HOLTZMAN, D. N. Product structures in pyramids of higher order cohomology operations. Mathematica Scandinavica, Berkeley, CA, United States, v. 57, p. 155–170, 1985. DOI: 10.7146/math.scand.a-12109. Disponível em: https://journals.msp.org/mscand/article/view/1560. Acesso em: 25 jul. 2026.