2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/152137Among all conformal classes of Riemannian metrics on ${\Bbb CP}_2$, that of the Fubini-Study metric is shown to have the largest Yamabe constant. The proof, which involves perturbations of the Seiberg-Witten equations, also yields new results on the total scalar curvature of almost-Kähler 4-manifolds.LaTeX file, 17 pagesDifferential Geometrytext