@article{DE_1980_16_6_a7,
     author = {L. T. Ashchepkov and O. V. Vasiliev and I. L. Kovalenok},
     title = {A strong optimality condition for singular controls in a {Goursat--Darboux} system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1054--1059},
     publisher = {mathdoc},
     volume = {16},
     number = {6},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_6_a7/}
}