%0 Journal Article %A K. S. Sibirskii %T Invariants of linear representations of the rotation group of the plane and their applications in the qualitative theory of differential equations %J Differencialʹnye uravneniâ %D 1966 %P 736-751 %V 2 %N 6 %I mathdoc %U http://geodesic.mathdoc.fr/item/DE_1966_2_6_a1/ %G ru %F DE_1966_2_6_a1