Alavi, Yousef (ed.) et al., Graph theory, combinatorics, and applications, Vol. 2. Proceedings of the sixth quadrennial international conference on the theory and applications of graphs held at Western Michigan University, Kalamazoo, MI, USA, May 30-June 3, 1988. New York: John Wiley & Sons, Inc. Wiley-Interscience Publication. 639-644 (1991).
Onishchik, A. L. (ed.), Questions of group theory and homological algebra. Collection of scientific works. Yaroslavl’: Yaroslavskij Gosudarstvennyj Universitet. 166-167 (1991).
Jacob, Gérard (ed.) et al., Algebraic computing in control. Proceedings of the first European conference, Paris, France, March 13-15, 1991. Berlin: Springer-Verlag. Lect. Notes Control Inf. Sci. 165, 178-190 (1991).