@article{IM2_1986_26_1_a4,
     author = {V. I. Kazimirov and V. I. Plotnikov and I. M. Starobinets},
     title = {An~abstract scheme for the method of variations and necessary conditions for an extremum},
     journal = {Izvestiya. Mathematics },
     pages = {133--151},
     publisher = {mathdoc},
     volume = {26},
     number = {1},
     year = {1986},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1986_26_1_a4/}
}