@article{DE_1973_9_12_a8,
     author = {E. L. Tonkov},
     title = {Disconjugacy and number of switchings in a linear time-optimal nonstationary system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2180--2185},
     publisher = {mathdoc},
     volume = {9},
     number = {12},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_12_a8/}
}