@article{DE_1979_15_6_a13,
     author = {Ya. A. Roitberg and Z. G. Sheftel},
     title = {Optimal control of systems described by general elliptic problems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1075--1087},
     publisher = {mathdoc},
     volume = {15},
     number = {6},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1979_15_6_a13/}
}