1. M. V. Berry and E. C. Sinclar, J. Phys. A 30, 2853 (1997).
2. M. V. Berry, Proc. R. Soc. Lond. A 452, 1207 (1996).
3. V. B. Berestetskii, E. M. Lifshits, and L. P. Pitaevskii, Course of Theoretical Physics, Vol. 4: Quantum Electrodynamics (Nauka, Moscow, 1989; Pergamon, Oxford, 1982).
4. S. Chandrasekhar, The Mathematical Theory of Black Holes (Clarendon, Oxford, 1980; Moscow, 1986).
5. V. V. Petkevich, Theoretical Mechanics (Nauka, Moscow, 1971) [in Russian].