MULLIKIN, A. L.; SMITH, K. T. Elliptic Differential Problems with High Order Boundary Conditions. MATHEMATICA SCANDINAVICA, [S. l.], v. 12, p. 178–188, 1963. DOI: 10.7146/math.scand.a-10681. Disponível em: https://www.mscand.dk/article/view/10681. Acesso em: 18 apr. 2024.