@article{DE_1975_11_9_a16,
     author = {U. Engelmann},
     title = {A problem with nonlocal boundary conditions for second order hyperbolic partial operator-differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1687--1693},
     publisher = {mathdoc},
     volume = {11},
     number = {9},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1975_11_9_a16/}
}