1. Anderson, N., Kunth, D. and Sargent, W.L.W.: 1988,Astron. J. 95, 644.
2. Arp, H.: 1984,Astrophys. J. 185, 547.
3. Barbieri, C. and Chu, Y.: 1986, in: G. Swarup and V.K. Kapahi (eds.),Quasar, p. 51.
4. Barbieri, C.et al.: 1986,Astron. Astrophys. Suppl. 67, 551.
5. Boyle, B.J., Fonk, R. and Shanks, T.: 1983, in:Quasars and Gravitational Lenses, 24th Liège Internat. Astrophys. Coll., p. 368.