KREISS, H.- otto. Über sachgemäße Cauchyprobleme. MATHEMATICA SCANDINAVICA, [S. l.], v. 13, p. 109–128, 1963. DOI: 10.7146/math.scand.a-10694. Disponível em: https://www.mscand.dk/article/view/10694. Acesso em: 3 may. 2024.