ScalingStacks

Example 2.4 . [015A]

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Example 2.4.

Set 𝒳=𝔻2{\mathcal{X}}={\mathbb{D}}^{2} and D=E0+E1D=E_{0}+E_{1} the union of the coordinate axes, with coordinates (z0,z1)(z_{0},z_{1}). Then 𝒰=𝒳{\mathcal{U}}={\mathcal{X}} is itself an adapted coordinate chart. In these coordinates, Log𝒰:𝒰∖D→σ𝒰\operatorname{Log}_{{\mathcal{U}}}\colon{\mathcal{U}}\setminus D\to\sigma_{\mathcal{U}} becomes the map (𝔻∗)2→[0,1]({\mathbb{D}}^{*})^{2}\to[0,1] sending (z0,z1)(z_{0},z_{1}) to log⁡|z1|/log⁡|z0​z1|\log|z_{1}|/\log|z_{0}z_{1}|. As a consequence, given t∈ℝ+∗t\in{\mathbb{R}}_{+}^{*} and 0<ε≪10<\varepsilon\ll 1, the closure in 𝒳hyb{\mathcal{X}}^{\mathrm{hyb}} of the closed subset

Fε:={0<|z0|,|z1|≤ε,|z0|t+ε≤|z1|≤|z0|t−ε}⊂𝔻2F_{\varepsilon}:=\{0<|z_{0}|,|z_{1}|\leq\varepsilon,|z_{0}|^{t+\varepsilon}\leq|z_{1}|\leq|z_{0}|^{t-\varepsilon}\}\subset{\mathbb{D}}^{2}

is given by F¯ε=Fε∪Iε{\bar{F}}_{\varepsilon}=F_{\varepsilon}\cup I_{\varepsilon}, where Iε:={t∈[0,1]∣t−ε1+t−ε≤t≤t+ε1+t+ε}I_{\varepsilon}:=\{t\in[0,1]\mid\frac{t-\varepsilon}{1+t-\varepsilon}\leq t\leq\frac{t+\varepsilon}{1+t+\varepsilon}\}. Further, the sets F¯ε{\bar{F}}_{\varepsilon}, for 0<ε≪10<\varepsilon\ll 1 form a basis of closed neighborhoods of the point t1+t∈[0,1]\frac{t}{1+t}\in[0,1] in 𝒳hyb{\mathcal{X}}^{\mathrm{hyb}}. See Figure 1.

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