HARPER, J.; SCHOCHET, C. Coalgebra Extensions in Two-Stage Postnikov Systems. MATHEMATICA SCANDINAVICA, [S. l.], v. 29, p. 232–236, 1971. DOI: 10.7146/math.scand.a-11048. Disponível em: https://www.mscand.dk/article/view/11048. Acesso em: 3 may. 2024.