@article{DE_1990_26_8_a20,
     author = {B. M. Usifov and Z. A. Karagezov},
     title = {On the problem of the existence of optimal controls},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1437--1441},
     publisher = {mathdoc},
     volume = {26},
     number = {8},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_8_a20/}
}