@article{DE_1970_6_5_a11,
     author = {N. T. Pham},
     title = {Boundary value problems for natural differential operators on manifolds},
     journal = {Differencialʹnye uravneni\^a},
     pages = {877--888},
     year = {1970},
     volume = {6},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_5_a11/}
}