1. K. JÖRGENS and J. WEIDMANN, Spectral Properties of Hamiltonian Operators, Lecture Notes in Mathematics, 313, Springer (1973).
2. A.M. ERMOLAEV, Vestn. Leningrad Univ., 14, no 22, p 46 (1958).
3. V.A. FOCK, Izvestia Akademii Nauk SSSR, Ser. Fiz, 18, p 1961 (1954). Traduction anglaise: D. Kngl. Norske Videnskab Selsk. Forh. 31, p. 138 (1958).
4. T. KATO, Some Mathematical Problems in Quantum Mechanics, Progress of Theoretical Physics, Supplement no 40 (1967).-Trans. Amer. Math. Soc. 70, p. 212 (1951).
5. J. LERAY, 6ème Congrès du Groupement de mathématiciens d'expression latine, p. 179–189, Gauthier-Villars (1982)