@article{DAN_1969_184_6_a1,
     author = {F. P. Vasil'ev},
     title = {Optimality conditions for certain classes of systems which are not solved with respect to the derivative},
     journal = {Doklady Akademii Nauk},
     pages = {1267--1270},
     publisher = {mathdoc},
     volume = {184},
     number = {6},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_184_6_a1/}
}