CABRAL, R. A. H. M. . Strongly elliptic operators and exponentiation of operator Lie algebras. MATHEMATICA SCANDINAVICA, [S. l.], v. 127, n. 2, p. 264–286, 2021. DOI: 10.7146/math.scand.a-126020. Disponível em: https://www.mscand.dk/article/view/126020. Acesso em: 22 sep. 2021.