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Ricci curvature and volume convergence. (English) Zbl 0879.53030
The author gives a new integral estimate of distances and angles on manifolds with a given lower Ricci curvature bound. He obtains this estimate via a Hessian estimate and states it in three different forms. Using this, he proves (among other things) the following conjectures:
1. The volume is a continuous function on the space of all closed $$n$$-manifolds with Ricci curvature greater or equal to $$-(n-1)$$ equipped with the Gromov-Hausdorff metric (a conjecture of Anderson and Cheeger).
2. An almost nonnegatively Ricci curved $$n$$-manifold with first Betti number equal to $$n$$ is a torus (Gromov’s conjecture).
3. An open $$n$$-manifold with nonnegative Ricci curvature, whose tangent cone at infinity is $$\mathbb{R}^n$$, is itself $$\mathbb{R}^n$$ (a conjecture of Anderson and Cheeger).

##### MSC:
 53C23 Global geometric and topological methods (à la Gromov); differential geometric analysis on metric spaces
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