POGORZELSKI, H. A. Recursive Arithmetic of Skolem II. Mathematica Scandinavica, Berkeley, CA, United States, v. 11, p. 156–160, 1962. DOI: 10.7146/math.scand.a-10662. Disponível em: https://journals.msp.org/mscand/article/view/2686. Acesso em: 25 jul. 2026.