@article{DE_1985_21_5_a6,
     author = {Yu. A. Mitropol'skii and A. M. Samoilenko and V. L. Kulik},
     title = {Application of quadratic forms to the study of systems of linear differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {776--788},
     publisher = {mathdoc},
     volume = {21},
     number = {5},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_5_a6/}
}