@article{DE_1973_9_7_a2,
     author = {N. I. Vasilyev and Yu. A. Klokov},
     title = {The solvability of boundary value problems in the small},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1187--1194},
     year = {1973},
     volume = {9},
     number = {7},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_7_a2/}
}