1. Ehrenfest, P.: Z. Physik45, 455 (1927)
2. Friedrichs, K.O.: Perturbation of spectra in Hilbert space. Providence, RI: Am. Math. Soc. 1965
3. Ginibre, J., Velo, G.: On a class of non linear Schrödinger equations. I. The Cauchy problem, general case; II. Scattering theory, general case. J. Funct. Anal. (in press).
4. Ann. Inst. Henri Poincaré28, 287?316 (1978)
5. Ginibre, J., Velo, G.: (in preparation)