@article{DE_1980_16_8_a9,
     author = {I. T. Skorodinskii},
     title = {Investigation of the third variation of a functional on singular controls},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1438--1444},
     publisher = {mathdoc},
     volume = {16},
     number = {8},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_8_a9/}
}