@article{DE_1997_33_2_a1,
     author = {A. K. Demenchuk},
     title = {Necessary and sufficient conditions for the existence of periodic solutions of linear nonhomogeneous {Pfaffian} systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {155--157},
     publisher = {mathdoc},
     volume = {33},
     number = {2},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1997_33_2_a1/}
}