Diagram 20.1: White to play
help in any way?
Diagram 20.2: False hope
is incorrect. Black is expecting this sequence similar to Diagram 19.2.
would help in this case. However......
Diagram 20.3: Black fails
is the correct answer. Note that white can use this sequence in Shape 19 as well.
Diagram 20.4: Continued (12=*bs*, 13=*bx*)
Black is one liberty too short and cannot play 'a'.
Diagram 20.5: Black fails
So black has to block at *b2*. However,
is incorrect. This result is the same as Diagram 19.3 and black fails to make use of *bs*.
Diagram 20.6: Solution 1
Unlike Diagram 19.4,
tesuji now works. Thanks to
black can throw in
to start a ko fight.
Diagram 20.7: Variation
may atari from the other side, forming a different ko. But note that black takes the ko first so this result cannot be good for white.
Diagram 20.8: Solution 2
in the previous diagram appears to be the key point,
wants to occupy that location first. To avoid the failure in Diagram 20.5,
is a must.
is a nice idea. Black has to go back to
to avoid the Bulky Five killing shape. So the result is a ko. If black wins the ko fight by connecting at *w5*, white can still play 'a' to form a seki, destroying 9 points of territory, although black also has a yose at 'b' that can get a few points back. Overall this solution seems to be slightly worse than Solution 1 for black.
Diagram 20.9: White fails
is a thoughtless move, hoping black to block at 'a' so that knowledge in Shape 7
can apply. But
is good - please verify that black is unconditionally alive now.
To summarise: black corner is quite resilient because of the hane move. Diagram 20.6 and Diagram 20.8 are the right solutions, resulting in ko.