1. Done, C. et al. in Structure and Emission Properties of Accretion Disks (eds Bertout, C., Collin-Souffrin, S., Lasota, J.-P. & Tran Thanh Van, J.) 417–418 (Editions Frontieres, Gif sur Yvette, 1991).
2. Mittaz, J. P. D. & Branduardi-Raymont, G. Mon. Not. R. astr. Soc. 238, 1029–1046 (1989).
3. Syer, D., Clarke, C. J. & Rees, M. J. Mon. Not. R. astr. Soc. 250, 505–512 (1991).
4. Done, C. et al. in Testing the AGN Paradigm (eds Urry, C. M., Neff, S. & Holt, S.) (AIP Conf. Proc. Series, in the press).
5. Done, C. et al. in Frontiers of X-ray Astronomy (eds Tanaka, Y. & Koyama, K.) (Universal Academy Press, Tokyo, in the press).