KRISHNAN, Uma; SUNDER, V. S. On Principal Graphs and Weak Duality. Mathematica Scandinavica, Berkeley, CA, United States, v. 74, p. 49–63, 1994. DOI: 10.7146/math.scand.a-12479. Disponível em: https://journals.msp.org/mscand/article/view/1149. Acesso em: 24 jul. 2026.