@article{DAN_1969_184_4_a2,
     author = {V. I. Gorbachuk and M. L. Gorbachuk},
     title = {Expansion in the eigenfunctions of second order differential equation with operator coefficients},
     journal = {Doklady Akademii Nauk},
     pages = {774--777},
     publisher = {mathdoc},
     volume = {184},
     number = {4},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_184_4_a2/}
}