EARLE, Clifford J. Some remarks on the Beltrami equation. MATHEMATICA SCANDINAVICA, [S. l.], v. 36, p. 44–48, 1975. DOI: 10.7146/math.scand.a-11561. Disponível em: https://tidsskrift.dk/math/article/view/11561. Acesso em: 13 aug. 2026.