“…We notice that the form a is bilinear, continuous and coercive on the kernel of b, and b is bilinear, continuous, and satisfies the inf-sup condition; see, e.g., [8,18,24]. Hence, problem (6)- (9) is well-posed (provided that k 2 is not an interior Maxwell eigenvalue) and there is a positive constant C, depending on Ω and k 2 , such that…”