%0 Journal Article
%A L. A. Sakhnovich
%T Necessary conditions for the existence of a~transformation operator for fourth-order equations
%J Trudy Matematicheskogo Instituta imeni V.A. Steklova
%D 1961
%V 16
%N 5
%I mathdoc
%U http://geodesic.mathdoc.fr/item/RM_1961_16_5_a13/
%G ru
%F RM_1961_16_5_a13