@article{DE_1971_7_7_a11,
     author = {G. N. Yakovlev},
     title = {Differential properties of the extremals of quadratic functionals with discontinuous coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1288--1293},
     publisher = {mathdoc},
     volume = {7},
     number = {7},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1971_7_7_a11/}
}