All you need to know about Carpenter's Square - 29
We've seen very similar patterns while studying Shape 23 and 24. Just to repeat here to make the series complete.
is clearly the only move. is the best answer. is also the only correct move. The result is a ko.
is a poor answer. It's never a good idea to reduce your own eyespace. The corner is dead.
here is incorrect. is good. The corner would end up in seki.
Conclusion: Diagram 29.2 is the best sequence for both sides.