@article{DE_1980_16_6_a0,
     author = {\`E. I. Grudo},
     title = {A differential system with two purely imaginary roots of a characteristic equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {963--979},
     publisher = {mathdoc},
     volume = {16},
     number = {6},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_6_a0/}
}