KRISHNAN, Uma; SUNDER, V. S. On Principal Graphs and Weak Duality. MATHEMATICA SCANDINAVICA, [S. l.], v. 74, p. 49–63, 1994. DOI: 10.7146/math.scand.a-12479. Disponível em: https://tidsskrift.dk/math/article/view/12479. Acesso em: 14 aug. 2026.