EKE, B. G. On the Angular Derivative of Regular Functions. Mathematica Scandinavica, Berkeley, CA, United States, v. 21, p. 122–127, 1967. DOI: 10.7146/math.scand.a-10851. Disponível em: https://journals.msp.org/mscand/article/view/2472. Acesso em: 25 jul. 2026.