The Motion, evolution of orbits, and origin of comets; symposium no. 45, held in Leningrad, U.S.S.R., August 4-11, 1970. - Chebotarev, G. A. (Gleb Aleksandrovich); Kazimirchak-Polonskaia, E. I; Marsden, B. G. (Brian G.) (Reidel, 1972)