@article{DE_1973_9_9_a7,
     author = {N. N. Petrov},
     title = {The boundary of the set of controllability of plane holomorphic systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1618--1626},
     publisher = {mathdoc},
     volume = {9},
     number = {9},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_9_a7/}
}