KREISS, Hans-otto. Über sachgemäße Cauchyprobleme. Mathematica Scandinavica, Berkeley, CA, United States, v. 13, p. 109–128, 1963. DOI: 10.7146/math.scand.a-10694. Disponível em: https://journals.msp.org/mscand/article/view/2626. Acesso em: 25 jul. 2026.