HÖRMANDER, Lars. On the Uniqueness of the Cauchy Problem II. Mathematica Scandinavica, Berkeley, CA, United States, v. 7, p. 177–190, 1959. DOI: 10.7146/math.scand.a-10571. Disponível em: https://journals.msp.org/mscand/article/view/2775. Acesso em: 8 sep. 2026.