2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/76415The relationship between the Chern-Simons invariant and eta-invariant of a 3-manifold is shown to lead to an obstruction to a group being the fundamental group of a closed oriented 3-manifold. The proof uses Sunada's construction of isospectral manifolds as covering spaces over a common base space.AMS-LaTeX, 5 pagesGeometric TopologyDifferential GeometryGroup Theory57N10 (Primary) 57M60text