@article{DE_1977_13_6_a3,
     author = {I. T. Kiguradze},
     title = {The periodic boundary value problem for a two-dimensional differential system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {996--1007},
     publisher = {mathdoc},
     volume = {13},
     number = {6},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_6_a3/}
}