@article{DE_1999_35_4_a17,
     author = {I. Tabov and D. Kolev},
     title = {Obstacles to the propagation of simple waves in a nonhomogeneous medium},
     journal = {Differencialʹnye uravneni\^a},
     pages = {570--572},
     publisher = {mathdoc},
     volume = {35},
     number = {4},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_4_a17/}
}