HARPER, John; SCHOCHET, Claude. 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://tidsskrift.dk/math/article/view/11048. Acesso em: 14 aug. 2026.