KOLSRUD, T. A uniqueness theorem for higher order elliptic partial differential equations. MATHEMATICA SCANDINAVICA, [S. l.], v. 51, p. 323–332, 1982. DOI: 10.7146/math.scand.a-11984. Disponível em: https://www.mscand.dk/article/view/11984. Acesso em: 5 may. 2024.