@article{MAN_1960__141_160797,
     author = {K. Wagner},
     title = {Faktorklassen in {Graphen.}},
     journal = {Mathematische Annalen},
     pages = {49--67},
     year = {1960},
     volume = {141},
     zbl = {0091.37603},
     url = {http://geodesic.mathdoc.fr/item/MAN_1960__141_160797/}
}