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The atari at 9 allows B to cut off 8. Playing 6 at 10 allows 7 at 6, cutting off the white stones as well.
The atari at 'a' again forces white to connect at the marked stone, allowing black 'b' to kill off the white cutting stone.
3 @ the marked black stone. Playing 1 on the other side still fails, as W cannot bridge under due to a connect-and-die.
Let's examine other responses.
Easy variation for 6: a and b are miai to save 1 and sever the chain of W stones connected to 4. The continuations are given:
Little more complicated variation for 6. Pushing with 9 is key; if W plays a instead of blocking at 10, B connects underneath with 11 at 10.
If W insists on cutting B off by playing through 4, B returns the favor at 5, triggering a race. However, W only has 3 liberties to B's 5 or more. W cannot escape. 2 at 4 leads to 3 at 'a', postponing the inevitable.
unkx80: I am not sure about your claim that Black has at least 5 liberties. It seems to me that and causes Black to have only 2 liberties.
After B at 'a', W at 'b', B at 'c', d and e are miai to trigger the capturing race, reverting to previous diagrams.
B sacrifices the marked stones to prevent W connecting at 'a'. If W connects at a, B at b is atari and W's position collapses.
If W hanes to the right, a and b are miai to cut off at least 1 white stone, ensuring the connection
If W hanes to the left, 3 and the response at 4 play out slightly differently; now a and b are miai for black to cut, and b and c are miai for black to save the cutting stones. W's only hope is to play b.
If 4 here, this sequence follows. @ a, @ marked stone, @ b, cutting off . I believe the 7-8 exchange can be omitted, but I don't see why B would do that.
elvard: I've found this as solution. Idea is already in previous attempts, just everytime there is one or more unnecessary moves.
is the solution. It's sort of asking move, waiting for white's response at 'a' or 'b' and then deciding the proper connect underneath technique. NOTE: Exchange of Black 'c' for White 'd' is not required since it doesn't add or take a liberty of white group.
The draw back at is essential as it prepares for 'a' followed by white connect at 'b' which tooks him off one liberty.