HOLM, Per. Excision and Cofibrations. Mathematica Scandinavica, Berkeley, CA, United States, v. 19, p. 122–126, 1966. DOI: 10.7146/math.scand.a-10800. Disponível em: https://journals.msp.org/mscand/article/view/2544. Acesso em: 25 jul. 2026.