@article{DE_1988_24_12_a4,
     author = {\`E. I. Grudo},
     title = {Necessary and sufficient conditions for the existence of periodic solutions of linear inhomogeneous periodic {Pfaffian} systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2052--2056},
     publisher = {mathdoc},
     volume = {24},
     number = {12},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_12_a4/}
}