@article{DAN_1976_226_4_a3,
     author = {V. V. Velichenko},
     title = {On sufficient conditions for optimality for multisheeted fields of extremals},
     journal = {Doklady Akademii Nauk},
     pages = {757--760},
     publisher = {mathdoc},
     volume = {226},
     number = {4},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1976_226_4_a3/}
}