1. J. M. Cook: Convergence to the Moller wave matrix. J. Math. Phys. 3 (1957), 82–87.
2. T. Ikebe: Eigenfunction expansions associated with the Schrödinger operator and their applications to scattering theory. Arch. Rational Mech. Anal. 5 (1960), 1–35.
3. J. M. Jauch: Theory of the scattering operator. Heiv. Phys. Acta 31 (1958), 127–158.
4. T. Kato: Perturbation theory for linear operators. Springer, Berlin, 1966.
5. T. Kato and S. T. Kuroda: A remark on the unitarity property of the scattering operator. Nuovo Cimento 14 (1959), 1102–1107.