AVAKUMOVIC, Vojislav G. Über die Eigenwerte der Schwingungsgleichung. Mathematica Scandinavica, Berkeley, CA, United States, v. 4, p. 161–173, 1956. DOI: 10.7146/math.scand.a-10467. Disponível em: https://journals.msp.org/mscand/article/view/2856. Acesso em: 25 jul. 2026.