$a Asteroids, comets, meteors 1993 : proceedings of the 160th Symposium of the International Astronomical Union held in Belgirate, Italy, June 14-18, 1993 / ed. by A. Milani and M. Di Martino, A. Cellino. - Dordrecht, 1994. $b CIP LCC (Milani, Andrea) ; (Dipartimento di Matematica, Universita di Pisa, Italy)