THOMÉE, Vidar. Existence Proofs for Mixed Problems for Hyperbolic Differential Equations in Two Independent Variables by Means of the Continuity Method. Mathematica Scandinavica, Berkeley, CA, United States, v. 6, p. 5–32, 1958. DOI: 10.7146/math.scand.a-10531. Disponível em: https://journals.msp.org/mscand/article/view/2813. Acesso em: 25 jul. 2026.