THOMÉE, V. Estimates of the Friedrichs-Lewy type for mixed problems in the theory of linear hyperbolic differential equations in two independent variables. MATHEMATICA SCANDINAVICA, [S. l.], v. 5, p. 93–113, 1957. DOI: 10.7146/math.scand.a-10493. Disponível em: https://www.mscand.dk/article/view/10493. Acesso em: 3 may. 2024.