Just a nobi appears to be enough to prevent connection, even if it makes the empty triangle. --gnostic?
It looks like black can at least get a ko here. --gnostic?
Herman: at and there is no ko.
gnostic?: I guess I miscounted liberties. Do you have a solution to this problem Herman?
ThorAvaTahr: Let me speak for Herman and tell you that he has the solution for it. The hint is: the problem text is a little bit misleading. I would even evaluate the situation as "black can't connect", but that probably depends on the board situation.
gnostic? Well, MadLab seems to agree with you on that point. My Chinese edition of this work in SGF format says this is a "fa yang lun" problem, which I think means this comes from the Igo Hatsuyoron. I found a few lines where black was able to make life by threatening to connect out, but did not attempt a refutation for any of them. I think the key to solving the problem this way is that If you start the problem with a black stone on E 16 or or D 17, then connecting out works (or at least it seems to. I'm more confident of that when there's a stone on E 16). I'm not sure about my ability to solve this kind of problem, so I'll come back to it. I think someone knowledgeable should confirm whether or not this is an Igo Hatsuyoron problem so we can add a link to the appropriate page in that series, and we should change the problem text to something like, "Black to connect out or live" or even "Black to connect out (or not)", because strictly speaking this problem is not a "connecting under" problem.
Herman: Here is one line. This is overly simplistic, of course. is uninspired. What if white plays directly? So yes, the problem statement of "Black to play and connect underneath" isn't really correct. Making life is also acceptable.
This doesn't work either. Could ko be the answer? --gnostic?
This one doesn't work either, but it might be illustrative of the problem in general. I think that in the correct variation, 2 must somehow be short of liberties.