1. Chanan, G., Middleditch, J., and Nelson, J. E.: 1976,Astrophys. J. in press.
2. Kopal, Z.: 1954,Jodrell Bank Ann. 1, 37?57.
3. Kopal, Z.: 1959,Close Binary Systems, Chapman-Hall and John Wiley, London and New York.
4. Kopal, Z.: 1972, inAdvances Astron. Astrophys. Academic Press, New York; vol. 9, pp. 1?65.
5. Kopal, Z.: 1975,Astrophys. Space Sci. 38, 191 (Paper V).