“…We note some related works on inverse problems for hyperbolic equations that make use of Carleman estimates: Bellassoued [1], Bukhgeim [2], Imanuvilov and Yamamoto [8] - [11], Isakov [12], [14], [15], Isakov and Yamamoto [16], Klibanov [17], Klibanov and Timonov [18], Klibanov and Yamamoto [19], Romanov [24], Yamamoto [25] and the references therein. As for available Carleman estimates, see Fursikov and Imanuvilov [5], Hörmander [6], Imanuvilov [7], Isakov [13], Lavrent'ev, V.G.…”