Bifurcation in mathematical models of social and economic interaction. (English). In: Greguš, Michal (ed.): Equadiff 5. Proceedings of the Fifth Czechoslovak Conference on Differential Equations and Their Applications held in Bratislava, August 24-28, 1981. BSB B.G. Teubner Verlagsgesellschaft, Leipzig, 1982. pp. 324-328