@article{DE_1970_6_6_a4,
     author = {P. E. Tovstik},
     title = {Integrals of a linear equation of order $m+n$ with a small parameter multiplying the derivatives},
     journal = {Differencialʹnye uravneni\^a},
     pages = {989--999},
     publisher = {mathdoc},
     volume = {6},
     number = {6},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_6_a4/}
}