Does the 3-3 invasion under this unconventional 4-4 enclosure lead to ko, or can black kill unconditionally?
I believe that W can live or escape unconditionally. The strongest threats to W would seem to be at a, b, and c. None of those lines seem to lead to an unconditional kill, or even a ko to kill.
tapir: As always all comments without warranty. I don't see how White is going to live unconditionally in the corner after b. However White does not need to live there.
If at , then Black connects at . White is running with no base. Better to probe at or a without the / exchange.
Is performing any useful function? The triangle is empty. W has 'c' to look forward to later as well. This is an inverted move order for @ to start.
Question has been raised: what about probing at a or b before the 3-3 invasion? How does that play out?
Herman: The standard idea after would probably be , after which there are several options.
Herman: With moves like this, black can reduce white to only one (potential) eye in the corner, but white has escaped, so black should have a clear plan to continue the attack.
Herman: blocking on this side allows life, because forces . Black should of course keep in reserve.
Herman: White can answer with . is required, otherwise White will play there. The makes life, because a is still sente for white.
-- thanks for this, I missed that obvious move.