Contra Lam (2014a), the semantics of an A-NOT-A question is also multidimensional in that it has a primary question meaning as well as a secondary assertion meaning which indicates lack of 'anticipation of prior expectationrejection shift'.
a-NOT-a questions are anti-bias questions, thus cannot be used in biased contexts, while aa4 questions are simple questions which can be pragmatically rendered into biased questions in biased contexts.