KRISTENSEN, Leif. On the Cohomology of Spaces with Two Non-Vanishing Homotopy Groups. Mathematica Scandinavica, Berkeley, CA, United States, v. 12, p. 83–105, 1963. DOI: 10.7146/math.scand.a-10674. Disponível em: https://journals.msp.org/mscand/article/view/2651. Acesso em: 25 jul. 2026.