%0 Journal Article
%T Joint sessions of the Petrovskii Seminar on differential equations and mathematical problems of physics and of the Moscow Mathematical Society (twelfth meeting, 18--21 January~1989)
%J Trudy Matematicheskogo Instituta imeni V.A. Steklova
%D 1989
%P 173-202
%V 44
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/RM_1989_44_4_a5/
%G en
%F RM_1989_44_4_a5