@article{DAN_1988_300_3_a15,
     author = {Ya. N. Fel'd},
     title = {A criterion for the realizability of direction diagrams by},
     journal = {Doklady Akademii Nauk},
     pages = {583--587},
     publisher = {mathdoc},
     volume = {300},
     number = {3},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1988_300_3_a15/}
}