NAKAI, M.; SARIO, L. A Property of Biharmonic Functions with Dirichlet Finite Laplacians. Mathematica Scandinavica, Berkeley, CA, United States, v. 29, p. 307–316, 1971. DOI: 10.7146/math.scand.a-11057. Disponível em: https://journals.msp.org/mscand/article/view/2298. Acesso em: 25 jul. 2026.