%0 Journal Article %A I. M. Gel'fand %A I. S. Zakharevich %T Spectral theory of a pencil of skew-symmetric differential operators of third order on $S^1$ %J Funkcionalʹnyj analiz i ego priloženiâ %D 1989 %P 1-11 %V 23 %N 2 %I mathdoc %U http://geodesic.mathdoc.fr/item/FAA_1989_23_2_a0/ %G ru %F FAA_1989_23_2_a0