@article{DE_1994_30_10_a21,
     author = {F. G. Maksudov and Z. I. Ismailov},
     title = {Normal extensions of second-order differential operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1823--1824},
     publisher = {mathdoc},
     volume = {30},
     number = {10},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1994_30_10_a21/}
}