@article{DE_1989_25_8_a5,
     author = {A. V. Savkin},
     title = {Frequency criteria for the stability and instability of linear periodic systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1332--1339},
     year = {1989},
     volume = {25},
     number = {8},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_8_a5/}
}