As far as i can tell, all moves for black inside are equivalent. Is that not the case?
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That is not the case.
hint
1 creates seki, 2 kill.
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response to hint
The two moves that kill are not equivalent: one of them leaves an open ko threat, the other does not.
Therefore, there is one objectively best move.
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I’m confused why not all moves lead to seki. Black plays inside, then white simply does not play inside.
Black wouldn’t actually do this unless Black’s outside comes under threat, but:
Black could play inside again.
(In that case, White can capture, and then Black plays inside yet again.)
Why would black play inside? I don’t see why a threat would cause them to play inside.
Sorry, but this is not correct.
If Black tenukies, White can make a seki on the next move.
Here is the full analysis:
- Black A is the correct answer. Kills immediately and leaves a dead ‘T’ shape inside.
- Black B also kills. However, White can later threaten to play at A which forces Black to capture. This can be used as a Ko threat.
- Black C creates a Seki.
- If Black tenuki, then White A creates a Seki. That means Black cannot ignore this position.
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For example, from Black vs. White , White plays one of the
circled intersections and Black must respond with B5 or C5.
Note the comment (which was from the OP) just before mine, and the “again” in my comment:
Black playing inside again, would be after Black stopped White from making seki.
Oh, I see. My bad.
The analysis part still stands, though, for the benefit of the OP.
Thanks everyone, unfortunately i still don’t understand why A is considered killing the white group. It still seems like seki to me (same with B). If you could explain why the moves are different from C it would really help me. Otherwise, a link to a reference for me to check could help as well. Thank you!
The difference is, the shape of White’s eyespace after White captures Black’s inside stones.
A+B forms a Bulky Five, Bulky Five at Sensei's Library
whereas A+C and B+C are each living eye-shapes.
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For those who want to try this puzzle in an interactive mode.
No solution provided, so every move is considered wrong (but you can safely ignore that).
Edit: provided two solutions (one correct, one incorrect).
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The correct solution you provided is the objectively-not-best killing move 
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Ok thank you everyone, I understand now.
okay what solution did i miss?
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Solve easier problems (with smaller nakade for example). Then come back to this one.
Life and death problems of similar difficulty:
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Thank you! so far these are way too difficult for me 
So i guess I need to start easier. I am reading up on some topics and solving easier puzzles for now, but my next goal will be to solve the ones you linked with some confidence.
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