@misc{RM_1990_45_4_a2,
     title = {Joint sessions of the {Petrovskii} {Seminar} on differential equations and mathematical problems of physics and the {Moscow} {Mathematical} {Society} {(Thirteenth} session, 2--5 {February~1990)}},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {127--155},
     publisher = {mathdoc},
     volume = {45},
     number = {4},
     year = {1990},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1990_45_4_a2/}
}