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We apply an equivariant version of Perelman’s Ricci flow with surgery to study
smooth actions by finite groups on closed 3–manifolds. Our main result is that such
actions on elliptic and hyperbolic 3–manifolds are conjugate to isometric actions.
Combining our results with results by Meeks and Scott [Invent. Math. 86 (1986)
287-346], it follows that such actions on geometric 3–manifolds (in the sense of
Thurston) are always geometric, ie there exist invariant locally homogeneous
Riemannian metrics. This answers a question posed by Thurston [Bull. Amer. Math.
Soc. (N.S.) 6 (1982) 357-381].
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