@article{DE_1987_23_9_a6,
     author = {V. N. Pyvovarchyk},
     title = {The discrete spectrum of a problem connected with wave propagation in an inhomogeneous medium with viscous friction},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1533--1538},
     publisher = {mathdoc},
     volume = {23},
     number = {9},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_9_a6/}
}