PARTIS, M. T. Commutative Partially Ordered Recursive Arithmetics. MATHEMATICA SCANDINAVICA, [S. l.], v. 13, p. 199–216, 1963. DOI: 10.7146/math.scand.a-10699. Disponível em: https://www.mscand.dk/article/view/10699. Acesso em: 29 apr. 2024.