HÖRMANDER, L. On the Uniqueness of the Cauchy Problem II. MATHEMATICA SCANDINAVICA, [S. l.], v. 7, p. 177–190, 1959. DOI: 10.7146/math.scand.a-10571. Disponível em: https://www.mscand.dk/article/view/10571. Acesso em: 3 jul. 2024.