“…Hence, new tools are necessary for the analysis of the corresponding optimal control problems. It should be emphasized here that boundary value problems for degenerate elliptic and parabolic equations have received a lot of attention in the last years (see, for instance, [5,6,9,23,24,26]). As for the control issue for degenerate wave equations, we already mentioned [1,14] (see also [20] for the sensitivity analysis of optimal control problems for wave equations in domain with defects).…”