HOLTZMAN, D. N. Pyramids of higher order cohomology operations in the $p$-torsion-free category. Mathematica Scandinavica, Berkeley, CA, United States, v. 57, p. 127–154, 1985. DOI: 10.7146/math.scand.a-12108. Disponível em: https://journals.msp.org/mscand/article/view/1558. Acesso em: 25 jul. 2026.