ScalingStacks

Proof. [02CN]

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Proof.

Fix any q∈Σq\in\Sigma. Since it is not a fixed point of ψ\psi, we can choose a neighborhood Br​(q)B_{r}(q) such that any path-connected component of the intersection of an orbit of ψ\psi with Br​(q)¯\overline{B_{r}(q)} is compact. Let OqO_{q} be one path-connected component of ψ⁡(q)\psi(q) in Br​(q)B_{r}(q). We claim for s>0s>0 sufficiently small, Σ∩Bs​(q)=Oq∩Bs​(q)\Sigma\cap B_{s}(q)=O_{q}\cap B_{s}(q). If not, then there is a sequence pi∈(Br​(q)∖Oq)∩Σp_{i}\in(B_{r}(q)\setminus O_{q})\cap\Sigma converging to qq. We can choose qiq_{i} on the path-connected component of the orbit of pip_{i} in Br​(q)¯\overline{B_{r}(q)} which has least distance to qq. Then si=d⁡(q,qi)>0s_{i}=d(q,q_{i})>0. For ii sufficiently large we have d⁡(qi,Oq)=sid(q_{i},O_{q})=s_{i}. Now consider the rescaled pointed sequence (Br​(q),si−1​dY,q)(B_{r}(q),s_{i}^{-1}d_{Y},q). As i→∞i\rightarrow\infty, by passing to a subsequence, this converges to ℝ×ℂ2/Γ\mathbb{R}\times\mathbb{C}^{2}/\Gamma. Moreover, OqO_{q} converges to ℝ×{0}\mathbb{R}\times\{0\}, and qiq_{i} converges to q∞q_{\infty} which has distance 11 to ℝ×{0}\mathbb{R}\times\{0\}. But qiq_{i} is singular for all ii, so q∞q_{\infty} is also singular. Contradiction. Then the Proposition follows from the claim and an obvious compactness argument. ∎

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