@article{DE_1973_9_7_a4,
     author = {Yu. I. Zubko and V. A. Tyshkevich},
     title = {On the question of the positivity of a {Cauchy} function},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1207--1213},
     publisher = {mathdoc},
     volume = {9},
     number = {7},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_7_a4/}
}