@article{SM_1969_7_1_a2,
     author = {B. T. Polyak},
     title = {Semicontinuity of integral functionals and existence theorems on extremal problems},
     journal = {Sbornik. Mathematics},
     pages = {59--77},
     publisher = {mathdoc},
     volume = {7},
     number = {1},
     year = {1969},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1969_7_1_a2/}
}