MARKSJÖ, B.; TEXTORIUS, B. On the Stability of Linear Differential Equations in Spaces with an Indefinite Metric. MATHEMATICA SCANDINAVICA, [S. l.], v. 20, p. 177–192, 1967. DOI: 10.7146/math.scand.a-10829. Disponível em: https://www.mscand.dk/article/view/10829. Acesso em: 1 may. 2024.