Abstract
The Ricci flow on a compact four-manifold preserves the condition of pointwise 1/4- pinching of flag curvatures. Any compact Riemannian four-manifold with 1/4-pinched flag curvatures is either isometric to $\Bbb C\Bbb P^{2}$ or diffeomorphic to a space-form.
Citation
Ben Andrews. Huy Nguyen. "Four-manifolds with 1/4-pinched Flag Curvatures." Asian J. Math. 13 (2) 251 - 270, June 2009.
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