@article{DE_1978_14_6_a1,
     author = {\`E. I. Grudo},
     title = {A differential system with a zero root of the characteristic equation and with periodic coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {974--993},
     publisher = {mathdoc},
     volume = {14},
     number = {6},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1978_14_6_a1/}
}