@article{DAN_1968_180_4_a4,
     author = {A. D. Ioffe and V. M. Tikhomirov},
     title = {Duality in problems of the calculus of variations},
     journal = {Doklady Akademii Nauk},
     pages = {789--792},
     publisher = {mathdoc},
     volume = {180},
     number = {4},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_180_4_a4/}
}