3 O O X .
- $$ --------------
-
- Anonymous spoofer - While this is a Ko, it is in White's favour; is it really a worse outcome than seki? (Note: this comment was originally signed as if it had come from me - [Alex] - but I did not make it)
-
- [fractic]: This ko is not in White's favour at all. Sure he gets to take the ko first but Black loves playing this ko. Black risks absolutly nothing while White's whole group is at risk. See [hanami ko]
-
- [LukeNine45]: White should only go for the ko if White is guaranteed to win it, a case that will be rare since Black risks so little here. In some cases the ko will be better, but usually the seki is. Also I think seki is usually considered better than ko (for the defender) in L&D problems.
-
- [xela]: "White should only go for the ko if White is guaranteed to win it" ... I'm not sure if that's actually true. (I don't mean to be pedantic; I'm testing my own understanding here.) Let's try and work it out:
-
- White takes the ko first. If white wins the ko, the corner is worth six points. If white loses the ko, black has 22 points. If white plays for seki instead of ko, then noone gets any points in the corner (assuming Japanese rules). So let's pretend that black has exactly one ko threat on the board, worth 30 points, and white has exactly one ko threat on the board, worth 23 points, and there are no other ko threats. Now if white plays the ko and wins it (black answers white's ko threat), white is six points ahead compared to playing the seki: this is a mistake by black. Black should ignore white's ko threat and take the corner--i.e, white loses the ko--but white is still one point ahead compared to playing the seki. This is best play for both sides: white should go for the ko and lose it.
-
- Someone please correct me if I've got this wrong. Of course it's all hypothetical--usually there are more ko threats and it's much more complicated. As [LukeNine45] says, in life and death problems (where you're not shown the rest of the board, and know nothing about ko threats) the convention is to prefer the seki solution.
-
- [Bill]: After W1 the position is worth -3.5 points of territory by Japanese scoring. (0.5 point better for White than by [area scoring].) If White wins the ko he gets only 5 points of territory. So his extra move to win the ko gains only 1.5 points (3 points by area scoring).
-
- Since the corner will normally be played out when the hottest play gains 3.5 points (5 points by area scoring), White will usually not be able to effectively make the ko, as winning the ko will not be worth it.
-
- (More later about xela's specific example).
-
- ----
-
- [SnotNose], [unkx80]
----

* __Back to [Beginner Exercises]__

@@ -93,3 +45,4 @@	edit block

* __Back to [Beginner Exercises]__
* __Go to [Beginner Exercise 155]__
+