@article{DE_1975_11_2_a4,
     author = {K. A. Dib},
     title = {A criterion for small change in the direction of the solutions for $n$th order linear differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {246--254},
     publisher = {mathdoc},
     volume = {11},
     number = {2},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1975_11_2_a4/}
}