Capturing Race Exercise 24 / Attempts

Attempt #1 - A ko  

unkx80: There is a ko. But I think I have seen this problem before, so I think ko is not the solution.

Attempt #2 ( at the marked stone)  

ProtoDeuteric: I hate to say it, but this was actually my first reading. I saw the in the Attempt #1 diagram because I got really greedy. This still probably wrong, so I might not need to be so ex post facto righteous.

Attempt #2 - Still a ko  

unkx80: is a tesuji. In the end, has to make a throw-in ko. Nice attempts anyway. =)

Oki  

Bill: I think is a good reply.

Extra liberty  

Bill: is a simple reply. Now if , wins, since becomes a liberty.

 

tderz: Having seen above, I also considered here:
(after all you think Black should be able to pull off something)

 

tderz: looks bad, it gives Black good opportunities

i) no ko  

tderz: no ko after

i-1)  

tderz:

 

tderz: ko in favour for Black (captures first)
(i.e. better than unkx80's ko. This is due to White's bad above)

ii)  

tderz: this should revert to variations of ProtoDeuteric above.

ii-1)  

tderz: is it??
at a

ii-2)  

tderz: is a mistake
at a

iii)  

tderz: also considering here...

iii)  

tderz: B has lost

iv)  

tderz: creates 5 liberties for Black, but doesn't take one away from White.

iv-1)  

tderz: , taking outside liberties,
should revert to some above variations.

iv-1)  

tderz: at a
favourable ko for Black

 

tderz: Question: both moves a, b can thus lead to kos (un/favourable), wins or losses, depending on White moves (correct or flawed);
is there still one move better, or does it not matter?

Solution?  

unkx80: I think this might be the intended solution.