WIDMAN, Kjell-ove. Inequalities for the Green Function and Boundary Continuity of the Gradient of Solutions of Elliptic Differential Equations. Mathematica Scandinavica, Berkeley, CA, United States, v. 21, p. 17–37, 1967. DOI: 10.7146/math.scand.a-10841. Disponível em: https://journals.msp.org/mscand/article/view/2483. Acesso em: 25 jul. 2026.