Markosjan, S. E. and Karapetjan, I. "Perfect Graphs." Doklady Akademiya Nauk Armyanskoĭ SSR63, 292-296, 1976.Meyniel, H. "On the Perfect Graph Conjecture." Disc. Math.16, 339-342, 1976.Sloane, N. J. A. Sequence A123434 in "The On-Line Encyclopedia of Integer Sequences."