JAKOBSEN, I. T. On a certain homomorphism properties of graphs II. MATHEMATICA SCANDINAVICA, [S. l.], v. 52, p. 229–261, 1983. DOI: 10.7146/math.scand.a-12004. Disponível em: https://www.mscand.dk/article/view/12004. Acesso em: 3 may. 2024.