EKE, B. G. On the Angular Derivative of Regular Functions. MATHEMATICA SCANDINAVICA, [S. l.], v. 21, p. 122–127, 1967. DOI: 10.7146/math.scand.a-10851. Disponível em: https://www.mscand.dk/article/view/10851. Acesso em: 6 may. 2024.