Alex’s counterexample as stated is not a counterexample to Q4, since it is in fact concave.
I believe your counterexample violates A5, taking B=¬X, A=X, and p=12.
Seems right, oops! A5 is here saying that if any part of my u is flat it had better stay flat!
I think I can repair my counterexample but looks like you’ve already found your own.
Alex’s counterexample as stated is not a counterexample to Q4, since it is in fact concave.
I believe your counterexample violates A5, taking B=¬X, A=X, and p=12.
Seems right, oops! A5 is here saying that if any part of my u is flat it had better stay flat!
I think I can repair my counterexample but looks like you’ve already found your own.