PARTIS, M. T. Commutative Partially Ordered Recursive Arithmetics. Mathematica Scandinavica, Berkeley, CA, United States, v. 13, p. 199–216, 1963. DOI: 10.7146/math.scand.a-10699. Disponível em: https://journals.msp.org/mscand/article/view/2624. Acesso em: 25 jul. 2026.