XuanxuanQijingProblem307/Solution

Solution: W makes a favorable ko  

is the only first move. W takes the ko first here and has a local threat at the marked location. being the only move for B.

Reasoning

would be wrong  

Would result in a miai.

Wrong defense by B. ( at )  

If W is allowed to get , B can't get two eyes.

Wrong attack by W #1  

Black can live unconditionally like this (or capture and the solution sequence follows only lost the local threat).

Slightly more complex but wrong attack by W

Wrong attack by W #2 ( at )  

This is the best for both if is played, B takes the ko first here as opposed to the correct solution where W does.

would be wrong.  

Alive thanks to the miai.

would be wrong.  

W would take the ko first here (notice this is a direct ko).

would be wrong.  

Wrong due to the same miai.

would be wrong.  

Would revert to the previous direct ko where W takes first.

would be wrong. ( at )  

Back to the ko which B takes first.

would be wrong.  

Dead.

Bonus Comment - Altered Situations

Altered Situation #1  

How do you think the change affect the best sequence?

Altered Situation #2  

And here?

Altered Situation #3  

What can W gain here?