VARTAK, M. N.; NARAYANAN, H. New Proof of 4-Colourability of a Class of Graphs. The Journal of the Indian Mathematical Society, [S. l.], v. 38, n. 1-4, p. 201–205, 1974. Disponível em: http://www.informaticsjournals.com/index.php/jims/article/view/16692. Acesso em: 6 may. 2024.