1. Abia, C; Rebolo, R.: 1990, Ap.J. (In press).
2. Alcock, C; Fuller, G.M.; Matthews, G.J.: 1987, Ap. J., 320, 489.
3. Applegate, J.H.; Hogan, C.J.; Scherrer, R.J.: 1988, Ap. J., 329, 592.
4. Bardeen, J.M.; Bond, J.R.; Efstathiou, G.: 1987, Ap. J., 321, 28.
5. Beckman, J.E.; Abia, C; Rebolo, R.: 1989, Asirophys. Spa. Sci. (In press).