%0 Journal Article
%A Le Khyu Zien
%A V. I. Shevchenko
%T Homotopy classification of systems in the plane that are elliptic in the sense of Douglis and Nirenberg
%J Doklady Akademii Nauk
%D 1979
%P 824-827
%V 244
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1979_244_4_a7/
%G ru
%F DAN_1979_244_4_a7