1. Bakos, G. A. and Heard, J. F.: 1958,Astrophys. J. 63, 302.
2. Catalona, S., Frisina, A., Rodono, M., and Scaltriti, F.: 1978,Inf. Bull. Var. Stars, No. 1427.
3. Eaton, J. A.: 1977,Inf. Bull. Var. Stars, No. 1297.
4. Eaton, J. A. and Hall, D. S.: 1979,Astrophys. J. 227, 907.
5. Hall, D. S.: 1976, in W. S. Fitch (ed.), ?Multiply Periodic Phenomena in Variable Stars?,IAU Colloq. 29, Pt. 1.