@article{DMGT_2007_27_3_a16,
     author = {Imrich, Wilfried and Kl\"ockl, Werner},
     title = {Factoring directed graphs with respect to the cardinal product in polynomial time},
     journal = {Discussiones Mathematicae. Graph Theory},
     pages = {593--601},
     publisher = {mathdoc},
     volume = {27},
     number = {3},
     year = {2007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/DMGT_2007_27_3_a16/}
}