2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/163747This paper has been withdrawn, because it is subsumed by the new preprint arXiv:0806.4540 .This paper has been withdrawn, because it is subsumed by the new preprint arXiv:0806.4540Geometric TopologyDifferential Geometry53C23On homology classes not representable by productstext