“…An example in [3] shows that, in general, ω(·, A, D) = ω(·, A, D) on D. Section 6 and 9 below are devoted to the study of ω(·, A, D) in some important cases. As we will see later, in most applications one can obtain good and simple characterizations of ω(·, A, D) (see Theorem 5, 6, 7, 9 and Corollary 2, 3 below).…”