1. Arp, H.: 1970, Astron. J. 75, 1.
2. Arp, H.: 1973, in George Field (ed.), The Redshift Controversy, Publ. Benjamin Press.
3. Arp, H.: 1974, in J. R. Shakeshaft (ed.), ‘The Formation and Dynamics of Galaxies’, IAU Symposium
58, 199.
4. Burbidge, E. M., Burbidge, G. R., Solomon, P. M., and Strittmatter, P. A.: 1971, Astrophys. J.
170, 233.
5. Barbierie, C. Battistini, P., and Nasi, E.: 1967, Publ Obs. Astron. Padova, No. 141.