ASPLUND, E.; GRÜNBAUM, B. On a Coloring Problem. MATHEMATICA SCANDINAVICA, [S. l.], v. 8, p. 181–188, 1960. DOI: 10.7146/math.scand.a-10607. Disponível em: https://www.mscand.dk/article/view/10607. Acesso em: 2 may. 2024.