PEETRE, J. On Estimating the Solutions of Hypoelliptic Differential Equations Near the Plane Boundary. MATHEMATICA SCANDINAVICA, [S. l.], v. 9, p. 337–351, 1961. DOI: 10.7146/math.scand.a-10639. Disponível em: https://www.mscand.dk/article/view/10639. Acesso em: 4 may. 2024.