PEETRE, J. Remark on Eigenfunction Expansions for Elliptic Operators with Constant Coefficients. Mathematica Scandinavica, Berkeley, CA, United States, v. 15, p. 83–92, 1964. DOI: 10.7146/math.scand.a-10731. Disponível em: https://journals.msp.org/mscand/article/view/2615. Acesso em: 25 jul. 2026.