JAKOBSEN, Ivan Tafteberg. On a certain homomorphism properties of graphs II. Mathematica Scandinavica, Berkeley, CA, United States, v. 52, p. 229–261, 1983. DOI: 10.7146/math.scand.a-12004. Disponível em: https://journals.msp.org/mscand/article/view/1618. Acesso em: 25 jul. 2026.