HOLTZMAN, D. N. Product structures in pyramids of higher order cohomology operations. MATHEMATICA SCANDINAVICA, [S. l.], v. 57, p. 155–170, 1985. DOI: 10.7146/math.scand.a-12109. Disponível em: https://www.mscand.dk/article/view/12109. Acesso em: 1 may. 2024.