NG, C. T. Universal parallel composition laws and their representations. MATHEMATICA SCANDINAVICA, [S. l.], v. 40, p. 25–45, 1977. DOI: 10.7146/math.scand.a-11673. Disponível em: https://www.mscand.dk/article/view/11673. Acesso em: 3 may. 2024.