@article{DE_1968_4_6_a4,
     author = {R. Gabasov},
     title = {The optimality of singular controls},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1000--1011},
     publisher = {mathdoc},
     volume = {4},
     number = {6},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_6_a4/}
}