@article{DE_1980_16_9_a2,
     author = {\`E. I. Grudo and L. A. Poplavskaya},
     title = {The structure of the solutions of a two-dimensional periodic differential {system.~I}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1559--1580},
     year = {1980},
     volume = {16},
     number = {9},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_9_a2/}
}