@article{SLC_2005-2007_55_a2,
     author = {S. Pirzada and U. Samee},
     title = {Mark {Sequences} in {Digraphs}},
     journal = {S\'eminaire lotharingien de combinatoire},
     publisher = {mathdoc},
     volume = {55},
     year = {2005-2007},
     url = {http://geodesic.mathdoc.fr/item/SLC_2005-2007_55_a2/}
}