1. M. Reed and B. Simon, ?The scattering of classical waves from inhomogeneous media,? Math. Z.,155, No. 1, 163?180 (1977).
2. M. Reed and B. Simon, Methods of Modern Mathematical Physics, Vol. 3. Scattering Theory [Russian translation], Mir, Moscow (1982).
3. L. D. Faddeev, ?Inverse problem of quantum scattering. II,? Modern Mathematics Problems [in Russian], Vol. 3 (1974), pp. 93?180.
4. P. L. Trudinger, ?The inverse scattering problem for perturbed wave equations,? Arch. Ration. Mech. Anal.,81 No. 3, 245?279 (1983).
5. C. H. Wilcox, ?Scattering theory for d'Alambert equation in exterior domains,? Lect. Notes Math.,442, 117 (1975).