Markosyan, S. E., and A. H. Khachaturyan. “OPTIMAL LEVEL PLACEMENT OF THE TRANSITIVE ORIENTED AND BIPARTITE ORIENTED GRAPHS BY HEIGHT”. Proceedings of the YSU A: Physical and Mathematical Sciences, vol. 43, no. 2 (219), June 2009, pp. 43-49, doi:10.46991/PYSU:A/2009.43.2.043.