VUCKOVIC, Vladeta. Partially Ordered Recursive Arithmetics. MATHEMATICA SCANDINAVICA, [S. l.], v. 7, p. 305–320, 1959. DOI: 10.7146/math.scand.a-10576. Disponível em: https://www.mscand.dk/article/view/10576. Acesso em: 5 dec. 2025.