@article{PIM_1989_N_S_45_59_a21,
     author = {Vladimir Jankovi\'c},
     title = {Necessary {Conditions} in a {Problem} of {Calculus} of {Variations}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {143 },
     year = {1989},
     volume = {_N_S_45},
     number = {59},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PIM_1989_N_S_45_59_a21/}
}