@article{DE_1974_10_2_a9,
     author = {G. N. Petrovskiǐ},
     title = {Certain properties of generalized $\phi$-invariant systems of linear differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {258--264},
     publisher = {mathdoc},
     volume = {10},
     number = {2},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1974_10_2_a9/}
}