@article{DE_1978_14_4_a6,
     author = {G. N. Petrovskiǐ},
     title = {The construction of coefficient tests for the $G$-orthogonal reducibility and $G$-spherical compatibility of systems of linear differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {637--645},
     publisher = {mathdoc},
     volume = {14},
     number = {4},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1978_14_4_a6/}
}