@article{DAN_1991_316_5_a7,
     author = {A. I. Tret'yak},
     title = {Necessary conditions for optimality of even order in a},
     journal = {Doklady Akademii Nauk},
     pages = {1058--1060},
     publisher = {mathdoc},
     volume = {316},
     number = {5},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_316_5_a7/}
}