WINZELL, B. Sub-elliptic estimates for the oblique derivative problem. MATHEMATICA SCANDINAVICA, [S. l.], v. 43, p. 169–176, 1978. DOI: 10.7146/math.scand.a-11772. Disponível em: https://www.mscand.dk/article/view/11772. Acesso em: 4 may. 2024.