HOFFMANN, Udo. On the Complexity of the Planar Slope Number Problem. Journal of Graph Algorithms and Applications, [S. l.], v. 21, n. 2, p. 183–193, 2017. DOI: 10.7155/jgaa.00411. Disponível em: https://jgaa.info/index.php/jgaa/article/view/paper411. Acesso em: 30 jun. 2024.