@article{ARM_1989_25_1-2_a6,
     author = {Hell, Pavol and Ne\v{s}et\v{r}il, Jaroslav},
     title = {Universality of directed graphs of a given height},
     journal = {Archivum mathematicum},
     pages = {47--54},
     year = {1989},
     volume = {25},
     number = {1-2},
     mrnumber = {1189198},
     zbl = {0712.05033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1989_25_1-2_a6/}
}