@article{10_37236_1579,
     author = {Zden\v{e}k Dvo\v{r}\'ak and Daniel Kr\'al'},
     title = {On planar mixed hypergraphs},
     journal = {The electronic journal of combinatorics},
     year = {2001},
     volume = {8},
     number = {1},
     doi = {10.37236/1579},
     zbl = {1021.05032},
     url = {http://geodesic.mathdoc.fr/articles/10.37236/1579/}
}