@article{DAN_1965_160_2_a9,
     author = {A. I. Fet},
     title = {On a periodicity problem in the calculus of variations},
     journal = {Doklady Akademii Nauk},
     pages = {287--289},
     publisher = {mathdoc},
     volume = {160},
     number = {2},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1965_160_2_a9/}
}