Abstract
Recall that a pure F-structure is a kind of generalized torus action. The main result asserts that if a compact positively curved manifold Mn admits an invariant pure F-structure such that each orbit has positive dimension, then the fundamental group has a finite cyclic subgroup with index less than wn, a constant depending only on n. As an application, we conclude that for all 0<ÎŽâŠ1, the fundamental group of a ÎŽ-pinched n-manifold either has a cyclic subgroup with index less than wn or has order less than w(n,ÎŽ), a constant depending only on n and ÎŽ. In particular, this substantially improves the main result in[Ro1].
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