1. V. N. Shapovalov, Izv. VUZ. Fizika [Soviet Physics Journal], (in press).
2. P. A. M. Dirac, Principles of Quantum Mechanics [Russian translation], Fizmatgiz, 1960.
3. V. N. Shapovalov and V. N. Korobov, Izv. VUZ. Fizika [Soviet Physics Journal], no. 7, 1967.