1. A. Einstein, Ann. Phys. (Leipzig) ,4th Ser. 17, 132–148 (1905).
2. See, e.g., H. Paul, Wiss. Fortschr. 29, 62 (1979).
3. M. Lax and M. Zwanziger, Phys. Rev. A 7, 750–771 (1973).
4. P. A. M. Dirac, Quantum Mechanics ,4th Ed. (Clarendon Press, Oxford, 1958).
5. A. O. Barut, Z. Naturforsch. 33a, 993–994 (1978).