2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/164110Not every singular homology class is the push-forward of the fundamental class of some manifold. In the same spirit, one can study the following problem: Which singular homology classes are the push-forward of the fundamental class of a given type of manifolds? In the present article, we show that the fundamental classes of negatively curved manifolds cannot be represented by a non-trivial product of manifolds. This observation sheds some light on the functorial semi-norm on singular homology given by products of compact surfaces.this preprint is superseded by arXiv:0806.4540; 8 pagesAlgebraic Topology57N65; 32Q05text