1. T. Kato, Perturbation Theory of Linear Operators, Berlin-Heidelberg-New York, Springer Verlag, (1966).
2. M. Reed, B. Simon, Methods of Modern Mathematical Physics, Vols. 1–4, Academic Press, (1970–79).
3. F. Treves, Basic linear partial differential equations, Academic Press (1975).
4. P. Deift, W. Hunziker, B. Simon, E. Vock, Pointwise bounds on eigenfunctions and wave packets in N-body quantum systems IV, Commun. Math. Phys. 64, 1 (1978).
5. W. Hunziker, Helv. Phys. Acta 39, 451 (1966),