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Let $(M,g)$ be a Riemannian manifold and assume that for all orthonormal $v,z$ the sectional curvatures is bounded from below i.e. $K(v,z) \geq C$, where $C > 0$. Is it in this case possible for the Ricci curvature to vanish? Or is this condition, on the sectional curvature, very strong? Sorry if the question is too trivial :).

Gunam

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    [Wikipedia](http://en.wikipedia.org/wiki/Ricci_curvature#Properties) says that you also get a lower bound on the Ricci curvature.2012-11-10
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    how exactly? do you know?2012-11-10

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