Diff: Beginner Exercise 156 / Solution

BeginnerExercise156/Solution:page info & history, related pages, related changes

Archived page:	version 12	modified on September 13, 2024 - 03:18	by hnishy
Archived page:	version 10	modified on October 23, 2022 - 06:33	by xela

Edit summary: "new solution"

Switch to diff-in-page view.

Diff: Beginner Exercise 156 / Solution

RecentChanges · StartingPoints · About

Edit page ·Search · Related · Page info · Latest diff

@@ -1,30 +1,25 @@
- $$B Black to win the race
+ $$B Solution
$$-----------------------
$$ . . . . . . . b O 1 . \|
- $$ . . . . . . . X O a X \|
- $$ . . . . . X . X O O X \|
+ $$ . . . . . . . B O a X \|
+ $$ . . . . . X . B O O X \|
$$ . . . . . . . O X X X \|
$$ . . . . . . . O O O c \|
- $$ . . . . . . . . . . d \|
+ $$ . . . . . . . . . . . \|
$$ . . . . . . . . . O . \|
- $$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|
$$ . . . . . . . . . . . \|

- Black wins with B1, ''a'', or ''b''. If Black ''a'' or ''b'', White has a ko threat at ''c''. With B1, White has a ko threat at ''b'' but ''c'' is not sente for White. Thus, Black may exchange ''c'' for ''d'' anytime (= 1 point sente).
+ Black wins with B1, ''a'', or ''b''. B1 is best, with two advantages over the rest:

- So, I conclude B1 is best.
+ 1) White's play at ''c'' is not [sente], and

- [togo]: And even better: If I see this correctly, White's ko threat at ''b'' only kills, if there is a white stone to run to (Although unanswered it weakens Black's stones considerably.).
+ 2) the marked stones have more liberties in some continuations.

- [xela]: Also, ''a'' and ''b'' are different, in that for ''a'', white's ko threat is a threat to capture the corner, whereas for ''b'', white can only threaten [seki]. See the next two diagrams.
-
- $$B Wrong answer 1: big ko threat
+ $$B Comparison 1
$$-----------------------
- $$ . . . . . . . . O 4 . \|
- $$ . . . . . . . X O 1 X \|
- $$ . . . . . X . X O O X \|
+ $$ . . . . . . . 3 O . . \|
+ $$ . . . . 5 4 a B O 1 X \|
+ $$ . . . . . X 6 B O O X \|
$$ . . . . . . . O X X X \|
$$ . . . . . . . O O O 2 \|
$$ . . . . . . . . . . . \|

@@ -29,28 +24,23 @@
$$ . . . . . . . O O O 2 \|
$$ . . . . . . . . . . . \|
$$ . . . . . . . . . O . \|
- $$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|
$$ . . . . . . . . . . . \|

- If black ignores W2, then W4 will capture the black stones
+ If Black chooses ''a'' in the above diagram, W2 forces B3 - it tactically affect the top side. For example, Black can't catch W4 because of W6! - Black can't play at ''a''.

- $$B Wrong answer 2: smaller ko threat
+ $$B Comparison 2
$$-----------------------
- $$ . . . . . . . 1 O 4 . \|
- $$ . . . . . . . X O a X \|
- $$ . . . . . X . X O O X \|
+ $$ . . . . . . . 1 O b . \|
+ $$ . . . . . 2 . B O . X \|
+ $$ . . . . . X . B O O X \|
$$ . . . . . . . O X X X \|
- $$ . . . . . . . O O O 2 \|
+ $$ . . . . . . . O O O a \|
$$ . . . . . . . . . . . \|
$$ . . . . . . . . . O . \|
$$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|
- $$ . . . . . . . . . . . \|

- If black ignores W2, then W4 is seki.
+ If Black chooses ''b'' in the first diagram, the same tactics occurs with more serious effect because White's corner has two liberties. Later, White ''a'' will be sente - White ''b'' next makes seki.
+
----

* __Back to [Beginner Exercises]__