PEETRE, J. Remark on Eigenfunction Expansions for Elliptic Operators with Constant Coefficients. MATHEMATICA SCANDINAVICA, [S. l.], v. 15, p. 83–92, 1964. DOI: 10.7146/math.scand.a-10731. Disponível em: https://www.mscand.dk/article/view/10731. Acesso em: 7 may. 2024.