1. Afanaseva, V., and P. F. Grudzdev, Opt. Spektrosk.
55, 416 (1983).
2. Afanaseva, V., and P. F. Grudzdev, [Opt. Spectrosc. (USSR) 54, 245 (1983)].
3. Au, C. K., G. Feinberg, and J. Sucher, Phys. Rev. Lett.
53, 1145 (1984).
4. Babb, J. F., and L. Spruch, Phys. Rev. A
36, 456 (1987).
5. Babb, J. F., and L. Spruch, Phys. Rev. A
38, 13 (1988).