@article{DE_1987_23_6_a2,
     author = {V. D. Budaev},
     title = {The property of being an unconditional basis on a closed interval, for systems of eigen- and associated functions of a second-order operator with discontinuous coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {941--952},
     publisher = {mathdoc},
     volume = {23},
     number = {6},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_6_a2/}
}