Twisted four in the corner
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If is tenuki, then at kills. After , White can finish the ko by filling at . If Black has no outside liberties, then would be better, since filling at would leave a ko threat. After Black retakes the ko with , Black can finish the ko with to live with full points. (The same applies if is tenuki.)
If there are at least two outside liberties, Black is alive with three points. (Three points instead of four because Black eventually needs a reinforcing move inside when White fills up one of the outside liberties.)
However, the indicated lines might be better than filling immediately, since in both indicated lines, and and each threaten to kill outright, rather than just threatening a ko to kill.