@article{DAN_1970_193_4_a4,
     author = {G. A. Leonov},
     title = {The necessity of a frequency condition for the absolute stability of stationary systems in the critical case of a pair of pure imaginary roots},
     journal = {Doklady Akademii Nauk},
     pages = {756--759},
     year = {1970},
     volume = {193},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_193_4_a4/}
}