@article{DAN_1973_212_3_a10,
     author = {G. Sh. Fridman},
     title = {Radially critical directed graphs},
     journal = {Doklady Akademii Nauk},
     pages = {565--568},
     publisher = {mathdoc},
     volume = {212},
     number = {3},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1973_212_3_a10/}
}