@article{PIM2_1989__45(59)_257835,
     author = {Jankovi\'c, Vladimir},
     title = {Necessary conditions in a problem of calculus of variations.},
     journal = {Publications de l 'Institut Math\'ematique. Nouvelle S\'erie},
     pages = {143},
     publisher = {mathdoc},
     volume = {45(59)},
     year = {1989},
     zbl = {0681.49019},
     language = {en},
     url = {https://geodesic-test.mathdoc.fr/item/PIM2_1989__45(59)_257835/}
}