WINZELL, Bengt. 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://tidsskrift.dk/math/article/view/11772. Acesso em: 14 aug. 2026.