@article{DA_1980_20_a0,
     author = {L. T. Ashchepkov},
     title = {Singular extremals of discontinuous control {systems.~I}},
     journal = {Diskretnyj analiz i issledovanie operacij},
     pages = {3--13},
     publisher = {mathdoc},
     number = {20},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DA_1980_20_a0/}
}