@article{DE_1989_25_9_a6,
     author = {A. I. Korotkii},
     title = {On the extension of extremal problems that are connected with controllable elliptic systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1518--1522},
     publisher = {mathdoc},
     volume = {25},
     number = {9},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_9_a6/}
}