ScalingStacks

Proof of Lemma 2.1 . [024S]

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Proof of Lemma 2.1.

Thanks to Lemma 2.3, we can choose a small ν0>0\nu_{0}>0 so that βi>ν0​γi\beta_{i}>\nu_{0}\gamma_{i} for each ii such that γi>0\gamma_{i}>0. It follows from the description in (2.4) that for any 0<ν⩽ν00<\nu\leqslant\nu_{0}, the set π−1​(Eν)∩Z\pi^{-1}(E_{\nu})\cap Z contains an open neighborhood of the point q∈Dℓ∩π−1​(𝒮c)¯q\in D_{\ell}\cap\overline{\pi^{-1}(\mathcal{S}^{c})}. Repeating this finitely many times on a covering of ∑ℓDℓ∩π−1​(𝒮c)\sum_{\ell}D_{\ell}\cap\pi^{-1}(\mathcal{S}^{c}), and using Lemma 2.2, we find ν0>0\nu_{0}>0 such that for any 0<ν⩽ν00<\nu\leqslant\nu_{0}, the set π−1​(Eν∪𝒮)\pi^{-1}(E_{\nu}\cup\mathcal{S}) contains an open neighborhood of V~+∑ℓDℓ\tilde{V}+\sum_{\ell}D_{\ell}. This immediately implies that Eν∪𝒮E_{\nu}\cup\mathcal{S} contains an open neighborhood of pp, since π\pi is an isomorphism away from V~+∑ℓDℓ\tilde{V}+\sum_{\ell}D_{\ell}. ∎

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