@article{NSJOM_2003_33_1a_2,
     author = {S. Pirzada},
     title = {Simple score 

 sequences in oriented graphs},
     journal = {Novi Sad Journal of Mathematics},
     pages = {25-29},
     year = {2003},
     volume = {33},
     number = {1},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_2003_33_1a_2/}
}