@article{DE_1989_25_6_a0,
     author = {P. A. Golovach},
     title = {A topological invariant in pursuit problems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {923--929},
     publisher = {mathdoc},
     volume = {25},
     number = {6},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_6_a0/}
}