NG, C. T. Universal parallel composition laws and their representations. Mathematica Scandinavica, Berkeley, CA, United States, v. 40, p. 25–45, 1977. DOI: 10.7146/math.scand.a-11673. Disponível em: https://journals.msp.org/mscand/article/view/1970. Acesso em: 25 jul. 2026.