threatens to make life in the corner, while creating approaches to the existing liberties. If Black threatens the connect-and-die at 3, White simply blocks, and is a necessary approach move, allowing White to win the semeai (which then stands at 2 liberties each).
If Black plays at directly here, w should answer at 3. B is captured. w3 has the andvantage in later Kos over anny other way to capture. Should b play atari as a Kothreat and w ignores, the dammage is smaller.
looks like the right way to exploit the shape, by analogy with problem 4, but after , it seems that the best White can do is to set up a ko.