1. Alekseev V.A.: 1993, in Propagation Effects in Space VLBI, Proceedings of the Workshop, Leningrad, 1990, ed(s)., L.I.Gurvits, National Astronomy and Ionosphere Center, 123
2. Andreyanov V.V. et al.: 1984, Proc. of the ESA Workshop on QUASAT Project ESA SP-213
3. Braginsky V.B. et al.: 1992, in Astrophysics on the Threshold of the 21st Century, ed(s)., N.S.Kardashev, Gordon & Breach Sci. Publishers: Philadelphia, 315
4. Gurvits L.I., Pogrebenko S.V.: 1985, Astrophys. Space Sci. 112, 337
5. Gurvits L.I.: 1993, in These Proceedings, ed(s)., J.G.Robertson and W.J.Tango, Kluwer Academic Publishers: Dordrecht, in press