@article{DMGT_1998_18_2_a7,
     author = {Haviar, Alfonz and Nedela, Roman},
     title = {On varieties of graphs},
     journal = {Discussiones Mathematicae. Graph Theory},
     pages = {209--223},
     publisher = {mathdoc},
     volume = {18},
     number = {2},
     year = {1998},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/DMGT_1998_18_2_a7/}
}