THOMÉE, Vidar. Estimates of the Friedrichs-Lewy type for mixed problems in the theory of linear hyperbolic differential equations in two independent variables. Mathematica Scandinavica, Berkeley, CA, United States, v. 5, p. 93–113, 1957. DOI: 10.7146/math.scand.a-10493. Disponível em: https://journals.msp.org/mscand/article/view/2830. Acesso em: 25 jul. 2026.