2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/75014We give lower bounds, in terms of the Euler characteristic, for the $L^2$-norm of the Weyl curvature of closed Riemannian 4-manifolds. The same bounds were obtained by Gursky, in the case of positive scalar curvature metrics.6 pagesDifferential Geometry53C21text