1. A. Abragam, The Principles of Nuclear Magnetism (Clarendon, Oxford, 1961; Inostrannaya Literatura, Moscow, 1963).
2. S. Mukamel, Principles of Nonlinear Optical Spectroscopy (Oxford Univ. Press, Oxford, 1995).
3. D. Forster, Hydrodynamic Fluctuations, Broken Symmetry, and Correlation Functions (Benjamin, Reading, MA, 1975; Atomizdat, Moscow, 1980).
4. P. N. Argyres and P. L. Kelley, Phys. Rev. A 134, 98 (1964).
5. K. Shimizu, R. G. Neuhauser, C. A. Leatherdale, et al., Phys. Rev. B 63, 205316 (2001).