STETKAER, H. Invariant Pseudo-Differential Operators. MATHEMATICA SCANDINAVICA, [S. l.], v. 28, p. 105–123, 1971. DOI: 10.7146/math.scand.a-11009. Disponível em: https://www.mscand.dk/article/view/11009. Acesso em: 1 may. 2024.