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, [S. l.], v. 5, p. 93–113, 1957. DOI: 10.7146/math.scand.a-10493. Disponível em: https://tidsskrift.dk/math/article/view/10493. Acesso em: 13 aug. 2026.