ScalingStacks

Proof. [04PV]

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Proof.

The morphism 𝒡→𝒳i​j​k\mathscr{Z}\rightarrow\mathscr{X}_{ijk} is the blow-up of the 24 exceptional curves of gi​j​kg_{ijk}. In particular, the exceptional divisor EqE_{q} is the preimage in 𝒡\mathscr{Z} of a curve contained in D~l\tilde{D}_{l}; it follows that vEq​(z~l)=1v_{E_{q}}(\tilde{z}_{l})=1 and vEq​(z~h)=0v_{E_{q}}(\tilde{z}_{h})=0, where z~l,z~h\tilde{z}_{l},\tilde{z}_{h} are local equations for D~l,D~h\tilde{D}_{l},\tilde{D}_{h} on 𝒳i​j​k\mathscr{X}_{ijk}. The Berkovich retraction ρ𝒳i​j​k\rho_{\mathscr{X}_{ijk}} is linear on WqW_{q} and hence depends only on the image of vqv_{q}, which is determined by vEq​(z~l)v_{E_{q}}(\tilde{z}_{l}) and vEq​(z~h)v_{E_{q}}(\tilde{z}_{h}). Thus we conclude that ρ𝒳i​j​k​(vq)=vl\rho_{\mathscr{X}_{ijk}}(v_{q})=v_{l} and we have the result. ∎

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