Proceedings of the 9th national conference on algebra held at the University of Cluj-Napoca, Romania, September 18-20, 1991. Cluj-Napoca: Univ. Cluj-Napoca, Fac. of Math. and Computer Science, “Babeş- Bolyai” Univ., Fac. Math. Comput. Sci. Res. Semin., Prepr. 1992(1), 13-16 (1992).