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 so that for each such that . It follows from the description in (2.4) that for any , the set contains an open neighborhood of the point . Repeating this finitely many times on a covering of , and using Lemma 2.2, we find such that for any , the set contains an open neighborhood of . This immediately implies that contains an open neighborhood of , since is an isomorphism away from . ∎