1. Combes, J. M.: Nuovo Cimento64A, 111 (1969)
2. Deift, P., Simon, B.: Commun. Pure Appl. Math., to appear
3. Deift, P., Hunziker, W., Simon, B., Vock, E.: ETH Preprint, in preparation
4. Kuroda, S.: J. Math. Phys.3, 933 (1962)
5. Reed, M., Simon, B.: Methods of modern mathematical physics, Vol. III. Scattering theory. New York: Academic Press 1978