E. M. ELKHOLY; A. SAKR; H. AHMED. Folding of Digraphs. International Journal of Mathematics And its Applications, [S. l.], v. 3, n. 3 - D, p. 13–17, 2015. Disponível em: http://ijmaa.in/index.php/ijmaa/article/view/471. Acesso em: 12 may. 2024.