TEXTORIUS, Björn. Minimaxprinzipe zur Bestimmung der Eigenwerte $J$-nichtnegativer Operatoren. Mathematica Scandinavica, Berkeley, CA, United States, v. 35, p. 105–114, 1974. DOI: 10.7146/math.scand.a-11538. Disponível em: https://journals.msp.org/mscand/article/view/2107. Acesso em: 25 jul. 2026.