BARRACK, J. Recursive Functions and Regressive Isols. Mathematica Scandinavica, Berkeley, CA, United States, v. 15, p. 29–42, 1964. DOI: 10.7146/math.scand.a-10724. Disponível em: https://journals.msp.org/mscand/article/view/2622. Acesso em: 25 jul. 2026.